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["필드선택","검색값"]
["권호","37권5호","☜ 필드선택 - 검색값 입력 후 Enter (첫 글자 대소문자 구분)"]
[]
["시트","권호","제목","토픽","초록","키워드","저자","DOI"]

{"sheet":"2019년","index":1,"n_rows":53,"n_cols":7,"rows_kept":53,"cut":false,"hidden":false,"merged":[]}
["권호","제목","토픽","초록","키워드","저자","DOI"]
["35권1호\npp.1-8","플라스틱 기어의 트라이볼로지적 특성 향상을 위한 DLC 코팅 적용                              \n(Evaluation of Tribological Characteristics of Diamond-Like Carbon (DLC) Coated Plastic Gear)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Demand for plastic gears are increasing in many industries due to their low production cost, light weight, applicability without lubricant, corrosion resistance and high resilience. Despite these benefits, utilizing plastic gears is limited due to their poor material properties. In this work, DLC coating was applied to improve the tribological properties of polyamide66 gear. 0 V, 40 V, and 70 V of negative bias voltages were selected as a deposition parameter in DC magnetron sputtering system. Pin-on-disk experiment was performed in order to investigate the wear characteristics of the gears. The results of the pin-on-disk experiment showed that DLC coated polyamide66 with 40 V of negative bias voltage had the lowest friction coefficient value (0.134) and DLC coated PA66 with 0 V of negative bias voltage showed the best wear resistance (9.83×10-10 mm3/N·mm) among all the specimens. Based on these results, durability tests were conducted for DLC coated polyamide66 gears with 0 V of negative bias voltage. The tests showed that the temperature of the uncoated polyamide66 gear increased to about 37oC while the DLC coated gear saturated at about 25oC. Also, the power transmission efficiency of the DLC coated gear increased by about 6% compared to those without coating. Weight loss of the polyamide66 gears were reduced by about 73%.","plastic gear (플라스틱 기어), friction (마찰), wear (마모), diamond-like carbon (다이아몬드상 카본), coating (코팅), tribology (트라이볼로지), sputtering (스퍼터링)","배수민1,2·마디 카뎀1,2·서국진1,2·김대은1,2†\n1연세대학교 기계공학부, 2연세대학교 무한내마모연구단 1Department of Mechanical Engineering, Yonsei University, 2Center for Nano-Wear, Yonsei University ","https://doi.org/10.9725/kts.2019.35.1.1"]
["35권1호\npp.9-15","전사 방법에 따른 그래핀의 표면 에너지 변화\n(Surface Energy of Graphene Transferred by Wet and Dry Transfer Methods)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Graphene is a fascinating material for fabricating flexible and transparent devices owing to its thickness and mechanical properties. To utilize graphene as a core material for devices, the transfer process of graphene is an inevitable step. The transfer process can be classified into wet and dry methods depending on the surrounding environment. The adhesion between graphene and a target substrate determines the success or failure of the transfer process. As the surface energy of graphene is an important parameter that provides adhesion, it is useful to estimate the surface energy to understand the mechanisms of the transfer process. However, the exact surface energy of graphene is still disputed because the wetting transparency of graphene depends on the polarity of the liquid and target substrate. Previously reported results use graphene transferred by the wet method. However, there are few reports on the surface energy of graphene transferred by the dry method. In this study, the surface energy of graphene transferred by the wet and dry methods is estimated. Wetting transparency occurs for certain combinations of liquids and substrates. For graphene on a polar substrate, the surface energy decreases by 25 and 35% for the wet and dry transfer methods, respectively. However, the surface energy of graphene on dispersive substrates decreases by ~10% regardless of the transfer method. In conclusion, the surface energy of graphene is 36~38 mJ/m2, and differs depending on the transfer method and polarity of the substrate.","contact angles (접촉각), surface energy (표면 에너지), graphene (그래핀), wet transfer (습식 전사), dry transfer (건식 전사)","윤민아1,2·김찬1,2·원세정3·정현준3·김재현1,2·김광섭1,2†\n1과학기술연합대학원대학교 나노메카트로닉스학과, 2한국기계연구원 나노융합기계연구본부, 3파동에너지극한제어연구단","https://doi.org/10.9725/kts.2019.35.1.9"]
["35권1호\npp.16-23","표면막과 표면거칠기가 접촉 저항에 미치는 영향\n(Effect of Surface Film and Surface Roughness on Contact Resistance)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification), Contact Mechanics & Friction","In this study, we aim to analyze the effects of both contact layer properties and surface roughness on contact resistance. The contact has a great influence on performance in terms of electrical conduction and heat transfer. The two biggest factors determining contact resistance are the presence of surface roughness and the surface layer. For this reason we calculated the contact resistance by considering both factors simultaneously. The model of this study to calculate contact resistance is as follows. First, the three representative surface parameters for the GW model are obtained by Nayak's random process. Then, the apparent contact area, real contact area, and contact number of asperities are calculated using the GW model with the surface parameters. The contact resistance of a single surface layer is calculated using Mikic's constriction equation. The total contact resistance is approximated by the parallel connection between the same asperity contact resistances. The results of this study are as follows. The appropriate thickness with reduction effect for contact resistance is determined according to the difference in conductivity between the base layer and surface layer. It was confirmed that the standard deviation of surface roughness has the greatest influence on surface roughness parameters. The results of this study will be useful for selecting the surface material and surface roughness when the design considering the contact resistance is needed.","surface film (표면막), surface roughness (표면거칠기), GW model (GW모델), contact resistance (접촉 저항), constriction resistance (수축 저항)","이현철·이보라·유용훈·조용주†\n부산대학교 기계공학부","https://doi.org/10.9725/kts.2019.35.1.16"]
["35권1호\npp.24-29","고온 환경에서 합금의 마모 및 마찰 특성에 관한 연구\n(A Study on Wear Properties of Alloys in High Temperature Condition)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heatresistant materials.","alloy (합금), friction (마찰), high temperature condition (고온 환경), lubrication (윤활), wear (마모)","최승윤1·Narguess Nemati1·김대은2†\n1연세대학교 대학원 기계공학부, 2연세대학교기계공학과","https://doi.org/10.9725/kts.2019.35.1.24"]
["35권1호\npp.30-36","하중 및 온도에 따른 습식 클러치 마찰재의 트라이볼로지 특성\n(Effect of Normal Force and Temperature on Tribological Properties of Wet Clutch Friction Material)","Wear Phenomena & Mechanisms, Automotive Tribology","The tribological properties of paper-based friction materials are crucial to the performance of a wet clutch system. In this work, the friction and wear characteristics of a paper-based friction material in boundary lubrication state was experimentally investigated using a pin-on-reciprocating tribotester under various normal forces and temperatures. It was found that the wear rate of the friction material increased from 5.8×10-6 mm3/N/cycle to 5.5×10-5 mm3/N/cycle after 1,700 cycles of testing at 80°C as normal force increased from 2 N to 7 N. The friction coefficient was also found to increase from 0.135 to 0.155 with increasing normal force from 2 N to 7 N. The increase in contact pressure with increasing normal force may be responsible for these results. In addition, as temperature increased from 20°C to 80°C, the wear rate of the friction materials increased from 2.0×10-5 mm3/N/cycle to 3.6×10-5 mm3/N/cycle while the friction coefficient decreased from 0.163 to 0.146. This result may be associated with the decrease in the hardness of friction materials with increasing temperature. Furthermore, plastic deformation on the friction materials was mainly observed after the test. The outcome of this work may be useful to gain a better understanding of the tribological properties of friction materials, and therefore can contribute to the development of friction materials with enhanced performance for wet clutch systems.","friction (마찰), friction material (마찰재), wear rate (마모율), wet clutch (습식 클러치)","박혜선·정구현†\n울산대학교 기계공학부","https://doi.org/10.9725/kts.2019.35.1.30"]
["35권1호\npp.37-43","볼 베어링의 무차원 형상변수를 이용한 최적 턱 높이 설계\n(Optimum Shoulder Height Design using Non-dimensional Shape Variables of Ball Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.","ball bearing (볼 베어링), contact analysis (접촉해석), shoulder height (턱 높이), edge effect (모서리 효과)","최동철1·김태완2†\n1(주)디에스시 기술연구소, 2부경대학교 기계공학과","https://doi.org/10.9725/kts.2019.35.1.37"]
["35권1호\npp.44-51","가스 포일 베어링으로 지지되는 연료전지 전기자동차용 공기압축기의 회전체동역학적 성능 측정 및 예측\n(Rotordynamic Performance Measurements and Predictions of a FCEV Air Compressor Supported on Gas Foil Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor–GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor–GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.","gas foil bearing (가스 포일 베어링), mass imbalance response (질량 불균형 응답), rotordynamic (회전체동역학), shim foil (심포일), air compressor (공기압축기)","황성호1·문창국1·김태호1†·이종성2·조경석2·하경구3·이창하3\n1국민대학교 대학원 기계설계학과, 2한온시스템 선행부품개발팀, 3현대자동차 연료전지설계팀","https://doi.org/10.9725/kts.2019.35.1.44"]
["35권1호\npp.52-58","자동차 전장 커넥터 방수 시일의 유한요소해석\n(FEM Analysis of a Waterproof Seal of Automotive Electrical Connectors)","Modeling & Simulation in Tribology","In the case of high-voltage connectors applied to automobiles, waterproofing has become an important issue for the safety of automobiles. In this study, structural analysis is performed on silicone rubber- type waterproof seals used in the voltage connector. For the structural analysis, the tensile properties of the actual rubber seal are evaluated using a miniaturized tensile testing machine. The Mooney-Rivlin material constants of the rubber seal are determined as follows; D1=0, C01=0.241, C10=0.0142. The analysis shows that the contact pressure at the top of the seal where the seal and male connector are in contact is approximately three times higher than that at the bottom of the seal where the seal and female connector are in contact. It is confirmed that the waterproofing performance of the rubber seal depends on the contact pressure of the seal bottom where the seal and female connector are in contact. The contact pressure for waterproofing is found to be 4.7 bar. The strain concentration of the curved part is attributed to excessive initial tension. Therefore, a redesign is recommended for uniform stress or strain distribution in the curved section of the seal in response to the stress relaxation problem due to permanent deformation.","connector seal (커넥터 시일), rubber properties (고무 물성치), waterproof seal (방수 시일), contact pressure (접촉 압력)","한정진1·황원태1·김호경2†\n1서울과학기술대학교 일반대학원 자동차공학과, 2서울과학기술대학교 기계·자동차공학과","https://doi.org/10.9725/kts.2019.35.1.52"]
["35권1호\npp.59-64","자동차 헤드램프내 체결부품사이의 마찰계수 실험장치 개발\n(Development of a Measuring Device for Coefficient of Friction between Connection Parts in Vehicle Head Lamps)","Contact Mechanics & Friction","When slipping occurs between two materials, the coefficients of friction must be considered because these values determine the overall efficiency of the machine or slip characteristics. Therefore, it is important to find the coefficient of friction between two materials. This paper focuses on obtaining the coefficient of friction between an aiming bolt and a retainer located in the headlamps of a vehicle. This bolt supports the headlamp, and if the bolt is loosened by external vibration, the angle of the light will change and block the vision of pedestrians or other drivers. In order to study these situations, the coefficient of friction between aiming bolts and retainers needs to be measured. In addition, the coefficient of friction of materials used in the headlamp should be obtained. To determine these two factors, a new device is designed for two cases: surface-surface contact and surface-line contact. To increase reliability of the results, the device is designed using an air-bearing stage which uses compressed air as lubricant to eliminate the friction of the stage itself. Experiments were carried out by applying various vertical forces, and the results show that the coefficient of friction can be measured consistently. The procedure for designing the device and the results are discussed.","aiming bolt (에이밍 볼트), air bearing stage (공기베어링 스테이지), coefficient of friction (마찰계수), retainer (리테이너), head lamp (헤드램프)","백홍1·문지승1·박상신2†·박종명3\n1영남대학교 대학원 기계공학과, 2영남대학교 기계공학부, 3(주)SL","https://doi.org/10.9725/kts.2019.35.1.59"]
["35권1호\npp.65-70","자동차 헤드램프 내의 에이밍 볼트의 풀림 해석 및 실험\n(Analysis of Self Loosening of Aiming Bolts in Vehicle Head Lamp)","Contact Mechanics & Friction","Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.","aiming bolt(에이밍 볼트), headlamp(헤드램프), resistance torque(저항 토크), self-loosening(풀림)","문지승1·백홍1·박상신2†·박종명3\n1영남대학교 대학원 기계공학과, 2영남대학교 기계공학부, 3(주)SL","https://doi.org/10.9725/kts.2019.35.1.65"]
["35권1호\npp.71-76","콘크리트 믹서 감속기의 진동 평가\n(Vibration Evaluation of Concrete Mixer Reducer)","Condition Monitoring & Maintenance System (System Reliability), Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The differential planetary gear reducer as a main component of the concrete mixer driving mechanism requires a strong torque to mix concrete compounds. As this component is currently dependent on imports, it is necessary to develop it by conducting a study on vibration analysis and the resonance problem. The noise and vibration of a concrete mixer reducer increase owing to the transmission error of planetary gears, and the damage of components occurs owing to the problems in design and production. In this study, the tooth-passing frequency is calculated to evaluate the noise and vibration of a mixer reducer, and a fast Fourier transform (FFT) analysis is conducted through a vibration test using an acceleration sensor. The vibration of the reducer is measured at three points of input and output of the shaft and planetary gear housing with fixed and variable revolutions per minute. The operating conditions of gears and bearings are evaluated by performing the FFT analysis, and the resonance problem is verified. The results show that No. 1 pinion and ring gears revolve disproportionately. The amplitude values appear high, and the wear of tooth faces occur in tooth-passing frequencies and harmonic components of No. 1 and No. 2 pinion-ring gears. Therefore, we conclude that design changes in the reducer and a correction of tooth profiles are required.","mixer reducer (믹서 감속기), FFT analysis (FFT분석), differential planetary gear (차동유성기어), noise and vibration (소음 진동)","조연상1†·배명호2\n1동아대학교 기계공학과, 2창원문성대학교 항공정비학부","https://doi.org/10.9725/kts.2019.35.1.71"]
["35권1호\npp.77-86","모튼이펙트 해석을 위한 동역학-구조-유체-열전달 시간과도응답 연성해석 시차적분법에서 시상수 효과 분석\n(Analysis of Integration Factor Effect in Dynamic-Structure-Fluid-Heat Coupled Time Transient Staggered Integration Scheme for Morton Effect Analysis)","Tribology Applications (Industrial Case Studies)","The present study focuses on the effect of staggered integration factor (SIF) on Morton effect simulation results. The Morton effect is a synchronous rotordynamic instability problem caused by the temperature differential across the journal in fluid film bearings. Convection and conduction of heat in the thin film displaces the hot spot, which is the hottest circumferential position in the thin film, from -20 to 40 degrees ahead of the high spot, where the minimum film clearance is experienced. The temperature differential across the journal causes a bending moment and the corresponding thermal bow in the rotating frame acts like a distributed synchronous excitation in the fixed frame. This thermal bow may cause increased vibrations and continued growth of the synchronous orbit into a limit cycle. The SIF is developed assuming that the response of the rotor-lubricant-bearing dynamic system is much quicker than that of the bearing-journal thermal system, and it is defined as the ratio between the simulation time of the thermal system and the rotor-spinning period. The use of the SIF is unavoidable for efficient computing. The value of the SIF is chosen empirically by the software users as a value between 100 and 400. However, the effect of the SIF on Morton effect simulation results has not been investigated. This research produces simulation results with different values of SIF.","staggered integration scheme(시차적분법), multi-physics system(다중물리 시스템), morton effect(모튼이펙트), tilting pad journal bearing (틸팅패드 저널베어링)","서준호1†·정승화2\n1부산대학교 대학원 기계공학부, 2잉거솔랜드 압축기 연구개발본부","https://doi.org/10.9725/kts.2019.35.1.77"]
["35권2호\npp.87-93","오일리스 부시용 고체윤활제 개발\n(Development of Solid Lubricants for Oil-less Bush)","Lubrication (Lubricants & Additives)","This work aims to develop a dry lubricant for oilless bush, especially a solid lubricant, thereby creating a coating method with improved properties of anti-friction and load-carrying capacity without oil lubrication. In this work, spherical-shaped powders of thermosetting resin such as polyimide (PI) are mixed with a binder matrix obtained by mixing a fluorocarbon compound resin such as Polytetrafluoroethylene (PTFE) or Ethylene tetra fluoro ethylene (ETFE) with itself or with a non-fluorocarbon thermoplastic resin such as Polyether ether ketone (PEEK). And these dry lubricant mixtures are thickly coated (200-300 mm in the thickness) on the inner surface of the bush by using a wet-typed air-spray deposition method. It was found that the load-carrying capacity of the solid lubricant for excavator bush (60 mm in diameter) that operates under a high load condition (at 40 MPa) is greatly improved owing to the spherical-shaped powders of thermosetting resin. In addition, the coefficient of friction at the sliding surface is also reduced less than 0.1. Thick coating also lowers the contact stress at the edge of a bush that results in better tribological performances. The result suggests that the lubrication performance and durability life of the bush can be remarkably improved even without lubrication (oil or grease).","oil-less bush(오일리스 부시), friction(마찰), wear life(내구수명), PTFE(불화탄소수지), solid lubrication(고체윤활)","공호성1†·한흥구1·김진욱2·김경석2·박종식3\n1한국과학기술연구원 책임연구원/연구원, 2㈜대금지오웰 본부장/선임연구원, 3J.S. Chem 대표이사","https://doi.org/10.9725/kts.2019.35.2.87"]
["35권2호\npp.94-98","리블렛 표면에서 유적의 젖음성에 대한 수치 해석\n(Wettability Simulation of Oil Droplet on Riblet Surface)","Bio-Tribology/Biomimetics","The riblet structure like shark skin has been widely studied owing to its drag reduction and antifouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie–Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.","oil droplet (유적), riblet (리블렛), wettability (젖음성), oleophobicty (소유성)","김태완†\n부경대학교 기계공학과 교수","https://doi.org/10.9725/kts.2019.35.2.94"]
["35권2호\npp.99-105","DN 250만 250℃고온 스팀환경에서 운전되는 단열 브러쉬 실 마모효과에 관한 실험적 연구\n(Experimental Study on the Wear Effects of a Brush Seal in DN 2.5million in a 250℃ High - temperature Steam Environment)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This study presents an experimental investigation of the wear and oxidation of the bristles of a brush seal in a super-heated steam environment. We construct a model reflecting normal force and radial interference to predict the amount of wear. To monitor the volume loss of the bristle induced by the swirl phenomenon of the rotor, we measure the clearance between the rotor and the brush seal by using a non-contact 3-D device. We calculate the area by using the area-wise measurement method. Considering the obvious brush seal wear variables, we use two disks with different roughness(Ra = 0.1μm and 100μm) to determine the effect of roughness on wear. Considering an actual steam turbine, we utilize a steam generator and super-heater to generate a working fluid (0.95MPa, 523.15K) that has high kinetic energy. We observe the abrasion of the bristles in the hot steam environment through a scanning electron microscope image. This study also conducted energy dispersive X-ray (EDX) analysis for a qualitative evaluation of local chemistry. The results indicate that the wear and elimination of bristles occur on the disk with high roughness, and the weight increases due to oxidation. Furthermore these results, reveal that the bristle oxidation is accelerated more under super-heated steam conditions than under conditions without steam.","brush seal(브러쉬 실), wear(마모), Bristle(강모), Surface roughness(표면거칠기), super-heated steam(과열증기)","하윤석1·하태웅2†·이용복3†\n1연합기술대학원대학교(UST) 에너지-환경융합학과 학생연구원, 2가천대학교 기계공학과 교수, 3한국과학기술연구원 국가기반기술연구본부 책임연구원","https://doi.org/10.9725/kts.2019.35.2.99"]
["35권2호\npp.106-113","몰드성형용 렌즈를 위한 ta-C coating의 응용\n(Application of ta-C Coating on WC Mold to Molded Glass Lens)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to 1586 cm−1, indicating that the sp3 content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.","FCVA, ta-C, hardness, adhesion, CoF, glass molding process, optical lens","Woo-Young Lee1† and Ju-hyun Cho2\n1Researcher, Advanced Materials and Manufacturing Laboratory, Department of Mechanical Science and Engineering, Nagoya University, Japan, 2Director, Photonics & ICT Convergence Research Division, Korea Photonics Technology Institute (KOPTI), Korea","https://doi.org/10.9725/kts.2019.35.2.106"]
["35권2호\npp.114-122","볼 베어링 및 가스 포일 베어링으로 지지되는 소형 고속 전동기의 진동 특성\n(Vibrational Characteristics of High-Speed Motors with Ball Bearings and Gas Foil Bearings Supports)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This study characterizes the coastdown performances of two small electric motors supported on high- speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100–30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30–15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than 0.03 N·m.","high speed motor(고속 전동기), gas foil bearing(가스 포일 베어링), ball bearing(볼 베어링), coastdown(관성정지), acceleration(가속)","서정화1·김태호2†\n1국민대학교 대학원 기계설계학과 연구조교, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.2.114"]
["35권2호\npp.123-131","볼 베어링 및 가스 포일 베어링으로 지지되는 고속 전동기의 회전체 관성정지 및 가속 성능 연구\n(Rotor Coastdown and Acceleration Performances of High-speed Motors Supported on Ball Bearings and Gas Foil Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.","ball bearing (볼 베어링), contact analysis (접촉해석), shoulder height (턱 높이), edge effect (모서리 효과)","문형욱1·서정화1·김태호2†\n1국민대학교 대학원 기계설계학과 연구조교, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.2.123"]
["35권2호\npp.132-138","염기 처리된 montmorillonite를 이용한 다이머산 메틸에스테르의 합성\n(Synthesis of Dimer Acid Methyl Ester Using Base-treated Montmorillonite)","Lubrication (Lubricants & Additives)","In this study, we demonstrate the effects of the acidic properties of montmorillonite (MMT), which is commonly used as a catalyst, on the conversion and selectivity of the dimer acid methyl ester (DAME) synthesis. We synthesize DAME by the dimerization of conjugated linoleic acid methyl ester (CLAME) and oleic acid methyl ester using MMT KSF. Incidentally, trimer acid methyl ester was formed as a by-product during the DAME synthesis. There is a necessity to adequately adjust the strength and quantity of the acid site to control the selectivity of DAME. Therefore, we vary the pH of the MMT acid by using various metal hydroxides. The purpose of this study is to increase the yield of monocyclic dimer acid methyl ester, which is a substance with adequate physical properties for industrial applications (e.g., lubricant and adhesive, etc.), using a heterogeneous catalyst. We report the dimerization of fatty acid methyl ester by using base treated-KSF, and apply it to conjugated soybean oil methyl ester. Then, we transmute the acid site properties of KSF, such as pH of 5 wt.% slurry KSF and various alkali metals (Li, Na, K, Ca). Characterization of base treated-KSF using a pH meter, x-ray diffraction, inductively coupled plasma-atomic emission spectrometer, Brunauer–Emmett–Teller surface analysis, and temperature-programmed desorption. We conduct an analysis of CLAME and DAME using nuclear magnetic resonance spectroscopy, gas chromatography, and gel permeation chromatography. Through these experiments, we demonstrate the effects of the acidic properties of KSF on the conversion and selectivity of the DAME synthesis, and evaluate its industrial potential by application to waste vegetable oil.","dimer acid methyl ester (다이머산 메틸에스테르), conjugated linoleic acid methyl ester (공액 리놀레산 메틸에스테르), waste vegetable oil (폐 식물유), acid clay (산성 백토), base-treated clay (염기 처리된 백토)","육정숙·신지훈·김영운†\n한국화학연구원 탄소자원화연구소 연구원/책임연구원","https://doi.org/10.9725/kts.2019.35.2.132"]
["35권2호\npp.139-147","상대재 내식성이 철강재료의 미끄럼마모 특성에 미치는 영향\n(Effects of Corrosion Resistance Characteristics of OpponentMaterials in relative Motion on Sliding Wear Behaviorof Mild Carbon Steel)","Tribochemistry","This study investigates the effects of corrosion resistance characteristics of opponent materials in relative motion on the sliding wear behavior of mild carbon steel. Pin specimens made of mild carbon steel are tested at several sliding speeds against mating discs made of two types of alloyed steels, such as type D2 tool steel (STD11) and type 420 stainless steel (STS420J2), with different corrosion resistance characteristics in a pin-on-disc type sliding wear test machine. The results clearly show that the sliding wear behavior of mild carbon steel is influenced by the corrosion resistance characteristics of the mating disc materials at low sliding speeds. However, the sliding wear behavior at high sliding speeds is irrelevant to the characteristics because of the rising temperature. During the steady state wear period, the sliding wear rate of mild carbon steel against the type 420 stainless steel at a sliding speed of 0.5 m/s increases considerably unlike against the type D2 tool steel. This may be because the better corrosion resistance characteristics achieve a worse tribochemical reactivity. However, during the running-in wear period at low sliding speeds, the wear behavior of mild carbon steel is influenced by the microstructure after heat treatment of the mating disc materials rather than by their corrosion resistance characteristics.","corrosion resistance (내식성), opponent material (상대재), mild carbon steel (탄소강), tribochemical reaction (트라이보케미칼 반응), sliding wear behavior (마모거동)","이한영\n계명대학교 신소재공학과 교수","https://doi.org/10.9725/kts.2019.35.2.139"]
["35권3호\npp.151-157","UV-Vis 분광분석에 의한 전기변압기 내 절연지 열화도 측정\n(Application of UV-Vis Spectroscopic Analysis forTransformer Insulating Paper Degradation)","Condition Monitoring & Maintenance System (System Reliability)","Insulated oil degradation produces charged by-products, such as acids and hydro-peroxides, which tend to reduce the insulating properties of the oil. In this study, UV-vis spectroscopy measurement technology is developed and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate its ability to monitor the degradation of electrical insulating paper. The degradation characteristics of the insulating paper are appropriately represented through various types of measurement methods, such as the Tan (delta) method, CO2 gas production measurement, the titration method, and IR spectroscopy. The results are demonstrated to be well comparable to a change in the fluorescence emission ratio (FER), which is defined as the shift in fluorescence intensity in the measured wavelength range, and also to the chromatic ratio, which is defined as a color shift to longer wavelength ranges. The results also show that, by using UV-vis spectroscopy, it is possible to detect the degradation of the insulating paper. This study suggests that UV-vis spectroscopy can be applied as an alternative to high-performance liquid chromatography, which is the internationally recognized measurement technology for cellulose paper degradation. The FER detector is also verified to be useful as an effective condition-monitoring device for power transformers.","electrical insulating oil(전기절연유), insulating paper(절연지), degradation(열화), UV-Vis spectroscopy(자외선-가시광선 광분광분석기), monitoring(모니터링)","공호성1†·한흥구2\n1한국과학기술연구원 트라이볼로지연구팀 책임연구원, 2한국과학기술연구원 트라이볼로지연구팀 연구원","https://doi.org/10.9725/kts.2019.35.3.151"]
["35권3호\npp.158-168","2.2 kW급 유도전동기의 회전자 적층구조를 고려한 회전체 동역학 해석모델 개발 및 베어링 간극의 영향 분석\n(Rotordynamic Model Development with Consideration of Rotor Core Laminations for 2.2 kW-Class Squirrel-Cage Type Induction Motors and Influence Investigation of Bearing Clearance)","Modeling & Simulation in Tribology","This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.","rotordynamics(회전체동역학), induction motors(유도전동기), laminations of rotor cores(회전자 코어 적층), ball bearing clearance(볼 베어링 간극)","박지수1·심규호2†·이성호3\n1서울과학기술대학교 기계시스템디자인공학과 대학원생, 2서울과학기술대학교 기계시스템디자인공학과 부교수, 3한국생산기술연구원 서남지역본부 수석연구원","https://doi.org/10.9725/kts.2019.35.3.158"]
["35권3호\npp.169-175","Colloidal Probe 원자현미경을 이용한 2차전지 전극용 폴리머 바인더의 응착 및 마찰 특성 평가\n(Assessment of Adhesion and Frictional Properties of Polymer Binders for Secondary Cells using Colloidal Probe Atomic Force Microscope)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","In lithium-ion batteries (LIBs), the stress induced by the volume change of an electrode during charge–discharge processes may often cause the mechanical integrity of the electrode to degrade. Polymer binders with enhanced mechanical properties are preferred for improved mechanical integrity and cycling stability of the electrode. In addition, given that sliding and shearing between the polymer binder and components in the electrode may readily occur, frictional and adhesion characteristics of the polymer binder may play a critical role in the mechanical integrity of the electrode. In this study, frictional and adhesion characteristics of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were investigated using a colloidal probe atomic force microscope. Friction loops were obtained under various normal forces ranging from 0 to 159 nN in air and electrolyte and then the interfacial shear strengths of PAN and PVDF in air were calculated to be 1.4 ± 0.5 and 1.3 ± 0.3 MPa, respectively. The results show that in electrolyte, interfacial shear strength of PAN decreased slightly (1.2 ± 0.2 MPa), whereas that of PVDF decreased drastically (0.06 ± 0.01 MPa). Decreases in mechanical properties and adhesion in electrolyte may be responsible for the decrease in interfacial shear strength in electrolyte. The findings from this study may be helpful in developing polymer binders to improve the mechanical integrity of electrodes in LIBs.","adhesion (응착), atomic force microscopy (원자현미경), friction (마찰), electrolyte (전해질), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF)","웬당쾅1·정구현2†\n1울산대학교 기계공학부 학생연구원, 2울산대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.3.169"]
["35권3호\npp.176-182","단결정 실리콘 웨이퍼의 내마모성 및 내식성 향상에 관한 연구\n(Enhancement of Wear and Corrosion Resistances of Monocrystalline Silicon Wafer)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","The primary objective of this study is to treat a monocrystalline silicon (Si) wafer having a thickness of 279 μm by employing the ultrasonic nanocrystal surface modification (UNSM) technology for improving the efficiency and service life of nano-electromechanical systems (NEMSs) and micro-electromechanical systems (MEMSs) by enhancing of wear and corrosion resistances. The wear and corrosion resistances of the Si wafer were systematically investigated before and after UNSM treatment, wherein abrasive, oxidative and spalling wear mechanisms were applied to the as-received and subsequently UNSM-treated Si wafer. Compared to the as-received state, the wear and corrosion resistances of the UNSM-treated Si wafer are found to be enhanced by about 23% and 14%, respectively. The enhancement in wear and corrosion resistances after UNSM treatment may be attributed to grain size refinement (confirmed by Raman spectroscopy) and modified surface integrity. Furthermore, it is observed that the Raman intensity reduced significantly after UNSM treatment, whereas neither the Raman shift nor new phases were found on the surface of the UNSM-treated Si wafer. In addition, the friction coefficient values of the as-received and UNSM-treated Si wafers are found to be about 0.54 and 0.39, respectively. Hence, UNSM technology can be effectively incorporated as an alternative mechanical surface treatment for NEMSs and MEMSs comprising Si wafers.","silicon wafer (실리콘 웨이퍼), friction and wear behavior (마찰마모 거동), corrosion (부식), ultrasonic nanocrystal surface modification technology (초음파나노표면개질기술)","우르마노프 바흐티요르1·노준석1·편영식2·아마노프 아웨즈한3†\n1선문대학교 대학원 기계공학과 석사과정생, 2선문대학교 기계공학과 교수, 3선문대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2019.35.3.176"]
["35권3호\npp.183-189","윤활제 특성에 따른 시트 리클라이너 부품의 마찰 및 마모 특성\n(The Friction and Wear Characteristics of the Seat Recliner Parts Based on Lubricant Characteristics)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The driver seat of an automobile is in direct contact with the driver and provides the driver with a safe and comfortable ride. The seat consists of a frame, a rail, and many recliners. In recent years, strength and operating force measurement testing of the recliner have become vital for designing car seats. However, performance evaluation requires expensive testing equipment, numerous seat products, and considerable time. Therefore, the trend is to reduce experimentation through interpretation. This study examines the lubrication of solid lubricant for automotive seat recliners and confirms the friction and wear performance. In this study, the lubrication behavior of solid lubricants for car seat recliners is investigated to ascertain the friction and wear performance and to provide accurate values for the strength analysis. The friction material consists of a pin and a plate made from steel, which is widely used in recliners. The friction and wear under lubrication conditions are measured by a reciprocating friction wear tester. The friction coefficient is obtained according to the load and speed. Based on the obtained results, it is possible to achieve a reduction in the error of the test value and the analysis by providing the friction coefficient and wear of the lubricant. The results can be applied to the analysis of automobile seat design.","car seats(자동차 시트), recliner(리클라이너), wear(마모), sliding friction(미끄럼 마찰) friction coefficient(마찰 계수)","홍석준1·이광희2·임현우3·김재웅4·이철희5†\n1인하대학교 대학원 건설기계공학과 석사과정생, 2인하대학교 대학원 기계공학과 박사과정생, 3현대트랜시스㈜ 시트구조설계팀 책임연구원, 4현대트랜시스㈜ 시트구조설계팀 연구원, 5인하대학교 대학원 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.3.183"]
["35권3호\npp.190-198","난류 유동을 갖는 가스 포일 저널 베어링의 성능 예측\n(Performance Predictions of Gas Foil Journal Bearingswith Turbulent Flows)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Gas foil bearings (GFBs) enable small- to medium-sized turbomachinery to operate at ultra-high speeds in a compact design by using ambient air or process gas as a lubricant. When using air or process gas, which have lower viscosity than lubricant oil, the turbomachinery has the advantage of reduced power loss from bearing friction drag. However, GFBs may have high Reynolds number, which causes turbulent flows due to process gas with low viscosity and high density. This paper analyzes gas foil journal bearings (GFJBs) with high Reynolds numbers and studies the effects of turbulent flows on the static and dynamic performance of bearings. For comparison purposes, air and R-134a gas lubricants are applied to the GFJBs. For the air lubricant, turbulence is dominant only at rotor speeds higher than 200 krpm. At those speeds, the journal eccentricity decreases, but the film thickness, power loss, and direct stiffness and damping coefficients increase. On the other hand, the R-134a gas lubricant, which that has much higher density than air, causes dominant turbulence at rotor speeds greater than 10 krpm. The turbulent flow model predicts decreased journal eccentricity but increased film thickness and power loss when compared with the lamina flow model predictions. The vertical direct stiffness and damping coefficients are lower at speeds below 100 krpm, but higher beyond that speeds for the turbulent model. The present results indicate that turbulent flow effects should be considered for accurate performance predictions of GFJBs with high Reynolds number.","gas foil bearing(가스 포일 베어링), turbulent flow(난류), laminar flow(층류), stiffness(강성), damping(감쇠)","문진혁1·김태호2†\n1LG전자 L&A연구센터 연구원, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.3.190"]
["35권4호\npp.199-205","구형 및 평면 원자현미경 탐침에 대한 2차원 소재의 마찰 특성\n(Frictional Properties of Two-dimensional Materials against Spherical and Flat AFM Tips)","Micro/Nano-Tribology","Two-dimensional materials such as graphene, h-BN, and MoS2 have attracted increased interest as solid lubricant and protective coating layer for nanoscale devices owing to their superior mechanical properties and low friction characteristics. In this work, the frictional properties of single-layer graphene, h-BN, and MoS2 are experimentally investigated under various normal forces using atomic force microscope (AFM) tips with a spherical and flat end, with the aim to gain a better understanding of frictional behaviors. The nonlinear relationship between friction and normal force friction was clearly observed for single-layer graphene, h-BN, MoS2 specimens slid against the spherical and flat AFM tips. The results also indicate that single-layer graphene, h-BN, MoS2 exhibit low frictional properties (e.g., friction coefficient below 0.1 under 70~100 nN normal force). In particular, graphene is found to be superior to h-BN and MoS2 in terms of frictional properties. However, the friction of single-layer graphene, h-BN, MoS2 against the flat tip is larger than that against the spherical tip, which may be attributed to the relatively large adhesion. Furthermore, it is shown that the fluctuation of friction is more significant for the flat tip than the spherical tip. The resutls of this study may be helpful to elucidate the feasibility of using two-dimensional materials as solid lubricant and protective coating layer for nanoscale devices.","adhesion (점착), atomic force microscopy (원자현미경), friction (마찰), graphene (그래핀), h-BN (육방정계 질화붕소), MoS2 (이황화몰리브덴)","Tran-Khac Bien-Cuong1ㆍ정구현2†\n1울산대학교 기계공학부 연구원, 2울산대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.4.199"]
["35권4호\npp.206-214","차량용 에어컨에 사용되는 냉매 및 냉동기유의 기술 동향\n(Development Trends of Refrigerant and Refrigerant Oil for Automotive Air-conditioner)","Lubrication (Lubricants & Additives) ,Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This study investigates alternative refrigerants and refrigerant oils as well as the tendency of protecting the global environment in view of automobile air-conditioning systems. Since decades, the R12 refrigerant is not used in automobile air-conditioners because of the ozone depletion potential (ODP) problem, and for the last 20 years, the ODP-free R134a refrigerant is leading the new automotive air-conditioning market. However, owing to its high global warming potential (GWP), the R134a refrigerant use in automobile air-conditioning\nsystem is also prohibited by law, and alternative refrigerants with a low GWP need to be proposed. Therefore, recently, the application of R1234yf, R152a, or other alternative refrigerants has started worldwide. By contrast, natural refrigerant R744 was introduced in the market several years ago by VDA (Verband Der Automobilindustrie), which is a German association in the automotive industry. This study also deals with refrigerant oils. For a long time, polyalkylene glycol (PAG) oil has been traditionally used with automobile air-conditioners, and\npolyolester (POE) oil is suitable for HEV, PHEV, and EV air-conditioning systems, where it is used by the electrically driven compressor owing to its excellent electrical insulation properties. Finally, PAG is an excellent lubricant for all the R134a, R152a, R1234yf, and R744 refrigerants, and has the advantage that it can be applied rapidly to alternative refrigerant air-conditioning systems.","air-conditioning system(에어컨 시스템), automobile(자동차), GWP(지구 온난화 지수), DP(오존층파괴 지수), refrigerant(냉매), refrigerant oil(냉동 윤활유)","이대웅ㆍ황승용†\n한온시스템 연구본부 APIC, 책임연구원","https://doi.org/10.9725/kts.2019.35.4.206"]
["35권4호\npp.215-221","이중 제로터의 설계 및 응용 가능성에 대한 연구\n(Design and Feasibility Study of Double Gerotor)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","A gerotor set consists of two elements, an inner rotor and an outer rotor. The outer rotor has one more tooth than the inner rotor and has its centerline positioned at a fixed eccentricity from the centerline of the inner rotor. Although gerotors come in a variety of geometric configurations, all gerotor sets share the basic principle of having generated tooth profiles that provide continuous tight sealing during operation. The size of the gerotor is proportional to the number of teeth and the amount of eccentricity. The interior of an inner rotor with a large number of teeth has an enough space to include other machine elements. In this paper, the double gerotor mechanism, constructed by putting a small gerotor in the interior of a large inner rotor, is conceptualized. The double gerotor set is composed of an inner rotor, a planetary rotor, and an outer rotor. The inside profile of the planetary rotor corresponds to the outer rotor profile of the small gerotor, and the outside profile is the inner rotor profile of the large gerotor. In the double gerotor, the centers of the inner and the outer rotor are coincident because the eccentricities of two gerotors are balanced. The operation of a double gerotor is examined by analyzing the planetary motion, and a feasibility study for application of the double gerotor for hydraulic motors and pumps is performed.\nThe double gerotor set has much application potential as a component of hydraulic systems.","double gerotor(이중제로터), hydraulic motor(유압모터), hydraulic pump(유압펌프), planetary rotor(유성로터)","이성철†\n인하공업전문대학 기계과 교수","https://doi.org/10.9725/kts.2019.35.4.215"]
["35권4호\npp.222-228","가속노화조건 하 연료접촉 고무오링의 수명예측 및 누유시험 연구\n(A Study on the Lifetime Estimation and Leakage Test of Rubber O-ring in Contacted with Fuel at Accelerated Thermal Aging Conditions)","Others","As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.","liquid fuel (액체연료), rubber O-ring (고무 오링), compression set (압축영구줄음율), lifetime prediction (수명 예측), leakage test(누유시험)","정근우1†ㆍ홍진숙2ㆍ김영운1ㆍ한정식3ㆍ정병훈3ㆍ권영일4\n1한국화학연구원 환경자원연구센터 책임연구원, 2한국화학연구원 환경자원연구센터 연구원, 3국방과학연구소 책임연구원, 4청주대학교 산업공학과 교수","https://doi.org/10.9725/kts.2019.35.4.222"]
["35권4호\npp.229-236","세 물체 간 마찰 완전 접촉 문제의 응력 특이성 거동\n(Stress Singularity Behaviour in the Frictional Complete Contact Problem of Three Bodies)","Contact Mechanics & Friction","This study investigates the stress singularity that occurs at the contact edge of three bodies in a frictional complete contact. We use the asymptotic analysis method, wherein we constitute an eigenvalue problem and observe the eigenvalue behavior, which we use to obtain the order of the stress singularity. For the present geometry of three bodies in contact, a contact between a cracked indenter and half plane is considered. This is a typical geometry of the PCMI problem of a nuclear fuel rod. Thus, this paper, specifically presents the characteristics of the PCMI problem from the perspective of stress singularity. Consequently, it is noted that the behavior of the stress singularity varies with the difference in the crack angle, coefficient of friction, and material dissimilarity, as is observed in a frictional complete contact of two bodies. In addition, we find that the stress singularity changes essentially linearly with respect to the coefficient of friction, regardless of the variation in the crack angle and material dissimilarity. Concurrently, we find the order of singularity to be 0.5 at a certain coefficient of friction, irrespective of the crack angle, which we also observe in the crack problem of a homogeneous and isotropic body. The order of singularity can also exceed 0.5 in the frictional complete contact problem of three bodies. This implies that the propensity for failure when three bodies are in frictional complete contact can be even worse than that in case of a failure induced by a crack.","frictional complete contact of three bodies(세 물체 마찰 완전접촉), asymptotic analysis(점근 해석), eigenvalue problem(고유치 문제), order of stress singularity(응력 특이성 지수)","김형규1†\n1한국원자력연구원 ATF기술개발부 책임연구원","https://doi.org/10.9725/kts.2019.35.4.229"]
["35권4호\npp.237-243","니들 롤러 베어링의 피로 수명 향상에 대한 연구\n(Improvement in Fatigue Life of Needle Roller Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to 0.149 μm and an increase in surface hardness from 58 to 62 HRc.","needle roller bearing(니들 롤러 베어링), surface roughness(표면 거칠기), surface hardness(표면 경도), rolling contact fatigue(RCF, 구름 접촉 피로), ultrasonic nanocrystal surface modification(UNSM)(초음파나노표면개질)","다리스렝 스르멩닥와1ㆍ아마노프 아웨즈한2ㆍ편영식3†\n1선문대학교 기계공학과 박사과정, 2선문대학교 기계공학과 조교수, 3선문대학교 기계공학과 교수","https://doi.org/10.9725/kts.2019.35.4.237"]
["35권4호\npp.244-266","파이어링 시동 사이클 초기에서의 엔진 베어링 마모 시뮬레이션\n(Wear Simulation of Engine Bearings in the Beginning)","Automotive Tribology","The purpose of this study is to estimate the wear volumes of engine journal bearings operating at variable angular velocity of a shaft in the beginning of firing start-up cycle. To do this, first we find the potential region of wear scar on engine journal bearings where the applied bearing load and crank shaft velocity are variable. The potential wear regions are discovered by finding minimum oil film thickness at every crank angle existing below most oil film thickness scaring wear (MOFTSW) obtained based on the concept of the centerline\naverage surface roughness. Then we calculate the wear volume from the wear depth and two wear angles decided by the magnitude of each film thickness lower than MOFTSW at every crank angle. The results show that the expected wear region is located at a few bearing angles after and/or behind the upper center of a big-end bearing and the lower center of a main bearing. And the real wear region is similar to the estimated wear region. Further we find that the wear scar on an engine journal bearing may occur at re-starting time after switch-off of a start motor especially under the condition of high oil temperature.","firing start-up cycle(파이어링 시동 사이클), variable angular velocity and dynamic loads(변동 각 속도 및 동적 하중), most oil film thickness scaring wear(마모유발최대유막두께), asperity contact(돌기접촉),\nwear volume(마모체적)","전상명†\n호서대학교 기계공학부 자동차공학전공 교수","https://doi.org/10.9725/kts.2019.35.4.244"]
["35권5호\npp.267-273","초탄성 및 점탄성 물성을 고려한 자동차용 휠 베어링 실의 드래그 토크 예측\n(Drag Torque Prediction for Automotive Wheel Bearing Seals Considering Viscoelastic as Well as Hyperelastic Material Properties)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Wheel bearings are important automotive parts that bear the vehicle weight and translate rotation motion; in addition, their seals are components that prevent grease leakage and foreign material from entering from the outside of the bearings. Recently, as the need for electric vehicles and eco-friendly vehicles has been emerging, the reduction in fuel consumption and CO2 emissions are becoming the most important issues for automobile manufacturers. In the case of wheel bearings, seals are a key part of drag torque. In this study, we investigate the prediction of the drag torque taking into consideration the hyperelastic and viscoelastic material properties of automotive wheel bearing seals. Numerical analysis based on the finite element method is conducted for the deformation analyses of the seals. To\nimprove the reliability of the rubber seal analysis, three types of rubber material properties are considered, and analysis is conducted using the hyperelastic material properties. Viscoelastic material property tests are also conducted. Deformation analysis considering the hyperelastic and viscoelastic material properties is performed, and the effects of the viscoelastic material properties are compared with the results obtained by the consideration of the hyperelastic material properties. As a result of these analyses, the drag torque is 0.29 Nm when the hyperelastic characteristics are taken into account, and the drag torque is 0.27 Nm when both the hyperelastic and viscoelastic characteristics are taken into account. Therefore, it is determined that the analysis considering both hyperelastic and viscoelastic characteristics must be performed because of its reliability in predicting the drag torque of the rubber seals.","automotive wheel bearing(자동차용 휠 베어링), rubber seal(고무 실), hyperelastic analysis(초탄성 해석), viscoelastic analysis(점탄성 해석), drag torque(드래그 토크)","이승표†\n㈜일진글로벌 기술연구소 이사","https://doi.org/10.9725/kts.2019.35.5.267"]
["35권5호\npp.274-285","화학기계적 연마기술 연구개발 동향: 입자 거동과 기판소재를 중심으로\n(Chemical Mechanical Polishing: A Selective Review of R&D Trends in Abrasive Particle Behaviors and Wafer Materials)","Chemical Mechanical Polishing","Chemical mechanical polishing (CMP), which is a material removal process involving chemical surface reactions and mechanical abrasive action, is an essential manufacturing process for obtaining high-quality semiconductor surfaces with ultrahigh precision features. Recent rapid growth in the industries of digital devices and semiconductors has accelerated the demands for processing of various substrate and film materials. In addition, to solve many issues and challenges related to high integration such as micro-defects, non-uniformity, and\npost-process cleaning, it has become increasingly necessary to approach and understand the processing mechanisms for various substrate materials and abrasive particle behaviors from a tribological point of view. Based on these backgrounds, we review recent CMP R&D trends in this study. We examine experimental and analytical studies with a focus on substrate materials and abrasive particles. For the reduction of micro-scratch generation, understanding the correlation between friction and the generation mechanism by abrasive particle behaviors is critical. Furthermore, the contact stiffness at the wafer-particle (slurry)-pad interface should be carefully considered. Regarding substrate materials, recent research trends and technologies have been introduced that focus on sapphire (α-alumina, Al2O3), silicon carbide (SiC), and gallium nitride (GaN), which are used for organic light emitting devices. High-speed processing technology that does not generate surface defects should be developed for low-cost production of various substrates. For this purpose, effective methods for reducing and removing surface residues and deformed layers should be explored through tribological approaches. Finally, we present future challenges and issues related to the CMP process from a tribological perspective.","chemical mechanical polishing(화학기계적 연마), abrasive wear(연삭 마멸), contact Stiffness(접촉 강성), sapphire(사파이어), silicon carbide(탄화규소), gallium nitride(질화갈륨)","이현섭1ㆍ성인하2†\n1동명대학교 기계공학부 조교수, 2한남대학교 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.5.274"]
["35권5호\npp.286-293","마찰력현미경을 이용한 나노스케일 마멸시험 시 다이아몬드 탐침으로의 MoS2 마멸입자 전이현상\n(Material Transfer of MoS2 Wear Debris to Diamond Probe Tip in Nanoscale Wear test using Friction Force Microscopy)","Micro/Nano-Tribology","In friction and wear tests that use friction force microscopy (FFM), the wear debris transfer to the tip apex that changes tip radius is a crucial issue that influences the friction and wear performances of films and coatings with nanoscale thicknesses. In this study, FFM tests are performed for bilayer MoS2 film to obtain a better understanding of how geometrical and chemical changes of tip apex influence the friction and wear properties of nanoscale molecular layers. The critical load can be estimated from the test results based on the clear distinction of the failure area. Scanning electron microscopy and energy-dispersive spectroscopy are employed to measure and observe the geometrical and chemical changes of the tip apex. Under normal loads lower than 1000 nN, the reuse of tips enhances the friction and wear performance at the tip-sample interface as the contact pair changes with the increase of tip radius. Therefore, the reduction of contact pressure due to the increase of tip radius by the transfer of MoS2 or Mo-dominant wear debris and the change of contact pairs from diamond/MoS2 to partial MoS2 or Mo/MoS2 can explain the critical load increase that results from tip reuse. We suggest that the\nwear debris transfer to the tip apex should be considered when used tips are repeatedly employed to identify the tribological properties of ultra-thin films using FFM.","friction force microscopy(마찰력 현미경), diamond probe tip(다이아몬드 탐침), wear debris transfer(마멸입자 전이), friction and wear test(마찰마멸 시험), bilayer MoS2(이황화몰리브덴 2층 분자막)","송현준1ㆍ임형우1ㆍ성권일1,2ㆍ안효석3†\n1서울과학기술대학교 기술경영융합대학 MSDE전공 학부생, 2MH POWER SYSTEMS KOREA 엔지니어, 3서울과학기술대학교 기술경영융합대학 MSDE전공 교수","https://doi.org/10.9725/kts.2019.35.5.286"]
["35권5호\npp.294-299","Laser Groove 표면의 젖음 특성에 관한 연구\n(Wettability Characteristics of the Laser Grooved Surfaces)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Most previous studies on water repellent surfaces using lasers rely on the use of pico- or femtosecond lasers. However, in industrial application, these methods have the disadvantages of high cost and low efficiency. In this study, we implement a hydrophobic surface using a high-power general-purpose diode laser. We have fabricated the microsurface using laser groove processing technology, and we present the correlation of wettability characteristics with space and width. The metal material is stainless steel (SUS 304), and the groove height during laser processing is set to 30 μm to evaluate the wettability based on the gap and width of various grooves. Results show that the contact angle of the groove-shaped surface is increased by 40° or more as compared with the surface without patterning, and\nthe contact angle in the parallel direction is greater than that in the perpendicular direction. Results from contact angle hysteresis measurement experiments show that the groove width has a greater influence on the contact angle history than does the gap between grooves. In addition, the coating reveals that the contact angle can be increased using a chemical method and that the laser grooving process can further improve the wetting properties of the surface.","contact angle(접촉각), laser groove(레이저 그루브), wettability(젖음성)","장무연1ㆍ김태완2†\n1부경대학교 대학원 기계공학과 석사과정생, 2부경대학교 기계공학과 교수","https://doi.org/10.9725/kts.2019.35.5.294"]
["35권5호\npp.300-309","난류 유동을 갖는 가스 포일 스러스트 베어링의 성능 예측\n(Performance Predictions of Gas Foil Thrust Bearings with Turbulent Flow)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Gas foil thrust bearings (GFTBs) support axial loads in oil-free, high speed rotating machinery using air or gas as a lubricant. Due to the inherent low viscosity of the lubricant, GFTBs often have super-laminar flows in the film region at operating conditions with high Reynolds numbers. This paper develops a mathematical model of a GFTB with turbulent flows and validates the model predictions against those from the literature. The pressure distribution, film thickness distribution, load carrying capacity, and power loss are predicted for both\nlaminar and turbulent flow models and compared with each other. Predictions for an air lubricant show that the GFTB has high Reynolds numbers at the leading edge where the film thickness is large and relatively low Reynolds numbers at the trailing edge. The predicted load capacity and power loss for the turbulent flow model show little difference from those for the laminar flow model even at the highest speed of 100 krpm, because the Reynolds numbers are smaller than the critical Reynolds number. On the other hand, refrigerant (R-134a) lubricant, which has a higher density than air, had significant differences due to high Reynolds numbers in the film region, in particular, near the leading and outer edges. The predicted load capacity and power loss for the turbulent flow model are 2.1 and 2.3 times larger, respectively, than those for the laminar flow model, thus implying that the turbulent flow greatly affects the performance of the GFTB.","gas foil thrust bearing(가스 포일 스러스트 베어링), turbulent flow(난류), laminar flow(층류), load carrying capacity(하중지지능력)","문진혁1ㆍ김태호2†\n1LG전자 HAE연구센터 연구원, 2국민대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2019.35.5.300"]
["35권5호\npp.310-316","고속 공기 스핀들 설계를 위한 근사해석과 회전체동역학의 비교\n(Comparison of Approximation and Rotordynamics Solutions for Design of a High Speed Air Spindle)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This paper presents two methods for designing a high-speed air spindle operated over the rotational speed of 50,000 rpm. The first method is an approximate method, which assumes a symmetric spindle shape even though it is not symmetric in reality. The second is an analysis of rotordynamics using beam and solid models. The approximate method can be used to calculate the bearing load capacities, stiffness and damping coefficients, stability of the shaft system, and response of the forced excitation from the unbalanced mass. Designers can use this method to determine the dimensions of the desired spindle at the first stage of the design. The more detailed\nbehavior of the spindle can be calculated using the rotordynamics theory using beam and solid models based on the Finite Element Method. In this paper, a spindle, with two air bearings, one motor at the end, and two air thrust bearings, is newly developed. The solutions from the two rotordynamics theories are compared with the solution obtained using the approximate method. The three calculations are in agreement, and the procedure for the design of a spindle system, supported on the externally pressurized air bearings, ispresented and discussed.","high speed spindle(고속 스핀들), approximate method(근사 해법), exact solution(적확해), beam and solid modeling(보와 고체 모델), stiffness and damping(강성 및 감쇠)","이재혁1ㆍ박상신2†\n1영남대학교 대학원 기계공학과 석사과정생, 2영남대학교 기계공학부 교수","https://doi.org/10.9725/kts.2019.35.5.310"]
["35권5호\npp.317-322","마모 입자가 음향방출신호에 미치는 영향에 관한 연구\n(Investigation of the Effect of Wear Particles on the Acoustic Emission Signal)","Condition Monitoring & Maintenance System (System Reliability)","In spite of progress in tribological research, machine component failure due to friction and wear has been reported frequently. This failure may lead to secondary damage that can cause huge expense for maintenance and repair. To prevent economic loss, it is important to detect and predict the initial failure point. In this sense, various researchers have been tried to develop Condition Monitoring (CM) method using Acoustic Emission (AE) generated while the materials undergo failure. In this study, effect of particles on friction and wear was investigated using the pin-on-plate friction test and AE signal was recorded with a band-width type AE sensor. The experiments were performed in dry and lubricant conditions using steel and glass as specimens. After the experiment, 3D laser microscope image was captured to evaluate the wear behavior quantitatively. The AE signal was analyzed in time-domain and frequency-domain. The amplitude was compared with the frictional results. The results of this study showed that particle generation accelerate wear, generate high magnitude AE signal and change the frequency characteristics of the signal. Also, lubricant condition test results showed low coefficient\nof friction, low wear rate, and low magnitude of AE signal compared to the dry condition. It is expected that the results of this study will aid in better assessment of wear in CM technology.","acoustic emission(음향 방출), wear(마모), friction(마찰), particle(입자), condition monitoring(상태 진단)","한재호1ㆍ신동갑2ㆍ김대은3†\n1연세대학교 대학원 기계공학과 석사과정생, 2연세대학교 대학원 기계공학과 박사과정생, 3연세대학교 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.5.317"]
["35권6호\npp.323-329","랩그라인딩 후 사파이어 웨이퍼의 표면거칠기가 화학기계적 연마에 미치는 영향\n(Effect of Surface Roughness of Sapphire Wafer on Chemical Mechanical Polishing after Lap-Grinding)","Chemical Mechanical Polishing ","Sapphire is currently used as a substrate material for blue light-emitting diodes (LEDs). The market for sapphire substrates has expanded rapidly as the use of LEDs has extended into various industries. However, sapphire is classified as one of the most difficult materials to machine due to its hardness and brittleness. Recently, a lap-grinding process has been developed to combine the lapping and diamond mechanical polishing (DMP) steps in a single process. This paper studies, the effect of wafer surface roughness on the chemical mechanical polishing (CMP) process by pressure and abrasive concentration in the lap-grinding process of a sapphire wafer. In this experiment, the surface roughness of a sapphire wafer is measured after lap-grinding by varying the pressure and abrasive concentration of the slurry. CMP is carried out under pressure conditions of 4.27 psi, a plate rotation speed of 103 rpm, head rotation speed of 97 rpm, and slurry flow rate of 170 ml/min. The abrasive concentration of the CMP slurry was 20wt, implying that the higher the surface roughness after lap-grinding, the higher the material removal rate (MRR) in the CMP. This is likely due to the real contact area and actual contact pressure between the rough wafer and polishing pad during the CMP. In addition, wafers with low surface roughness after lap-grinding show lower surface roughness values in CMP processes than wafers with high surface roughness values; therefore, further research is needed to obtain sufficient surface roughness before performing CMP processes.","sapphire wafer(사파이어 웨이퍼), lap-grinding(랩그라인딩), chemical mechanical polishing(화학기계적연마), surface roughness(표면거칠기)","서준영1ㆍ이현섭2†\n1동명대학교 대학원 기계시스템공학과 석사과정생, 2동명대학교 기계공학부 조교수","https://doi.org/10.9725/kts.2019.35.6.323"]
["35권6호\npp.330-336","CMP 컨디셔너의 다이아몬드 입자 모양이 연마 패드 표면 형상 제어에 미치는 영향\n(Effect of Diamond Abrasive Shape of CMP Conditioneron Polishing Pad Surface Control)","Chemical Mechanical Polishing","Conditioning is a process involving pad surface scraping by a moving metallic disk that is electrodeposited with diamond abrasives. It is an indispensable process in chemical-mechanical planarization, which regulates the pad roughness by removing the surface residues. Additionally, conditioning maintains the material removal rates and increases the pad lifetime. As the conditioning continues, the pad profile becomes unevenly to be deformed, which causes poor polishing quality. Simulation calculates the density at which the diamond abrasives on the conditioner scratch the unit area on the pad. It can predict the profile deformation through the control of conditioner dwell time. Previously, this effect of the diamond shape on conditioning has been investigated with regard to microscopic areas, such as surface roughness, rather than global pad-profile deformation. In this study, the effect of diamond shape on the pad profile is evaluated by comparing the simulated and experimental conditioning using two conditioners: a) random-shaped abrasive conditioner (RSC) and b) uniform-shaped abrasive conditioner (USC). Consequently, it is confirmed that the USC is incapable of controlling the pad profile, which is consistent with the simulation results.","abrasive wear(연삭 마모), chemical mechanical planarization(화학 기계적 평탄화), conditioning simulation(컨디셔닝 시뮬레이션), pad conditioning(패드 컨디셔닝), pad profile(패드 프로파일)","이동환1ㆍ이기훈1ㆍ정선호1ㆍ김형재2ㆍ조한철3†ㆍ정해도4†\n1부산대학교 대학원 기계공학부 대학원생, 2한국생산기술연구원 동남권본부 정밀가공제어그룹 책임연구원, 3한국생산기술연구원 동남권본부 정밀가공제어그룹 선임연구원, 4부산대학교 대학원 기계공학부 교수","https://doi.org/10.9725/kts.2019.35.6.330"]
["35권6호\npp.337-342","3D 프린팅된 표면의 슬라이딩 방향에 따른 트라이볼로지적 특성 연구\n(A Study on Tribological Properties of 3D-Printed Surfacewith Respect to Sliding Orientation)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","This paper presents an experimental investigation of friction and wear characteristic with respect to patterns occurring on the surface of 3D printed polymer products by fused deposition modeling method. The purpose of this study was to investigate the effect of the patterns and sliding directions on the tribological properties of 3D printed polymer surface. A cubic specimen was printed using polylactic acid filament as the printing material. Friction tests were conducted for different directions with respect to the patterns that were generated on the top and the side surfaces of the specimen, by using a ball-on-reciprocating type tribotester. SUJ2 bearing ball of which the diameter was 11 times greater than the width of the largest pattern was used as the counter surface to assess the frictional behavior. Friction tests were conducted on the top and the side surfaces with respect to the patterns in 3 (0o, 45o, 90o) different directions respectively. Coefficient of friction increased as cycles increased in all cases. The results of the tests showed that the lowest coefficient of friction was measured with the 45o sliding direction on the side surface. The wear rate was the lowest at 45o sliding direction on the side surface, while it was the highest at 0o sliding direction on the top surface. Coefficient of friction of about 0.45 was determined to be the converging value on the top compared to the side surface.","3D printing(3D 인쇄), fused deposition modeling(융합적층모델링), pattern(패턴), polymer(폴리머), tribology(트라이볼로지)","심재웅1ㆍ크리스찬 니콜라스 디카로2ㆍ서국진3ㆍ김대은4†\n1연세대학교 기계공학과 석사과정생, 2캘리포니아대학교 로스엔젤레스 물리천문학과 학부생, 3연세대학교 기계공학과 박사과정생, 4연세대학교 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.6.337"]
["35권6호\npp.343-349","초순수 용매 내 육방정 질화붕소 나노시트의 농도와크기의 관계\n(Relation between the Concentration of Hexagonal Boron Nitride Nano-Sheets Dispersed in Pure Water and Their Width and Height)","Lubrication (Lubricants & Additives)","According to a report in 2011, hexagonal boron nitride demonstrated good solubility in pure water, even without surfactants or organic functionalization. Hexagonal boron nitride nanosheets are an effective lubricant additive, and their solubility in pure water has motivated lubrication engineers to utilize aqueous solutions containing these nanosheets as water-based lubricants. In this study, we measure the width and height of the hexagonal boron nitride nanosheets dispersed in pure water by using the Zetasizer and atomic force microscopy. Without surfactants or functionalization, aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of hexagonal boron nitride nanosheets are synthesized via sonication-assisted hydrolysis. The Zetasizer provides only a one-dimensional size of approximately 410 nm, regardless of the concentration of the solution. Thus, it does not allow the estimation of the shape of the nanosheet. To acquire the three-dimensional size of the nanosheets, atomic force microscopy is employed. The aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of the hexagonal boron nitride nanosheets show average values of 740, 450, 700, and 610 nm in width, and 37, 26, 33, and 32 nm in thickness, respectively. No significant trend is observed between the concentration of the solution and size of the nanosheets. Therefore, when preparing a water-based lubricant, it may be appropriate to adjust conditions such as ultrasonication time rather than the concentration.","dispersion(분산), hexagonal boron nitride(육방정 질화붕소), nano-sheet(나노시트)","조대현1†ㆍ박미영2ㆍ하성훈2\n1경남과학기술대학교 메카트로닉스공학과 조교수, 2경남과학기술대학교 메카트로닉스공학과 학사과정생","https://doi.org/10.9725/kts.2019.35.6.343"]
["35권6호\npp.350-355","Control of Surface Energy using Bilayer Metallic Film Heterostructures","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Surface energy is an important factor in determining the performance of application components in terms of preventing adhesion failure between thin films. In this regard, numerous attempts have been made to acquire the desired surface energy through chemical treatment or by using micro/nanostructures. However, such approaches are expected to provide extreme values of surface energy, which may not be suitable in achieving the enhanced performance of applications. In this study, we propose a method to control surface energy by using bilayer metallic film heterostructures. We measure the water contact angle of incompatible (Ni/Ag) and compatible (Zn/Ag) metal pairs under several experimental factors, including thickness, time, and temperature. Furthermore, we conduct Auger electron spectroscopy measurements to investigate the atomic concentration with respect to depth after the change in the water contact angle. The experimental results reveal that three parameters, namely, compatibility, film thickness, and environmental temperature, are major factors in controlling the water contact angle. Thus, we experimentally demonstrate that controlling these three parameters can provide the approximate desired water contact angle. This result is expected to aid in the performance enhancement of a wide range of application components, where control of surface energy is required.","bi-layer, compatibility, metallic film, surface energy, water contact ang","Chang-Lae Kim1, Dae-Eun Kim2 and Hae-Jin Kim3†\n1Assistant Professor, Dept. of Mechanical Engineering, Chosun University, 2Professor, Dept. of Mechanical Engineering, Yonsei University, 3Assistant Professor, Dept. of Mechanical and Aerospace Engineering, Gyeongsang National University","https://doi.org/10.9725/kts.2019.35.6.350"]
["35권6호\npp.356-361","경계윤활에서 기계 부품 소재의 트라이볼로지적 특성에관한 연구\n(Study on Tribological Characteristics of Machine Componentin Boundary Lubrication)","Tribology Applications (Industrial Case Studies)","The friction and wear between machine components directly influence the energy loss and failure in various machines. Therefore, there is always a demand for finding methods to reduce friction and wear. Of the possible methods, lubrication is a widely used method for reducing friction and wear. In the case of lubrication, it is important to analyze the tribological behavior in the boundary lubrication because most of friction and wear occurs in the boundary lubrication regime. Cast iron has been regarded as a good material for industrial applications due to the excellent mechanical properties and high productivity. Especially, nodular cast iron is a material that shows better mechanical properties and wear-resistance compared with cast iron due to inclusion of spheroidal graphite. In this work, we investigated the tribological characteristics of nodular cast iron with respect to different counter parts in boundary lubrication regime. Sliding tests were conducted with SUJ2, ZrO2, Si3N4balls as counter parts using a pin-on-disk type tribotester. The results showed different friction and wear behaviors with different counter parts. The case of ZrO2 showed the lowest wear rate in specimen and no significant ball wear. In case of SUJ2, it showed similar wear rate with ZrO2 case in specimen and the highest friction coefficient. The case of Si3N4 showed the lowest friction coefficient, 33% lower than the case of SUJ2. It showed 16.9 times larger wear rate in specimen and 43% larger wear rate in ball compared to that of the SUJ2 case.","nodular cast iron(구상흑연주철), sliding friction(미끄럼 마찰), boundary lubrication(경계윤활), friction coefficient(마찰계수), Wear rate(마모율)","김명구1ㆍ서국진2ㆍ남자현3ㆍ김대은4†\n1연세대학교 기계공학과 석사과정생, 2연세대학교 기계공학과 박사과정생, 3삼성전자 생활가전사업부 책임연구원, 4연세대학교 기계공학과 정교수","https://doi.org/10.9725/kts.2019.35.6.356"]
["35권6호\npp.362-368","공정 온도에 따른 사면체 비정질 카본 (ta-C) 코팅의트라이볼로지적 특성연구\n(Effects of Process Temperature on the Tribological Propertiesof Tetrahedral Amorphous Carbon (ta-C) Coating)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","In this study, mechanical and tribological properties were investigated by varying the process temperature (50, 100, 125 and 150 oC) to reduce internal stress. The internal stress reduction by thermal dissociation ta-C coating film with increasing temperature is confirmed through the curvature radius of the ta-C coating according to the temperature of the SUS plate. As the coating temperature increased, the mechanical properties (hardness, modulus, toughness) deteriorated, which is in agreement with the Raman analysis results. As the temperature increased, the sp2 phase ratio increased owing to the dissociation of the sp3 phase. The friction and wear properties are related to the process temperature during ta-C coating. Low friction and wear properties are observed in high hardness samples manufactured at 50 oC, and wear resistance properties decreased with increasing temperature. The contact area is expected to increase owing to the decrease of hardness(72 GPa to 39 GPa) and fracture toughness with increasing temperature which accelerated wear because of the debris generated. It was confirmed that at process temperature of over than 100 oC, the bond structure of the carbon film changed, and the effect of excellent internal stress was reduced. However, the wear resistance simultaneously decreased owing to the reduction in fracture toughness. Therefore, in order to increase industrial utilization, optimum temperature conditions that reduce internal stress and retain mechanical properties.","filtered cathode vacuum arc(자장여과아크플라즈마), tetrahedral amorphous carbon(사면체 비정질 카본), process temperature(공정온도), Hardness(경도), friction(마찰), wear(마멸)","강용진1ㆍ김도현1ㆍ류호준2ㆍ김종국3ㆍ장영준1†\n1한국기계연구원부설 재료연구소 표면기술연구본부 극한환경코팅연구실 선임연구원, 2한국기계연구원부설 재료연구소 표면기술연구본부 극한환경코팅연구실 학생연구원, 3한국기계연구원부설 재료연구소 표면기술연구본부 극한환경코팅연구실 책임연구원","https://doi.org/10.9725/kts.2019.35.6.362"]
["35권6호\npp.369-375","헤드 램프 빛의 각도 자동 조절 장치에 작용하는 추력의히스테리시스에 대한 마찰의 영향\n(Effect of Friction on the Hysteresis of the Thrust Forces Acting on Auto Leveling Devices in Vehicle Head Lamps)","Automotive Tribology","This paper presents a new method on how to calculate the thrust forces acting on an auto-leveling device in headlamps for passenger vehicles. The leveling device is used to lower the angle of lights when a load in the trunk of the vehicle lifts it. In the process of the headlamp design, it is imperative to predict the external forces so that the designers can decide whether to proceed or not. The device is composed of three pivot joints with no reaction moment, a plate that holds the lamp, and a leveling motor that changes rotation to linear motion. In this study, force balance, moment balance, and geometric compatibility are applied to the leveling device system so that a nonlinear system of equations can be derived; the multi-dimensional Newton-Raphson algorithm is then used to solve these. A sensitivity analysis is carried out to verify which design variables affect the system the most: the mass of the lamp and the height between the pivot and leveling device affect the thrust forces the most. Then, considering the friction forces between the moving parts, the hysteresis of the forces are derived. An experimental apparatus, designed and developed in this study, is used to verify the exactness of the derived equations. The results from experiments coincide well with the calculated results. The friction hysteresis, in particular, proves this upon analysis.","auto leveling device(자동 각도 조절 장치), head lamp(헤드램프), thrust force(추력), friction(마찰), hysteresis(히스테리시스)","백 홍1ㆍ김재훈2ㆍ남진식3ㆍ박상신4†\n1영남대학교 대학원 기계공학과 석사과정생, 2영남대학교 기계공학부 학사과정생, 3㈜SL 전장부품설계팀 책임연구원, 4영남대학교 기계공학부 교수","https://doi.org/10.9725/kts.2019.35.6.369"]
["35권6호\npp.376-381","미세 그루브가 있는 무한폭 Slider 베어링의 윤활해석:제1보 - 그루브 위치의 영향\n(Lubrication Analysis of Infinite Width Slider Bearing witha Micro-Groove: Part 1 - Effect of Groove Position)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Surface texturing is widely applied to reduce friction and improve the reliability of machine elements. Despite extensive theoretical studies to date, most research has been limited to parallel thrust bearings, mechanical face seals, piston rings, etc. However, most sliding bearings have a convergent film shape in the sliding direction and the hydrodynamic pressure is mainly generated by the wedge action. The results of surface texturing on inclined slider bearings are largely insufficient. This paper is the first part of a recent study focusing on the effect of the groove position on the lubrication performances of inclined slider bearings. We model a slider bearing with one rectangular groove on a fixed pad and analyze the continuity and Navier–Stokes equations using a commercial computational fluid dynamics (CFD) code, FLUENT. The results show that the film convergence ratio and the groove position have a significant influence on the pressure and velocity distributions. There are groove positions to maximize the supporting load with the film convergence ratio and the groove reduces the frictional force acting on the slider. Therefore, the proper groove position not only improves the load-carrying capacity of the slider bearings but also reduces its frictional loss. The present results apply to various surface-textured sliding bearings and can lead to further studies.","slider bearing(슬라이더 베어링), surface texturing(표면조직가공), Navier–Stokes equation(나비에-스톡스 방정식), hydrodynamic lubrication(유체윤활), numerical analysis(수치해석)","박태조1†ㆍ장인규2\n1경상대학교 기계공학부 · 공학연구원, 2경상대학교 기계항공정보융합공학부 학부생","https://doi.org/10.9725/kts.2019.35.6.376"]
["35권6호\npp.382-388","미세 그루브가 있는 무한폭 Slider 베어링의 윤활해석:제2보 - 그루브 깊이의 영향\n(Lubrication Analysis of Infinite Width Slider Bearing witha Micro-Groove: Part 2 - Effect of Groove Depth)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","It is currently well known that surface textures act as lubricant reservoirs, entrap wear debris, and hydrodynamic bearings, which can lead to certain increases in load-carrying capacities. Until recently, the vast majority of research has focused on parallel sliding machine components such as thrust bearings, mechanical face seals, piston rings, etc. However, most sliding bearings have a convergent film shape in the sliding direction and their hydrodynamic pressure is mainly generated by the wedge action. Following the first part of the present study that investigates the effect of groove position on the lubrication performances of inclined slider bearings, this paper focuses on the effects of groove depths and film thicknesses. Using a commercial computational fluid dynamics (CFD) code, FLUENT, the continuity and Navier–Stokes equations are numerically analyzed. The results show that the film thickness and groove depth have a significant influence on the pressure distribution. The maximum pressure occurs at the groove depth where the vortex is found and, as the depth increases, the pressure decreases. There is also a groove depth to maximize the supporting load with the film thickness. The friction force acting on the slider decreases with deeper grooves. Therefore, properly designed groove depths, depending on the operating conditions, can improve the load-carrying capacity of inclined slider bearings as compared to the bearings without a groove.","slider bearing(슬라이더 베어링), surface texturing(표면조직가공), Navier–Stokes equation(나비에-스톡스 방정식), hydrodynamic lubrication(유체윤활), numerical analysis(수치해석)","박태조1†ㆍ장인규2\n1경상대학교 기계공학부 · 공학연구원, 2경상대학교 기계항공정보융합공학부 학부생","https://doi.org/10.9725/kts.2019.35.6.382"]
["35권6호\npp.389-395","대기압/진공 조건의 트라이보 시험기를 이용한 박막 코팅의 마찰/마모 특성 비교\n(Comparison of Friction and Wear Characteristics of Thin Film Coatings Using Tribotesters at Atmospheric/Vacuum Conditions)","Tribo-Testing / Measurement & Instruments ,Contact Mechanics & Friction ,Wear Phenomena & Mechanisms","In various industries, thin film coatings are used to improve friction and wear characteristics. Various types of tribotesters are used to evaluate the friction and wear characteristics of such thin film coatings. In this study, we fabricated a micro-tribotester and Tribo-scanning electron microscopy (SEM) to compare the friction and wear characteristics of copper (Cu) coatings under an atmospheric pressure and a vacuum condition, respectively. The reliability of the different types of tribotesters was evaluated by performing calibrations for the sensor to measure the friction forces and normal loads. Using the two different types of devices, the friction and wear tests are conducted at the same experimental conditions excluding environment conditions such as the atmospheric pressure and vacuum condition. The friction coefficient at the vacuum condition is lower than at the atmospheric pressure. This difference in friction characteristics is due to the fact that wear phenomena occur differently according to the atmospheric pressure and vacuum condition. At the atmospheric pressure, the abrasive wear is the main wear mechanism. At the vacuum condition, the adhesive wear is the main wear mechanism. The reason for the difference in the wear mechanism of the Cu coating at the atmospheric pressure and the vacuum condition is that the oxidation phenomenon, which does not appear at the vacuum condition, occurs at the atmospheric pressure; therefore, the characteristics of the Cu coating change accordingly.","atmospheric pressure(대기압), coating(코팅), friction(마찰), vacuum(진공), wear(마모)","김해진1ㆍ김대은2ㆍ김창래3†\n1경상대학교 기계항공공학부 조교수, 2연세대학교 기계공학과 교수, 3조선대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2019.35.6.389"]
["35권6호\npp.396-402","Friction Characteristics of Aluminized Polyester Fabric under Dry- and Water- Lubricated Conditions","Contact Mechanics & Friction","Materials made from plastics are increasingly utilized in constructing greenhouses and setting up shield structures. Polyester fabrics have a wide range of use in horticulture and other fields of agriculture. They are utilized as a greenhouse cover and also help in combating intense climate variation in the field. Over time, these fabrics may experience friction against other surfaces. Owing to this, the surface framework of the material degenerates. This study examines the frictional characteristics of aluminized polyester fabric in both dry- and water-lubricated environments under changing applied loads and sliding speeds. Friction experiments are performed at room temperature by employing a pin on a disk. The experiments reveal that the friction coefficient decreases with increase in applied load in both dry sliding and water-lubricated environment. However, the friction coefficient decreases more under the water-lubricated setting than in the dry state. At the maximum applied load, the highest friction coefficient is discovered in the dry state with a range of 0.282 to 0.237, whereas a friction coefficient of 0.229 to 0.189 is observed in the water-lubricated state. Additionally, it is observed that the friction coefficient increases with an increase in sliding speed under both experimental environments. The examination of specimen surfaces reveals that the abrasion is minor in the water-lubricated setting compared with that in the dry state.","abrasion, aluminum, friction coefficient, greenhouse, polyester","JaeYoung Byun1, Nicholas Nnaemeka Okechukwu2, Eunsuk Lee1, JinGyu Park3 and WonSik Choi4†\n1Ph.D. Student, Graduate School, Dept. of Bio-Industrial Machinery Engineering, Pusan National University, 2M.S. Student, Graduate School, Dept. of Bio-Industrial Machinery Engineering, Pusan National University, 3CEO, JEONG-IL GLOCHEM CO., LTD., 4Professor, Dept. of Bio-Industrial Machinery Engineering, Pusan National University","https://doi.org/10.9725/kts.2019.35.6.396"]

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["권호","제목","토픽","초록","키워드","저자","DOI"]
["36권1호\npp.1-10","A Review on Transfer Process of Two-dimensional Materials","Micro/Nano-Tribology ,Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","Large-area two-dimensional (2D) materials synthesized by chemical vapor deposition on donor substrates are promising functional materials for conductors, semiconductors, and insulators in flexible and transparent devices. In most cases, 2D materials should be transferred from a donor substrate to a target substrate; however, 2D materials are prone to damage during the transfer process. The damages to 2D materials during transfer are caused by contamination, tearing, and chemical doping. For the commercialization of 2D materials, a damage-free, large-area, and productive transfer process is needed. However, a transfer process that meets all three requirements has yet to be developed. In this paper, we review the recent progress in the development of transfer processes for 2D materials, and discuss the principles, advantages, and limitations of each process. The future prospects of transfer processes are also discussed. To simplify the discussion, the transfer processes are classified into four categories: wet transfer, dry transfer, mechanical transfer, and electrochemical transfer. Finally, the “roll-to-roll” and “roll-to-plate” dry transfer process is proposed as the most promising method for the commercialization of 2D materials. Moreover, for successful dry transfer of 2D materials, it is necessary to clearly understand the adhesion properties, viscoelastic behaviors, and mechanical deformation of the transfer film used as a medium in the transfer process.","2D materials, transfer process, chemical-vapor deposition","Chan Kim1,4, Min-Ah Yoon1,4, Bongkyun Jang5, Jae-Hyun Kim3,6 and Kwang-Seop Kim2,5†\n1Ph.D. Student, Dept. of Nano-Mechatronics, University of Science and Technology (UST), 2Associate Professor, Dept. of Nano-Mechatronics, University of Science and Technology (UST), 3Professor, Dept. of Nano-Mechatronics, University of Science and Technology (UST), 4Researcher, Nano-Convergence Mechanical System Research Division, Korea Institute of Machinery & Materials (KIMM), 5Senior Researcher, Nano-Convergence Mechanical System Research Division, Korea Institute of Machinery & Materials (KIMM), 6Principal Researcher, Nano-Convergence Mechanical System Research Division, Korea Institute of Machinery& Materials (KIMM)","https://doi.org/10.9725/kts.2020.36.1.1"]
["36권1호\npp.11-17","Friction Assessment of Canola Oil on Contact Bearing Materials","Lubrication (Lubricants & Additives) ","In manufacturing operations, oil plays a crucial role in reducing friction and wear among interacting surfaces at varying velocities, loads, and temperature. Hydrocarbon oil is considered the origin of lubrication oils. However, this base oil has been limited in its use as it is a principal cause of pollution. This research focuses on identifying a biodegradable base oil lubricant that possesses a stable coefficient of friction and viscosity with temperature. Friction analysis is conducted by employing a pin on a disk tribotester with a fixed load of 10 N at varying sliding speeds ranging from 0.06 m/s to 0.34 m/s. Oil viscosity analysis is perfomed at room temperature by using a rotary viscometer. Tests are performed using canola oil and paraffin oil as lubricants. The results indicate that the viscosity of canola oil is more efficient than paraffin oil. The non-dimensional characteristic number according to the Stribeck curve reveals an elastohydrodynamic lubrication regime with canola oil lubrication. A comparison of both lubricants reveals that, the friction efficiency of canola oil and paraffin oil does not differ considerably. However, the friction in canola oil is observed to decrease more than that in paraffin oil at an elevated sliding speed. The tests confirm that canola oil is potent in minimizing the friction coefficient of SCM440 bodies interacting with one another as well as acted upon by load.","canola oil, elastohydrodynamic lubrication, friction, stribeck curve, viscosity","Nicholas Nnaemeka Okechukwu1, JaeYoung Byun2, JongSoon Kim3, JongMin Park3,SoonGoo Kwon3, SungWon Chung3, SoonHong Kwon3 and WonSik Choi3†\nUniversity, 2Ph.D. Student, Graduate School, Dept. of Bio-Industrial Machinery Engineering, Pusan National University, 3Professor, Dept. of Bio-Industrial Machinery Engineering, Pusan National University","https://doi.org/10.9725/kts.2020.36.1.11"]
["36권1호\npp.18-26","침탄처리한 SCM420H의 미끄럼 마모 특성에 미치는 침탄 조건의 영향\n(Effects of Carburizing Process on Sliding wear Behaviorof Carburized SCM420H Steel)","Tribology in Design & Manufacturing (Metalworking / Machining) ","The effects of the carburizing process on the sliding wear behavior of SCM420H steel have been inves\uffffﾠ\uffffﾠ\ntigated. In particular, the effects of grain boundary corrosion observed in the surface layer after gas carburizing and the effects of hardness of the carburized cases after heat-treatment on the sliding wear properties were examined. Pin specimens carburized by two methods (gas carburizing and vacuum carburizing) were tempered at two temperatures of 180℃ and 400℃ after oil-quenching, respectively. Sliding wear tests were carried out against heat- treated SKH51 steel at several sliding speeds using a pin-on-disc type test machine. As results, it can be found that there is no difference in the wear behavior between the pins carburized using two methods. This implies that the grain boundary corrosion that formed in the surface layer after gas carburizing has no effect on the sliding wear behavior of carburized SCM420H steels. Additionally, there is no significant difference in the wear behavior between carburized pins tempered at 400℃ and at 180℃ after oil-quenching, regardless of the carburizing method. This is because carburized pins tempered at 400℃ have a troostite structure, which exhibits higher tribochemical reactivity even though its hardness is lower than that of martensite structure. In this respect, it can be considered that good wear resistance of carburized cases is maintained at least until the effective case depth.","gas carburizing(가스침탄), vacuum carburizing(진공침탄), grain boundary corrosion(입계산화), sliding wear behavior(미끄럼마모거동), hardness(경도)","이한영1†ㆍ이규헌2\n1계명대학교 신소재공학과 교수, 2계명대학교 대학원 재료공학과 석사졸업생","https://doi.org/10.9725/kts.2020.36.1.18"]
["36권1호\npp.27-33","자려 평형 틸팅 패드 스러스트 베어링의 정렬불량에 따른 베어링 특성에 관한 실험적 연구\n(Experimental Study on the Characteristics of MisalignedSelf-equalizing Tilting Pad Thrust Bearing)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Self-equalizing tilting pad thrust bearings are usually employed in turbomachines to achieve high stability and reliability. A tilting pad bearing can incorporate self-equalizing links to handle the misalignment between the bearing and the thrust collar. In this popular design method, the pads sit on the upper-level plates and the lower-level plates stay on the retainer base. With misalignment, the pads that are heavily loaded are pushed down. Consequently, the link pushes up the pads on the opposite side, keeping the bearing surface parallel to the thrust collar surface. The self-equalizing link is used to handle the misalignment from the thermal and mechanical effects. In this study, the experimental investigation deals with the performance of self-equalizing tilting pad thrust bearings. The test rig for evaluating the performance of bearing is developed which can control the misalignment angle. Simultaneous measurements are taken for the force acting on each pad. Pad metal temperature and oil film thickness are functions of the shaft speed, bearing load, misalignment angle, and design of leveling plates. The effect of misalignment on bearing performance is discussed. The results demonstrate that the load on each pad depends on the test conditions(especially misalignment angle), and the load influences the performance of bearings.","self-equalizing(자동 정렬), tilting pad thrust bearing(틸팅 패드 스러스트 베어링), misalignment(정렬불량), unit load(면압), temperature(온도), oil film thickness(유막 두께)","송애희1ㆍ조현준1ㆍ최성필1†ㆍ김선진2\n1(주)터보링크 기술연구소 연구원, 2부경대학교 기계설계공학과 교수","https://doi.org/10.9725/kts.2020.36.1.27"]
["36권1호\npp.34-38","특수 목적 차량의 수상 추진체용 카단 샤프트의 유니버셜 조인트에 대한 응력 및 수명 평가\n(Stress and Life Evaluation of Universal Joint of Cardan Shaftfor Waterjet System of Special-Purpose Vehicle)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","The powertrain of the waterjet system of a special-purpose vehicle makes use of the cardan shaft, which is composed of universal joints and shafts. These universal joints, composed of spiders and needle roller bearings, have to be designed with consideration for the bending and compressive stresses of the spiders and needle roller bearings, and the rating lives of the bearings. The bending and compressive stresses of the spider and bearing of a universal joint have been studied by many researchers. However, to design a universal joint effectively, overall consideration of the different specifications of needle roller bearings is necessary. In this study, the bending stresses of spiders and compressive stresses of needle roller bearings are calculated to design universal joints for powertrain cardan shafts with different roller diameters of bearing. Furthermore, the rating lives of the needle roller bearings are predicted using the calculated basic dynamic load ratings of the bearings. As a result, roller diameters less than φ2.5 mm are found suitable through an analysis of the bending stress of the spider. All compressive stresses between spider and bearing, regardless of roller diameter, satisfy the requirements. Moreover, roller diameters of more than φ2 mm are found suitable for the required rating life.","universal joint(유니버셜 조인트), spider(스파이더), needle roller bearing(니들 롤러 베어링), bending stress(굽힘응력), compressive stress(면압응력), rating life(정격수명)","배명호1ㆍ이태영2ㆍ조연상3†\n1창원문성대학교 항공정비과 부교수, 2카템 대표이사, 3동아대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2020.36.1.34"]
["36권1호\npp.39-46","에어 스테이지의 동적 특성에 미치는 가속도 및 감속도의 영향\n(Effect of the Acceleration and Deceleration on the Dynamic Characteristics of an Air Stage)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Air stages are usually applied to precision engineering in sectors such as the semiconductor industry owing to their excellent performance and extremely low friction. Since the productivity of a semiconductor depends on the acceleration and deceleration performance of the air stage, many attempts have been made to improve the speed of the stage. Even during sudden start or stop sequences, the stage should maintain an air film to avoid direct contact between pad and the rail. The purpose of this study is to quantitatively predict the dynamic behavior of the air stage when acceleration and deceleration occur. The air stage is composed of two parts; the stage and the guideway. The stage transports objects to the guideway, which is supported by an externally pressurized gas bearing. In this study, we use COMSOL Multiphysics to calculate the pressure of the air film between the stage and the guideway and solve the two-degree-of-freedom equations of motion of the stage. Based on the specified velocity conditions such as the acceleration time and the maximum velocity of stage, we calculate the eccentricity and tilting angle of the stage. The result shows that the stiffness and damping of the gas bearing have non-linear characteristics. Hence, we should consider the operating conditions in the design process of an air stage system because the dynamic behavior of the stage becomes unstable depending on the maximum velocity and the acceleration time.","air bearing stage, dynamic analysis, acceleration, deceleration, COMSOL","박상준1ㆍ이재혁1ㆍ박상신2†ㆍ김규하3\n1영남대학교 대학원 기계공학과 석사과정생, 2영남대학교 기계공학부 교수, 3㈜트리엔 기술연구소 소장","https://doi.org/10.9725/kts.2020.36.1.39"]
["36권1호\npp.47-53","Selective Laser Melting 방식으로 적층가공된 Ti-6Al-4V 합금의 내마모성 특성에 미치는 고온 UNSM 처리 영향에 대한 연구\n(Effects of High-temperature UNSM Treatment on Wear Resistance of Ti-6Al-4V Alloy Prepared by Selective Laser Melting)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT of 400oC) on friction and wear behavior of Ti-6Al-4V alloy prepared by selective laser melting (SLM) were investigated. The objective of this study is to improve the mechanical properties and frictional behavior of Ti-6Al-4V alloy by UNSM treatment. Dry friction and wear tests were conducted using a ball-on-disk method at RT with a bearing steel as the counter ball. Due to the high HT and UNSM treatment, the surface hardness tended to increase and surface roughness tended to reduce. X-ray diffraction (XRD) analysis showed that nanocrystallization structure and compressive residual stress were formed at the surface layer after UNSM treatment at both RT and HT. After UNSM treatment, it was observed that the wear rate was reduced by about 6% for the specimen treated at RT and a 28% reduction for the specimen treated at HT in comparison with the untreated one. Based on scanning electron microscope (SEM) images showed that the damage caused by fatigue wear occurred in the wear track of the heat-treated specimen, and it is believed to be the cause of the highest wear rate. Mechanical properties and wear resistance of Ti-6Al-4V alloy were improved and prospect of industrial application was confirmed. Further research is still required to improve the characteristics of SLM Ti-6Al-4V alloy to the level of wrought Ti-6Al-4V alloy.","additive manufacturing(적층가공), Ti-6Al-4V alloy(Ti-6Al-4V 합금), surface roughness(표면거칠기), wear resistance(내마모성), ultrasonic nanocrystal surface modification(초음파 나노표면개질)","산성충호1ㆍ노준석1ㆍ편영식2ㆍ아마노프 아웨즈한3†\n1선문대학교 대학원 융합과학기술학과 석사과정생, 2선문대학교 융합과학기술학과 명예교수, 3선문대학교 기계공학과 부교수","https://doi.org/10.9725/kts.2020.36.1.47"]
["36권2호\npp.55-63","트라이볼로지 관점에서의 그래핀 분자시뮬레이션 연구동향\n(Review on Molecular Simulation of Graphene from a Tribological Perspective)","Micro/Nano-Tribology","Recently, graphene has attracted considerable attention owing to its unique electrical, optical, thermal, and mechanical properties. The broad spectrum of applications from optics, sensors, and electronics to biodevice have been proposed based on these properties. In particular, graphene has been proposed as a protective coating layer and solid lubricant for microdevices and nanodevices because of its high mechanical strength, chemical inertness, and low friction characteristics. During the past decade, extensive efforts have been made to\nexplore the tribological characteristics of graphene under various conditions and to expand its applicability. In addition to the experimental approaches, the molecular simulations performed provide fundamental insights into the friction and wear characteristics of graphene resulting from molecular interactions. This work is a review of the studies conducted over the past decade on the tribological characteristics of graphene using molecular simulation. These studies demonstrate the principal mechanisms of the superlubricity of graphene and help clarify the influences of surface conditions on tribological behavior. In particular, the investigation of the effects of the\nnumber of layers, strength of adhesion to the substrate, surface roughness, and commensurability provides deeper insights into the tribological characteristics of graphene. These fundamental understandings can help elucidate the feasibility of graphene as a protective coating layer and solid lubricant for microdevices and nanodevices.","molecular simulation(분자 시뮬레이션), graphene(그래핀), nano-scale friction(나노스케일 마찰), numerical analysis(수치해석)","김현준1ㆍ정구현2†\n1경북대학교 정밀기계공학과 부교수, 2울산대학교 기계공학부 교수","https://doi.org/10.9725/kts.2020.36.2.55"]
["36권2호\npp.64-67","핀치형 내부로터의 제로터 설계\n(Design of Gerotor with Pin-tooth Inner Rotor)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In the conventional gerotor design, the circular arc tooth of the outer rotor is first introduced, and\nthen the inner rotor profile is generated by simulating the outer rotor motion while the inner rotor is fixed. The profile generation of tooth meshing exhibits relativity; therefore, the outer rotor profile can be generated by the movement of the inner rotor. In this study, we propose the design of a gerotor with a pin-tooth inner rotor. First, the pin-tooth inner rotor is devised, and then the outer rotor profile is generated. The profile of the inner rotor is simply composed of equally arranged pins along a circle. The root of the inner rotor is designed as a conjugated arc of two pins. The trajectory of the pin center is obtained by the inner rotor operation, and then the outer rotor profile is determined as a parallel curve of the trajectory. In this gerotor design, the inner rotor has a simple configuration, and contact occurs between the pin parts of the inner rotor and the whole profile of the outer rotor. This affects the material selection and machining process. The pin tooth can be used to design the outer and inner rotors, enabling a double gerotor mechanism corresponding to a planetary gear system.","gerotor(제로터), pin tooth(핀치형), planetary mechanism(유성기구), Tooth generation(치형창성)","이성철†\n인하공업전문대학 기계과 교수","https://doi.org/10.9725/kts.2020.36.2.64"]
["36권2호\npp.68-74","공기 스테이지의 형상 오차가 운동정밀도에 미치는 영향\n(Effect of Shape Error of an Air Stage on Motion Precision)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In this study, the effect of the shape error of a guideway on the movement of a stage that uses an air bearing is analyzed. The shape error of moving parts supported by the air bearing is known not to affect the vibrations of moving parts as much as the magnitude of the shape error. This is called the “averaging effect.” In this study, the effect of shape error on a guideway, as well as the averaging effect of an air-bearing system, is analyzed theoretically using a dynamic-analysis program. The dynamic-analysis program applies a commercially\navailable code in COMSOL and solves the Reynolds equation between the stage and the guideway, along with the equation of motion of the stage. The stage is modeled as a two-degree-of-freedom system. The shape error is applied to the film thickness function in the form of a sine wave. The stage movement is analyzed using the fast Fourier transform process. The eccentricity and tilting are found to be proportional to the amplitude of the shape error of the guideway. Stage vibrations are less than 10% of the amplitude of the shape error on the guideway. This means that the averaging effect of the air bearing is verified quantitatively. Moreover, if the air supply position matches the shape error in the guideway, there is a notable change in eccentricity and tilting.","air-bearing stage(공기베어링 스테이지), shape error(형상 오차), averaging effect(평균화 효과)","류대원1ㆍ이재혁1ㆍ박상신2†ㆍ김규하3\n1영남대학교 대학원 기계공학과 석사과정생, 2영남대학교 기계공학부 교수, 3 ㈜트리엔 기술연구소 소장","https://doi.org/10.9725/kts.2020.36.2.68"]
["36권2호\npp.75-81","누설 저감을 위한 75톤급 터보펌프 개량형 미케니컬페이스실 개발\n(Development of Mechanical Face Seal in 75-tonf Turbopumpfor Leakage Reduction)","Space/Extreme Tribology","In this paper, we present an experimental investigation of the leakage and endurance performances of mechanical face seals in a 75-tonf turbopump for the Korea Space Launch Vehicle II first-stage engine. A mechanical face seal is used between the fuel pump and turbine to prevent mixing of the fuel and turbine gas. However, excessive leakage occurs through the carbon attached to the mechanical face seal bellows. To reduce this leakage, we redesign the mechanical face seal such that the contact area between the fuel and carbon is reduced, height of the carbon nose is reduced, and stiffness of the bellows is increased. Then, we conduct static and dynamic leakage tests and endurance tests to compare the performances of the original and modified mechanical face seals. The investigation of the leakage of the old and new mechanical face seals confirms that the leakage performance is significantly improved, by 80%, in the new design in comparison with the old design. The endurance tests demonstrate that the average wear rate of carbon in the new mechanical face seal is 0.1094 μm/s. The service lifetime is predicted to be 4,200 s, which is 28 times greater than the requirement. Finally, we present a new mechanical face seal in a 75-tonf turbopump, and perform a validation test in the real-propellant test facility at the NARO Space Center. Based on the test results, we can confirm that the modified mechanical face seal works well under real operating conditions.","turbopump(터보펌프), mechanical face seal(미케니컬 페이스 실), wear rate(마모율), leakage(누설), performance test(성능 시험)","배준환1,2ㆍ곽현덕3ㆍ이창훈4ㆍ최종수5†\n1한국항공우주연구원 터보펌프팀 선임연구원, 2충남대학교 항공우주공학과 박사과정생, 3한국항공우주연구원 터보펌프팀 책임연구원, 4한국씰마스타(주) 미케니컬실 기술개발팀 대리, 5충남대학교 항공우주공학과 정교수","https://doi.org/10.9725/kts.2020.36.2.75"]
["36권2호\npp.82-87","정렬불량에 따른 틸팅 패드 스러스트 베어링의운전 성능 한계 검토\n(Operating Performance Limitations of Tilting Pad ThrustBearings Due to Misalignment)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In thrust bearings, the thrust collar and bearing surface need to be parallel to each other to ensure that all pads share the same load. In rotating machines, the shaft system cannot achieve perfect alignment. Misalignment of the thrust collar results in some pads supporting a higher load than others and excessive loads being placed on some pads. Consequently, high loads and high temperatures may occur in the bearing. Thus, in this study, we aim to analytically evaluate the performance of a misaligned non-equalizing direct lubricated tilting pad thrust bearing. We define the oil film thickness of the misaligned thrust bearing using the Byrant angle. Additionally, we calculate the pressure distribution and temperature distribution of the thrust bearing using the generalized Reynolds equation and energy equation. The design limit of the thrust bearing is defined by the load and temperature. Therefore, we evaluate the allowable misalignment angle as the limit of the maximum load and temperature. The analysis results demonstrate that an increase in the speed and load corresponds to a smaller allowable misalignment angle. However, as this is not the same for all thrust bearings, evaluating the allowable misalignment angle at each thrust bearing is essential.","thrust bearing(스러스트 베어링), misalignment(정렬불량), surface speed(표면 속도), unit load(단위 하중)","송애희1†ㆍ최성필1ㆍ김선진2\n1(주)터보링크 기술연구소 연구원, 2부경대학교 기계설계공학과 교수","https://doi.org/10.9725/kts.2020.36.2.82"]
["36권2호\npp.88-95","자동차용 브레이크 마찰재에서 고망간강의 마찰 및 마모특성\n(Friction and Wear Properties of High Manganese Steel in Brake Friction Material for Passenger Cars)","Others","In this study, we investigate the mechanical properties of high manganese steel, and the friction and wear characteristics of brake friction material containing this steel, for passenger car application, with the aim of replacing copper and copper alloys whose usage is expected to be restricted in the future. These steels are prepared using a vacuum induction melting furnace to produce binary and ternary alloys. The hardness and tensile strength of the high manganese steel decrease and the elongation increases with increase in manganese content. This material exhibits high values of hardness, tensile strength, and elongation; these properties are similar to those of 7-3 brass used in conventional friction materials. We fabricate high manganese steel fibers to prepare test pad specimens, and evaluate the friction and wear characteristics by simulating various braking conditions using a 1/5 scale dynamometer. The brake pad material is found to have excellent friction stability in comparison with conventional friction materials that use 7-3 brass fibers; particularly, the friction stability at high temperature is significantly improved. Additionally, we evaluate the wear using a wear test method that simulates the braking conditions in Europe. It is found that the amount of wear of the brake pad is the same as that in the case of the conventional friction material, and that the amount of wear of the cast iron disc is reduced by approximately 10. The high manganese steel is expected to be useful in the development of eco-friendly, copper-free friction material.","1/5 scale dynamometer(1/5 스케일 다이나모미터), cast iron disc(주철디스크), copper free(무동), friction material(마찰재), high manganese alloy(고망간강)","정광기1,3ㆍ이상우2†ㆍ권성욱3ㆍ송명석3\n1금오공과대학교 대학원 신소재공학과 박사과정, 2금오공과대학교 신소재공학부 정교수, 3상신브레이크 기술연구소 연구원","https://doi.org/10.9725/kts.2020.36.2.88"]
["36권2호\npp.96-104","전기자동차용 2속 변속기의 경량 최적 설계\n(Optimal Design of Lightweight Two-Speed Transmissionof Electric Vehicles)","Automotive Tribology","The electric vehicle industry is rapidly developing because of enforced environmental regulations, and several studies have been conducted on the multispeed transmission to improve the fuel efficiency of electric vehicles. Among these studies, research on the power density improvement of electric vehicle transmission is critical. Thus, the optimal design of the gear train is necessary to enhance transmission efficiency. In this study, an optimal design methodology for the lightweight two-speed transmission of electric vehicles is proposed. Because a multispeed transmission has many operating conditions and equality and inequality constraints, a new gear design method that combines analytical and iterative methods is applied without using complex optimization algorithms. Sets of possible design variables are generated considering the operating conditions and various design variables. The modules and face width ratios of each stage gear that satisfy the corresponding operating conditions are analytically calculated. The volume of the gear train is calculated, evaluated, and arranged using these values to determine the optimal solution for minimizing the volume, and the proposed methodology is applied to the actual model to verify its effectiveness. The design of a two-speed transmission with multiple operating conditions and constraints without complicated optimization algorithms can be optimized.","gearbox(기어박스), transmission(변속기), optimal design(최적설계), electric vehicle(전기자동차)","최재훈1ㆍ서준호2†ㆍ박노길3\n1부산대학교 기계공학부 대학원 석사과정생, 2부산대학교 기계공학부 조교수, 3부산대학교 기계공학부 교수","https://doi.org/10.9725/kts.2020.36.2.96"]
["36권2호\npp.105-115","블레이드 손상에 따른 이축식 터보팬 엔진의 동적 안정성 해석\n(Rotordynamic Analysis of a Dual-Spool Turbofan Enginewith Focus on Blade Defect Events)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","This paper presents a numerical study on the rotordynamic analysis of a dual-spool turbofan engine in the context of blade defect events. The blades of an axial-type aeroengine are typically well aligned during the compressor and turbine stages. However, they are sometimes exposed to damage, partially or entirely, for several operational reasons, such as cracks due to foreign objects, burns from the combustion gas, and corrosion due to oxygen in the air. Herein, we designed a dual-spool rotor using the commercial 3D modeling software CATIA to simulate blade defects in the turbofan engine. We utilized the rotordynamic parameters to create two finite element Euler–Bernoulli beam models connected by means of an inter-rotor bearing. We then applied the unbalanced forces induced by the mass eccentricities of the blades to the following selected scenarios: 1) fully balanced, 2) crack in the low-pressure compressor (LPC) and high pressure compressor (HPC), 3) burn on the high-pressure turbine (HPT) and low pressure compressor, 4) corrosion of the LPC, and 5) corrosion of the HPC. Additionally, we obtained the transient and steady-state responses of the overall rotor nodes using the Runge–Kutta numerical integration method, and employed model reduction techniques such as component mode synthesis to enhance the computational efficiency of the process. The simulation results indicate that the high-vibration status of the rotor commences beyond 10,000 rpm, which is identified as the first critical speed of the lower speed rotor. Moreover, we monitored the unbalanced stages near the inter-rotor bearing, which prominently influences the overall rotordynamic status, and the corrosion of the HPC to prevent further instability. The high-speed range operation (>13,000 rpm) coupled with HPC/HPT blade defects possibly presents a rotor–case contact problem that can lead to catastrophic failure.","turbofan engine(터보팬 엔진), blade defect(블레이드 손상), dual-spool rotor(이축식 로터), rotordynamics(로터동역학)","김시태1†ㆍ정기현2ㆍ이준호2ㆍ박기현2ㆍ양광진3\n1공군사관학교 기계공학과 부교수, 2공군사관학교 기계공학과 학부과정생, 3공군사관학교 기계공학과 정교수","https://doi.org/10.9725/kts.2020.36.2.105"]
["36권3호\npp.117-123","미끄럼 속도변화에 따른 철강재료의 미끄럼 마모거동(중마모 거동에 미치는 연마모 도입시험의 영향)\n(Sliding Wear Behavior of Carbon Steel in changing Sliding Speed (Effects of Mild Wear Mode Test on subsequent Severe Wear Behavior))","Wear Phenomena & Mechanisms","In this study, the effect of the pre-mild wear mode test condition on the subsequent severe wear behavior of carbon steel has been investigated when the wear mode is varied according to the sliding speed change during sliding contact. Two sliding speeds of 0.3 m/s and 3 m/s for the mild wear mode test have been chosen and a sliding speed of 1 m/s for the severe wear mode test. A mild wear mode test at two different sliding speeds has been carried out during the severe wear mode test and total sliding distance of the mild wear mode test has been changed at this time. As a result, it could be found that the wear rate of carbon steel under the severe wear mode test after performing a pre-mild wear mode test is significantly reduced, compared with that before performing. However, its wear rate was slightly higher than that under the mild wear mode test. Oxides produced during the pre-mild wear mode test have been found to play a significant role in reducing the wear rate under the subsequent severe wear mode test. In particular, it was found that the effect of a pre-mild wear mode test performed at the sliding speed of 3 m/s has more rapid and the reduction in the wear rate was greater than thst at the sliding speed of 0.3 m/s.","mild wear(연마모), severe wear(중마모), changing speed(속도변화), carbon steel(탄소강), sliding wear(미끄럼 마모)","이한영†\n계명대학교 신소재공학과 교수","https://doi.org/10.9725/kts.2020.36.3.117"]
["36권3호\npp.124-132","연소합성 코팅된 NiAl 금속간화합물의 화학양론이미끄럼 마모특성에 미치는 영향\n(Effects of Stoichiometry on Properties of NiAl Intermetallics coated on Carbon Steel through Combustion Synthesis)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","The effect of the stoichiometry on the sliding wear properties of NiAl coatings has been investigated. Three different powder mixtures with the compositions of Ni-50at%Al, Ni-54at%Al and Ni-42at%Al were die-pressed respectively, and which were subsequently coated on mild steel through combustion synthesis in an induction heating system. Sliding wear behavior of the coatings was examined against an alloyed tool steel using a pin-on-disc type sliding wear test machine. As results, it could be seen that powder mixture(Ni-54at%Al) with displaying Al-rich deviations from the stoichiometry of NiAl(Ni-50at%Al) was promoted the most the synthetic reactivity. The microstructure of the coating layer with the compositions of Ni-54at%Al exhibits the porous NiAl single phase structure. However, the microstructure of the coating layer of the compositions of Ni-42at%Al exhibits the denser multi-phase structure containing several intermediate phases in addition to NiAl. Densification of the coating layer was enhanced by increasing the reacting temperature. On the other hand, the wear properties of the coating layers showed that the wear mode at speeds of around 1 m/s was severe wear, regardless of the stoichiometry and reacting temperature. However, wear properties of coating layer with the compositions of Ni-42at%Al were superior to those of coating layer with the compositions of Ni-54at%Al. This would be attributed by the fact that coating layer with the compositions of Ni-42at%Al develops little void and much intermediate phases with high strength.","stoichiometry(화학양론), NiAl(NiAl), coating(코팅), sliding wear behavior(미끄럼마모거동), combustion synthesis(연소합성)","이한영1†ㆍ이재성2\n1계명대학교 신소재공학과 교수, 2계명대학교 대학원 재료공학과 석사졸업생","https://doi.org/10.9725/kts.2020.36.3.124"]
["36권3호\npp.133-138","섬유 방향에 따른 에폭시 기반 복합재의 마찰 및 마모 특성에 관한 연구\n(Effect of Fiber Orientation on the Friction and Wear Properties of Epoxy-based Composites)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","In this paper, we present an experimental investigation of the friction coefficient and wear area change of carbon/epoxy and E-glass/epoxy composites depending on the fiber direction (0°/90°). We compared the results of the case where the sliding direction is parallel to the fiber direction (0°) with that of the case where it is perpendicular to the fiber direction (90°). The ball-on-plate wear test equipment was used to cause wear in both directions. Two types of specimens were prepared with thicknesses of 3 mm—one made of carbon fiber reinforced plastic composite (CFRP) and the other of glass fiber reinforced plastic composite (GFRP). A normal force of 20 N was applied to the specimen and the sliding speed was 10 mm/s and the sliding distance was set to 20 m to perform the wear test. The CFRP demonstrates superior tribological characteristics compared to the GFRP. This outcome is attributed to graphitization of carbon, which serves as solid lubricating particles. In addition, both CFRP and GFRP are worn more in the 90° direction than in the 0° direction. This is due to the greater occurrence of fiber breakage and separation in the 90° direction than in the 0° direction. This study is expected to be utilized as basic data for understanding the friction and wear characteristics of CFRP and GFRP composites along the fiber direction and to apply the appropriate material.","carbon/Epoxy composite(탄소섬유 복합재), e-glass/epoxy composite(유리섬유 복합재), fiber orientation(섬유 방향), friction coefficient(마찰 계수), wear(마모)","안효성1ㆍMahdi Khadem2ㆍ전흥재3†ㆍ김대은3††\n1연세대학교 대학원 기계공학과 석사과정생, 2연세대학교 대학원 기계공학과 박사과정생, 3연세대학교 기계공학과 교수","https://doi.org/10.9725/kts.2020.36.3.133"]
["36권3호\npp.139-146","전기 자동차용 폴리올 에스테르계 냉동기유의R-1234yf 냉매와의 적합성 연구\n(Study on Chemical Stabilities with R-1234yf Refrigerantof Polyol Ester Refrigerant Oil for Electric Vehicles)","Lubrication (Lubricants & Additives)","Global warming has led to an increase in demand of eco-friendly vehicles, such as electric cars, for reducing greenhouse gas emissions, and especially, regulating carbon dioxide generation. In addition, electric vehicles are equipped with an electric drive-type hermetic scroll compressor and a refrigerant, which exhibit current and future trends of using environmentally friendly refrigerants, including R-1234yf. In this study, polyol ester-based refrigeration oils are prepared via condensation esterification of polyol and fatty acids. The oils can be combined with R-1234yf refrigerant for applications in air conditioning and cooling systems of electric vehicles. The structure of synthetic polyol esters is confirmed via 1H-NMR and FT-IR spectrum analysis, and the composition of the polyol ester is analyzed via gas chromatogram analysis. Furthermore, kinematic viscosity, viscosity index, total acid value, pour point, and color are analyzed as fundamental physical properties of the synthetic polyol esters. The compatibility and chemical stability of the synthetic polyol ester combined with the R-1234yf refrigerant are obtained via high temperature and high pressure oil-resistant refrigerant tests. The changes in the oil color and catalyst activity are observed before and after the experiment to determine whether it is suitable as a refrigerator oil.","polyol esters(폴리올에스테르), refrigerant oil(냉동기유), R-1234yf refrigerant(R-1234yf 냉매), electric vehicle(전기차)","홍지수1ㆍ정근우2ㆍ김남균3ㆍ신지훈2ㆍ김영운2†ㆍ이은호4ㆍ고봉성5ㆍ황승용6\n1한국화학연구원 화학공정연구본부 연구원, 2한국화학연구원 화학공정연구본부 책임연구원, 3한국화학연구원 화학공정연구본부 선임연구원, 4엔에이치케미칼㈜ 연구소장, 5엔에이치케미칼㈜ 차장, 6한온시스템 부장","https://doi.org/10.9725/kts.2020.36.3.139"]
["36권3호\npp.147-152","응착 완전 접촉 문제에서 접촉면 미끄럼 현상에 관한 고찰\n(On the Slipping Phenomenon in Adhesive Complete Contact Problem)","Contact Mechanics & Friction","This paper is within the framework of an adhered complete contact problem wherein the contact between a half plane and sharp edged indenter, both of which are elastic in character, is constituted. The eigensolutions of the contact shear and normal stresses, σrq and σq, respectively, are evaluated via asymptotic analysis. The ratio of σrq/σqq is investigated and compared with the coefficient of friction, μ, of the contact surface to observe the propensity to slip on the contact surface. Interestingly, there exists a region of |σrθ/σθθ| ≥ |μ|. Thus, slipping can occur, although the problem is solved under the condition of an adhered contact without slipping. Given that a tribological failure potentially occurs at the slipping region, it is important to determine the size of the slipping region. This aspect is also factored in the paper. A simple example of the adhered contact between two elastically dissimilar squares is considered. Finite element analysis is used to evaluate generalized stress intensity factors. Furthermore, it is repeatedly observed that slipping occurs on the contact surface although the size of it is extremely small compared with that of the contacting squares. Therefore, as a contribution to the field of contact mechanics, this problem must be further explained logically.","adhesive complete contact(응착 완전 접촉), slipping behaviour(미끄럼 거동), asymptotic analysis(점근 해석), generalized stress intensity factor(일반 응력확대계수), stress ratio(응력 비)","김형규†\n한국원자력연구원 첨단3D프린팅기술개발부 책임연구원","https://doi.org/10.9725/kts.2020.36.3.147"]
["36권3호\npp.153-160","정압 베어링을 적용한 초임계 CO2 발전용 펌프-구동 터빈 개발\n(Development of Pump-Drive Turbine with Hydrostatic Bearingfor Supercritical CO2 Power Cycle Application)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In this paper, we present a hydrostatic bearing design and rotordynamic analysis of a pump-and-drive turbine module for a 250-kW supercritical CO2 cycle application. The pump-and-drive turbine module consists of the pump and turbine wheel, assembled to a shaft supported by two hydrostatic radial and thrust bearings. The rated speed is 21,000 rpm and the rated power is 143 kW. For the bearing operation, we use high-pressure CO2as the lubricant, which is supplied to the bearing through the orifice restrictor. We calculate the bearing stiffness and flow rate for various orifice diameters, and then select the diameter that provides the maximum bearing stiffness. We also conduct a rotordynamic analysis based on the design parameters of the pump-and-drive turbine module. The predicted Campbell diagram shows that there is no critical speed below the rated speed, owing to the high stiffness of the bearings. Furthermore, the predicted damping ratio indicates that there is no unstable mode. We conduct the operating tests for the pump and drive turbine modules within the supercritical CO2 cycle test loop. The pressurized CO2, at a temperature of 136°C, is supplied to the turbine and we monitor the shaft vibration during the test. The test results show that there is no critical speed below the rated speed, and the shaft vibration is controlled to below 3 μm.","hydrostatic bearing(정압 베어링), supercritical CO2(초임계 이산화탄소)","이동현1†ㆍ김병옥1ㆍ박무룡2ㆍ윤의수2\n1한국기계연구원 시스템다이나믹스연구실 책임연구원, 2한국기계연구원 에너지변환기계연구실 책임연구원","https://doi.org/10.9725/kts.2020.36.3.153"]
["36권3호\npp.161-167","가짜휘발유 판정을 위한 성분 분석\n(Analysis of Component for Determining Illegal Gasoline)","Others","Petroleum is the most used energy source in Korea with a usage rate of 39.5% among the available 1st energy source. The price of liquid petroleum products in Korea includes a lot of tax such as transportation·environment·energy tax. Thus, illegal production and distribution of liquid petroleum is widespread because of its huge price difference, including its tax-free nature, from that of the normal product. Generally, illegal petroleum product is produced by illegally mixing liquid petroleum with other similar petroleum alternatives. In such case, it is easy to distinguish whether the product is illegal by analyzing its physical properties and typical components. However, if one the components of original petroleum product is added to illegal petroleum, distinguishing between the two petroleum products will be difficult. In this research, we inspect illegally produced gasoline, which is mixed with methyl tertiary butyl ether (MTBE) as an octane booster. This illegal gasoline shows a high octane number and oxygen content. Further, we analyze the different types of green dyes used in illegal gasoline through high performance liquid chromatography (HPLC). We conduct component analyses on the simulated sample obtained from premium gasoline and MTBE. Finally, the illegal gasoline is defined as premium gasoline with 10% MTBE. The findings of this study suggest that illegal petroleum can be identified through an analytic method of components and simulated samples.","illegal gasoline(가짜휘발유), GG-MS(가스크로마토그래피-질량분석기), MTBE(엠티비이), dye(염료), simulated test(조제시험)","임영관1†ㆍ원기요2ㆍ강병석3ㆍ박소휘4ㆍ정성5ㆍ고영훈6ㆍ김성수7ㆍ정길형8\n1한국석유관리원 수도권북부본부 팀장, 2한국석유관리원 수도권북부본부 과장, 3한국석유관리원 수도권북부본부 대리, 4한국석유관리원 수도권북부본부 사원, 5한국석유관리원 시험처 과장, 6한국석유관리원 시험처 사원, 7한국석유관리원 시험처 팀장, 8한국석유관리원 수도권북부본부 본부장","https://doi.org/10.9725/kts.2020.36.3.161"]
["36권3호\npp.168-192","엔진 파이어링동안 일정 축 각속도에서 비고정식 피스톤-핀과 연결봉-소단부 부싱 및 피스톤-핀 보스의 접촉면 마모해석\n(Wear Analysis at the Interface of Connecting-Rod Small-End Bushing and Piston-Pin Boss with a Floating Piston-Pinat Constant Angular Velocity during Engine Firing)","Automotive Tribology, Modeling & Simulation in Tribology, Wear Phenomena & Mechanisms","In recently designed diesel engines, the running conditions for piston-pin bearings have become severe because of the higher combustion pressure and increased temperature. Moreover, the metal removal from the bushing material has strongly reduced the ability of the antifriction material to accept asperity contacts. Therefore, it is necessary to find ways of reducing wear scar on the connecting-rod small-end bushing and piston-pin boss bearing related to the higher combustion pressure on the power cell of an engine. In this work, the position and level of material removal from the surfaces of the bushing and bearing under such severe operating conditions - for example, maximum power and torque conditions of a passenger car diesel engine - are estimated for several combinations of surface roughness. First, piston-pin rotating motion is investigated by calculating the friction coefficient at piston-pin bearings, the oil film thickness, and the frictional torques induced by hydrodynamic shear stress. Subsequently, the wear scarring on the surfaces of a connecting-rod small-end bushing and two piston-pin boss bearings related to piston-pin rotational motion is numerically calculated under the maximum power and torque operating conditions. This work is helpful to determine the reasonable surface roughness of the bushing and bearing for reducing wear volume occurring at the interface between a bearing and a shaft.","most oil film thickness scarring wear(마모유발최대유막두께), piston-pin of full floating type(비고정식 피스톤-핀), rotating motion of piston-pin(피스톤-핀의 회전운동), piston-pin boss bearing(피스톤-핀 보스 베어링), connecting-rod small-end bushing(연결봉 소단부 부싱), engine firing condition of constant rpm (일정 엔진회전속도에서의 엔진파이어링조건)","전상명†\n호서대학교 공과대학 기계공학부 자동차공학전공 교수","https://doi.org/10.9725/kts.2020.36.3.168"]
["36권4호\npp.193-198","미세 그루브가 있는 무한폭 Slider 베어링의 윤활해석: 제3보 - 그루브 형상의 영향\n(Lubrication Analysis of Infinite Width Slider Bearing with a Micro-Groove: Part 3 - Effect of Groove Shape)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","Fluid film bearings are among the best devices used for overcoming friction and reducing wear. Surface texturing is a new surface treatment technique used for processing grooves and dimples on the lubricated surface, and it helps to minimize friction further and improve the wear resistance. In several studies, parallel surfaces, such as thrust bearings and mechanical face seals, have been investigated, but most sliding bearings have a convergent film shape. This paper presents the third part of a recent study and focuses on the effect of the groove shape on the lubrication performance of inclined slider bearings, following the two previous papers on the effects of the groove position and depth. We adopted the continuity and Navier – Stokes equations to conduct numerical analyses using FLUENT, which is a commercial computational fluid dynamics code. The groove shape adopted in the numerical analysis is rectangular and triangular, and its depth is varied. The results show that the streamlines, pressure distributions, and groove shape significantly influence the lubrication performance of the inclined slider bearing. For both shapes, the load-carrying capacity (LCC) is maximum near the groove depth, where vortices occur. In the shallow grooves, the LCC of the rectangular shape is higher, but in deeper grooves, that of the triangular shape is higher. The deeper the rectangular groove, the higher the decrease in the frictional force. The results of this study can be used as design data for various sliding bearings.","slider bearing(슬라이더 베어링), surface texturing(표면조직가공), hydrodynamic lubrication(유체 윤활), computational fluid dynamics(CFD, 전산유체역학), numerical analysis(수치해석)","박태조1†ㆍ장인규2\n1경상대학교 기계공학부 교수 · 공학연구원\n2경상대학교 대학원 기계항공공학부 석사과정","https://doi.org/10.9725/kts.2020.36.4.193"]
["36권4호\npp.199-206","CoCr 기반 합금의 초기 마모 특성에 대한 정량적 평가\n(Quantitative Assessment of Initial Wear Characteristics of CoCr-Based Alloys)"," Wear Phenomena & Mechanisms","CoCr-based alloys have been developed as wear-resistant materials owing to their excellent mechanical properties and strong wear resistance. The purpose of this study is to experimentally assess the frictional and wear characteristics of CoCr-based alloys slid against two different counter materials subjected to various normal forces to determine the expansion applicability of CoCr-based alloys. CoCrMo and CoCr alloys were selected as the target materials and NiCr and NiCrB alloys as counter materials. Experimental tests were performed using a pin-on-reciprocating plate tribo-tester under dry lubrication. Before performing the tests, the surface of the specimens was observed through confocal microscopy and the hardness was measured using a micro-Vickers hardness tester. The wear volume of the plate was calculated at the end of the tests using confocal microscope data, and the wear rate was quantitatively obtained based on Archard's wear law. From the results, the wear rates of the CoCrMo specimens that slid against NiCr and NiCrB are 7.69 × 10-6 mm3/Nm and 5.26 × 10-6 mm3/Nm, respectively. The wear rates of the CoCr specimens that slid against NiCr and NiCrB were higher than those of\nthe CoCrMo specimens by factors of approximately 4 and 8, respectively. The CoCrMo specimens further exhibited lower friction characteristics than the CoCr specimens. The findings of this study will be useful for expanded applications of CoCr-based alloys as wear-resistant materials for various mechanical parts.","CoCr-based alloy(CoCr 기반 합금), friction(마찰), wear rate(마모율)","차수빈1*ㆍ김회진1*ㆍ후인 옥-팟2ㆍ정구현3†\n1울산대학교 기계공학부 학사과정생\n2울산대학교 대학원 기계공학과 박사과정생\n3울산대학교 기계공학부 교수","https://doi.org/10.9725/kts.2020.36.4.199"]
["36권4호\npp.207-214","로우스틸 마찰재의 마찰 및 마모특성에 미치는 구리계 재료의 영향\n(Effects of Copper and Copper-Alloy on Friction and Wear Characteristics of Low-Steel Friction Material)"," Automotive Tribology","In this study, we investigated the effects of copper and copper-alloy on the frictional and wear properties of low-steel friction material. The proportions of copper and copper-alloy in the brake friction materials used in passenger cars are very high (approximately 5-20% weight), and these materials have significant effects on friction and wear characteristics. In this study, the effects of cupric ingredients, such as the copper fiber and brass fiber, are investigated using the friction materials based on commercial formulations. After the copper and brass fibers from the same formulation were removed, the frictional and wear characteristics were evaluated to determine the influence of the copper and copper-alloy. We evaluated the frictional and wear characteristics by simulating various braking conditions using a 1/5 scale dynamometer. The results show that the friction material containing copper and brass fibers have excellent frictional stability and a low wear rate compared to the friction material that does not contain copper and brass fibers. These results are attributed to the excellent ductility, moderate melting point, high strength, and excellent thermal conductivity of copper and copper-alloy. We analyzed the surfaces of the friction materials before and after the performing the friction tests using a scanning electron microscope-energy dispersive X-ray spectroscope, confocal microscope, and roughness tester to verify the frictional behavior of copper and copper-alloy. In future studies, it will be applied to the development of copper-free friction materials based on the results of this study.","1/5 scale dynamometer(1/5 스케일 다이나모미터), copper-free(무동), friction material(마찰재), friction test(마찰시험), low-steel friction material(로우스틸 마찰재), transfer film(이착막)","정광기1,3ㆍ이상우2†ㆍ권성욱3ㆍ최성우3ㆍ이희옥3\n1금오공과대학교 대학원 신소재공학과 박사과정\n2금오공과대학교 신소재공학부 정교수\n3상신브레이크 기술연구소 연구원","https://doi.org/10.9725/kts.2020.36.4.207"]
["36권4호\npp.215-231","터보기계에 적용되는 유체 윤활 베어링 및 댐퍼의 최신 연구 동향\n(Recent Advances in Fluid Film Bearings and Dampers for Turbomachinery)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","The paper presents extensive survey and review of experimental and analytical researches on fluid film bearings and squeeze film dampers (SFDs) for turbomachinery available in open literature (major archival international journals) published recently (2018 and 2019 only). Over 60 published research works are reviewed based on the research topics and objectives, the types of bearings, size of bearings, and main design parameters with a brief summary of experiments and/or predictions in each work. Some important findings and general observations about the experimental and/or predictive data are also presented. There are several major trends observed throughout\nthe survey. A large portion of the papers focuses on bearing surface textures and effect of operating and assembly conditions on static and/or dynamic forced performances, as well as bearing surface roughness and wear patterns. Researches on geometry of orifices and recesses in hydrostatic (or hybrid) bearings, as well as bearing system stability predictions using thermohydrodynamic analysis and computational fluid dynamics (CFD), are considered as significant topics. Studies on SFDs mainly focus on experimental identification of force coefficients for various SFD geometries and sealing conditions. Reliable experiments of fluid film bearings and SFDs along with the development of experimentally benchmarked predictive tools enable reinforcement of the path for reliable implementations of the bearing components into high performance rotating machinery operating at extreme and harsh conditions. The extensive list of sources of recent experiments in the available open literature is a welcome addition to the analytical community to gauge the accuracy of predictive tools.","fluid film bearings(유체 윤활 베어링), squeeze film dampers(스퀴즈 필름 댐퍼)","이호원1ㆍ정현성1ㆍ김규만1ㆍ이찬우1ㆍ임호민1ㆍ신세기2ㆍ최승호2ㆍ류 근3†\n1한양대학교 대학원 기계설계공학과 박사과정생\n2한양대학교 대학원 기계설계공학과 석사과정생\n3한양대학교 기계공학과 부교수","https://doi.org/10.9725/kts.2020.36.4.215"]
["36권4호\npp.232-243","수치적 방법을 이용한 3차원 거친 표면의 마모 해석\n(Numerical Wear Analysis of a Three-dimensional Rough Surface)","Wear Phenomena & Mechanisms, Contact Mechanics & Friction","It is essential to predict the amount of wear and surface parameters for a surface where relative motion occurs. In the asperity-based model for wear prediction, only the average contact pressure can be obtained. Hence, the accuracy of wear analysis is poor. In this study, DC-FFT is used to obtain the pressure of each node, and wear analysis is performed by considering the effect of the pressure gradient. The numerical surface generation method is used to create Gaussian, negatively skewed, and positively skewed surfaces for wear analysis. The spatial and height distributions of each surface are analyzed to confirm the effectiveness of the generated surface. Furthermore, wear analysis is performed using DC-FFT and Archard's wear formula. After analysis, it is confirmed that all peaks are removed and only valleys remain on the surface. The RMS roughness and Sk continue to decrease and Ku increases as the cycle progresses. It is observed that the surface parameters are significantly affected by the radius of curvature of the asperity. This analysis method is more accurate than the existing average wear and truncation models because the change in asperity shape during the wear process is reflected in detail.","DC-FFT method(DC-FFT 방법), numerical analysis(수치해석), rough surface(거친 표면), running-in(길들임), sliding wear(미끄럼 마모)","김윤지1ㆍ서준호2ㆍ김봉준1ㆍ유용훈3†\n1부산대학교 기계공학부 석사과정생, 2부산대학교 기계공학부 조교수, 3부산대학교 기계공학부 박사후연구원","https://doi.org/10.9725/kts.2020.36.4.232"]
["36권4호\npp.244-252","분말 야금에 의해 소결된 강철의 트라이볼로지 특성 향상\n(Improvement in Tribological Properties of Carbon Steel Sintered by Powder Metallurgy)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","Materials manufactured by powder metallurgy (PM) are widely used in various applications such as water pump, shock absorber, and airplane components due to the reduction in the cost and weight. In this study, tribological properties of carbon steel subjected by surface treatment were investigated. The main purpose is to increase the strength and improve the tribological properties by reducing pores that formed by PM. Moreover, the surface treatment was carried out at room and high temperatures (RT and HT). The surface roughness of the untreated (NON) and treated (AFTER) samples was measured. It was found that the surface roughness was reduced after both the RT AFTER and HT AFTER compared to RT NON sample. The tribological properties of the samples were performed against bearing steel ball under dry conditions. The friction coefficient of the RT NON samples was reduced by 22% and 56% RT AFTER and HT AFTER, respectively. The wear volume of the RT NON sample was also reduced by 43% and 87% RT AFTER and HT AFTER, respectively. Tribocorrosion tests were also performed and it was found that the surface of the RT AFTER, HT AFTER samples was less corroded compared to RT NON sample. The HT AFTER sample demonstrated a relatively higher corrosion potential in comparison with the RT AFTER samples. Hence, it was confirmed that after surface modification the surface roughness and hardness of the samples were significantly improved resulting in improvement in tribological and tribocorrosion behaviors of PM carbon steel.","powder metallurgy(분말야금), surface treatment(표면처리), wear(마모), tribocorrosion(마찰부식)","최세이미1ㆍ카림바예프 루슬란2ㆍ편영식3ㆍ아마노프 아웨즈한4†\n1선문대학교 대학원 융합과학기술학과 석사과정생, 2선문대학교 대학원 융합과학기술학과 박사과정생, 3선문대학교 융합과학기술학과 연구교수, 4선문대학교 기계공학과/융합과학기술학과 부교수","https://doi.org/10.9725/kts.2020.36.4.244"]
["36권5호\npp.253-261","수정된 후방 플로팅 링 실을 적용한 7톤급 터보펌프 산화제 펌프의 진동 및 압력 측정\n(Measurements of Vibration and Pressure of an Oxidizer Pump fora 7-tonf Turbopump with a Modified Rear Floating Ring Seal)","Space/Extreme Tribology","In this paper, we present an experimental investigation of the frequency characteristics and a visual inspection of an oxidizer pump with a modified rear-floating ring seal for a 7-tonf turbopump. An oxidizer pump typically operates at high rotational speeds and under cryogenic conditions. Despite its low hydraulic efficiency, the floating ring seal is frequently employed as a leakage control solution for turbomachinery because it effectively reduces abrasion by friction. When the oxidizer pump starts up, the floating ring moves excursively but locks up stably against the pump casing when the contact pressure increases. The compressive force on the floating ring depends on the hydrodynamic forces induced by the flow through the floating ring. This force is controlled by the nose position of the floating ring. Based on a validation test for a 7-tonf turbopump with two types of floating rings, we concluded that the floating ring with a small diameter nose can move easily with a low contact pressure in the cooling path. This leads to instability of the pressure fluctuation around the floating ring. In contrast, a floating ring with a large diameter nose has a high contact pressure and attaches strongly to the casing, which causes wear and frictional oxidation between the contact surfaces of the impeller and the floating ring.","floating ring seal(플로팅 링 실), turbopump(터보펌프), oxidizer pump(산화제 펌프), high frequency signal(고주파 신호), pressure fluctuation(압력 섭동), static pressure(정압)","배준환1,2ㆍ곽현덕3ㆍ최창호3ㆍ최종수4†\n1한국항공우주연구원 터보펌프팀 선임연구원, 2충남대학교 항공우주공학과 박사과정생, 3한국항공우주연구원 터보펌프팀 책임연구원, 4충남대학교 항공우주공학과 정교수","https://doi.org/10.9725/kts.2020.36.5.253"]
["36권5호\npp.262-266","마모해석을 위한 고유치해석과 Adaptive Meshing 알고리듬을 이용한 수치해석 비교\n(A Comparative Study on Eigen-Wear Analysis and Numerical Analysis using Algorithm for Adaptive Meshing)","Contact Mechanics & Friction ","Herein, we present a numerical investigation of wear analysis of sliding systems with a constant speed subjected to Archard’s wear law. For this investigation, we compared two methods: eigen-wear analysis and adaptive meshing technique. The eigen-wear analysis is advantageous to predict the evolution of contact pressure due to wear using the initial contact pressure and contact stiffness. The adaptive meshing technique in finite element analysis is employed to obtain transient wear behavior, which needs significant computational resources. From the eigen-wear analysis, we can determine the appropriate element size required for finite element analysis and the time increment required for wear evolution by a dimensionless variable above a certain value. Since the prediction of wear depends on the maximum contact pressure, the finite element model should have a reasonable representation of the maximum contact pressure. The maximum contact pressure and wear amount according to this dimensionless variable shows that the number of fine meshes in the contact area contributes more to the accuracy of the wear analysis, and the time increment is less sensitive when the number of contact nodes is significantly larger. The results derived from a two-dimensional wear model can be applied to a three-dimensional wear model.","adaptive-lagrange euler meshing(적응적 라그랑쥐 오일러 메쉬), archard wear model(아차드 마모모델), eigenanalysis(고유치 해석), finite element analysis(유한요소해석), wear analysis(마모해석)","장일광1·장용훈2†\n1연세대학교 기계공학과 연구교수, 2연세대학교 기계공학과 교수","https://doi.org/10.9725/kts.2020.36.5.262"]
["36권5호\npp.267-273","광경화성 레진의 성분 변화에 대한 소수성 표면 제작을위한 공정 조건\n(Process Conditions for the Fabrication of Hydrophobic Surfaces with Different Photo-curable Resins)","Bio-Tribology/Biomimetics","This study experimentally investigates hydrophobic surfaces fabricated via additive manufacturing. Additive manufacturing, commonly known as 3D printing, is the process of joining materials to fabricate parts from 3D model data, usually in a layer-upon-layer manner. Digital light processing is used to fabricate hydrophobic surfaces in this study. This method uses photo-curable resins and ultraviolet (UV) sources. Moreover, this technique generally has faster shaping speeds and is advantageous for the fabrication of small components because it enables the fabrication of one layer at a time. Two photo-curable resins with different compositions are used to fabricate micro-patterns of hydrophobic surfaces. The resins are composed of a photo-initiator, monomer, and oligomer. Experiments are conducted to determine suitable process conditions for the fabrication of hydrophobic surfaces depending on the type of resin. The most important factors affecting the process conditions are the UV exposure time and slice thickness. The fabrication capability according to the process conditions is evaluated using the side and top views of the micro-patterns observed using a microscope. The micro-patterns are collapsed and intertwined when the exposure time is short because sufficient light (heat) is not applied to cure the photo-curable resin with a given slice thickness. On the other hand, the micro-patterns are attached to each other when the exposure time is prolonged because the over-curing time can cure the periphery of a given shape. When the slice is thicker, the additional curing area is enlarged in each slice owing to the straightness of UV light, and the slice surface becomes rough.","additive manufacturing(적층 제조), contact angle(접촉각), hydrophobic surface(소수성 표면), photocurable resin(광경화성 레진)","홍성호1†·우흥식2\n1동국대학교 창의융합공학부 기계시스템공학전공 조교수, 2동국대학교 창의융합공학부 안전공학전공 교수","https://doi.org/10.9725/kts.2020.36.5.267"]
["36권5호\npp.274-278","자기유변탄성체를 이용한 스퀼 소음 저감 타당성 연구\n(Feasibility Study of Squeal Noise Reduction using Magneto-rheological Elastomer)","Tribology in Design & Manufacturing (Metalworking / Machining) ","This study investigates the possibility of reducing squeal noise generated at the contact point between an elastomer and glass by using the properties of a magneto-rheological elastomer (MRE) whose stiffness changes with the application of a magnetic field. Previously, squeal noise was mainly observed in the unstable section caused by the weakening of friction due to velocity. Previous studies have shown that squeal noise decreases as the stiffness increases. Accordingly, this study is conducted to control the unstable area of the friction curve and to reduce the noise by inducing the stiffness change of the MRE by applying a magnetic field. The friction, vibration, and noise characteristics are measured using a reciprocating friction tester. The frequency ranges of vibration and noise measured with the accelerometer and sound sensor show similar results. When a magnetic field is applied to the MRE, there is significantly lower noise compared with the case without the application of the magnetic field. The average coefficient of friction decreases with the application of the magnetic field. The maximum coefficient of friction increases rapidly at the turning point and decreases when the magnetic field is applied. This shows that the mechanical properties of the MRE change due to the magnetic field, and the noise and friction coefficient also decrease.","friction(마찰), magnetic field(자기장), magneto-rheological elastomer(자기유변탄성체), squeal noise(스퀼 소음), vibration(진동)","송혁근1·이철희2†\n1인하대학교 대학원 건설기계공학과 석사과정생, 2인하대학교 기계공학과 교수","https://doi.org/10.9725/kts.2020.36.5.274"]
["36권5호\npp.279-289","MW급 대용량 유도전동기 축계의 모드실험 기반 회전체동역학 해석모델 수립 및 위험속도 예측\n(Rotordynamic Model Development and Critical Speed Estimation Through Modal Testing for the Rotor-Bearing Systemof a MW Class Large-Capacity Induction Motor)","Others ","In this paper, a method is proposed for establishing an approximate prediction model of rotordynamics through modal testing. In particular, the proposed method is applicable to systems that cannot be established according to conventional methods owing to the absence of information regarding the dimensions and material of the rotor–bearing system. The proposed method is demonstrated by employing a motor dynamometer driven by a 1 MW class induction motor without dimension and material information. The proposed method comprises a total of seven steps, wherein an initial model is established by incorporating approximate dimensions and material information, and the model is improved on the basis of the natural frequency characteristics of the system. During model improvement, the modification factor is introduced for adjusting the elastic modulus and shear modulus of the system. Analysis of critical speed and imbalance response indicates that the separation margin is 67% and the maximum vibration amplitude is less than the amplitude limit of 0.032 mm under the API 611 standard, which means that the motor dynamometer can stably operate at a rated speed of 1800 rpm. Hence, the obtained results validate the feasibility of the proposed method. Furthermore, for broad usage, it is necessary to accordingly apply and validate the proposed method for various rotor–bearing systems.","large-capacity induction motor(대용량 유도전동기), rotordynamics(회전체동역학), critical speed(위험속도)","박지수1·최재학2·김동준2·심규호3†\n1서울과학기술대학교 기계시스템디자인공학과 연구원, 2한국전기연구원 전기응용연구본부 연구원, 3서울과학기술대학교 기계시스템디자인공학과 부교수","https://doi.org/10.9725/kts.2020.36.5.279"]
["36권5호\npp.290-296","Molecular Dynamic Simulation for Penetrationof Carbon Nanotubes into an Array of Carbon Nnantotubes","Contact Mechanics & Friction ","When two layers of carbon nanotube (CNT) arrays are loaded to mate, the free ends of individual CNTs come into contact at the interface of the two layers. This leads to a higher contact resistance due to a smaller contact region. However, when the free CNT ends of one array penetrate into the mating array, the contact region increases, effectively lowering the contact resistance. To explore the penetration of mating CNTs, we perform molecular dynamic simulations of a simple unit cell model, incorporating four CNTs in the lower array layer coupled with a single moving CNT on the upper layer. The interaction with neighboring CNTs is modelled by long-range carbon bond order potential (LCBOP I). The model structure is optimized by energy minimization through the conjugate gradient method. A NVT ensemble is used for maintain a room temperature during simulation. The time integration is performed through the velocity-Verlet algorithm. A significant vibrational motion of CNTs is captured when penetration is not available, resulting in a specific vibration mode with a high frequency. Due to this vibrational behavior, the random behaviors of CNT motion for predicting the penetration are confirmed under the specific gap distances between CNTs. Thus, the probability of penetration is examined according to the gap distance between CNTs in the lower array and the aspect ratio of CNTs. The penetration is significantly affected by the vibration mode due to the van der Waals forces between CNTs.","carbon nanotube array, inter-nanotube interfaces, penetration, molecular dynamic simulation, vibration","Ilkwang Jang1 and Yong Hoon Jang2†\n1Research Professor, School of Mechanical Engineering, Yonsei University, 2Professor, School of Mechanical Engineering, Yonsei University","https://doi.org/10.9725/kts.2020.36.5.290"]
["36권6호\npp.297-306","윤활유 분석 센서를 통한 기계상태진단의 문헌적 고찰 (윤활유 센서의 종류와 기능)\n(Literature Review of Machine Condition Monitoring with Oil Sensors-Types of Sensors and Their Functions)","Condition Monitoring & Maintenance System (System Reliability)","This paper reviews studies on the types and functions of oil sensors used for machine condition monitoring. Machine condition monitoring is essential for maintaining the reliability of machines and can help avoid catastrophic failures while ensuring the safety and longevity of operation. Machine condition monitoring involves several components, such as compliance monitoring, structural monitoring, thermography, non-destructive testing, and noise and vibration monitoring. Real-time monitoring with oil analysis is also utilized in various industries, such as manufacturing, aerospace, and power plants. The three main methods of oil analysis are off-line, in-line, and on-line techniques. The on-line method is the most popular among these three because it reduces human error during oil sampling, prevents incipient machine failure, reduces the total maintenance cost, and does not need complicated setup or skilled analysts. This method has two advantages over the other two monitoring methods. First, fault conditions can be noticed at the early stages via detection of wear particles using wear particle sensors; therefore, it provides early warning in the failure process. Second, it is convenient and effective for diagnosing data regardless of the measurement time. Real-time condition monitoring with oil analysis uses various oil sensors to diagnose the machine and oil statuses; further, integrated oil sensors can be used to measure several properties simultaneously.","function(기능), machine condition monitoring(기계상태진단), oil sensor(오일 센서)","홍성호†\n동국대학교 창의융합공학부 기계시스템공학전공 조교수","https://doi.org/10.9725/kts.2020.36.6.297"]
["36권6호\npp.307-314","윤활유 분석 센서를 통한 기계상태진단의 문헌적 고찰(적용사례)\n(Review of Application Cases of Machine Condition Monitoring Using Oil Sensors)","Condition Monitoring & Maintenance System (System Reliability)","In this paper, studies on application cases of machine condition monitoring using oil sensors are reviewed. Owing to rapid industrial advancements, maintenance strategies play a crucial role in reducing the cost of downtime and improving system reliability. Consequently, machine condition monitoring plays an important role in maintaining operation stability and extending the period of usage for various machines. Machine condition monitoring through oil analysis is an effective method for assessing a machine's condition and providing early warnings regarding a machine's breakdown or failure. Among the three prevalent methods, the online analysis method is predominantly employed because this method incorporates oil sensors in real-time and has several advantages (such as prevention of human errors). Wear debris sensors are widely employed for implementing machine condition monitoring through oil sensors. Furthermore, various types of oil sensors are used in different machines and systems. Integrated oil sensors that can measure various oil attributes by incorporating a single sensor are becoming popular. By monitoring wear debris, machine condition monitoring using oil sensors is implemented for engines, automotive transmission, tanks, armored vehicles, and construction equipment. Additionally, such monitoring systems are incorporated in aircrafts such as passenger airplanes, fighter airplanes, and helicopters. Such monitoring systems are also employed in chemical plants and power plants for managing overall safety. Furthermore, widespread application of oil condition diagnosis requires the development of diagnostic programs.","application case(적용 사례), machine condition monitoring(기계상태진단), oil sensor(오일 센서)","홍성호†\n동국대학교 창의융합공학부 기계시스템공학전공 조교수","https://doi.org/10.9725/kts.2020.36.6.307"]
["36권6호\npp.315-319","탄소나노튜브 코팅의 마찰/마모 특성에 대한 나노메쉬 구조의 영향\n(Effect of Nanomesh Structure Variation on the Friction andWear Characteristics of Carbon Nanotube Coatings)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ,Micro/Nano-Tribology","In various fields, several studies based on carbon nanotubes (CNTs) have been conducted. The results of previous studies, wherein CNT coatings have been incorporated as solid lubricants, demonstrate that the friction and wear characteristics of CNT coatings can be improved through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure comprising CNT strands. In this study, the friction and wear characteristics of the following are compared: CNT coating formed by spin coating of CNT solution, compressed CNT coating, and compressed/heated CNT coating (wherein CNT strands are squeezed through compression and/or heating). It is observed that the friction coefficient of the CNT coating having the largest number of voids between the CNT strands is significantly lower than those of the compressed CNT coating and the compressed/heated CNT coating. The wear tracks of the compressed CNT coating and the compressed/heated CNT coating indicate that some parts become torn or adhere into a lump. However, in the case of the CNT coating, a smooth wear surface is formed by rubbing. Furthermore, as the void space between the squeezed and adhered CNT strands decreases, the resistance to structural deformation increases, thereby resulting in an increased frictional force and a wear pattern that becomes torn or forms a lump. Hence, the results obtained from this study corroborate that the friction and wear characteristics of CNT coatings can be enhanced through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure of CNT coatings.","carbon nanotube coating(탄소나노튜브 코팅), friction(마찰), nanomesh structure(나노메쉬 구조), stiffness control(강성 조절), wear(마모)","김해진1·김창래2†\n1경상대학교 기계항공공학부 조교수, 2조선대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2020.36.6.315"]
["36권6호\npp.320-323","Modification of Thin Film Friction and Wear Models with Effective Hardness","Micro/Nano-Tribology ","Thin film coatings are commonly exploited to minimize wear and optimize the frictional behavior of various precision mechanical systems. The enhancement of thin film durability is directly related to the performance maximization of the system. Therefore, a fine approach to analyze the thin film wear behavior is required. Archard’s equation is a representative and well-developed law that defines the wear coefficient, which is the probability of creating wear particles. A ploughing model is a commonly used model to determine the friction force during the abrasive contact. The equations demonstrate that the friction force and wear coefficient are inversely proportional to the hardness of the material. In this study, Archard’s equation and ploughing models are modified with an effective hardness to minimize the gap between the experimental and numerical results. It is noted that the effective hardness is the hardness variation with respect to the penetration depth owing to the substrate effect. The nanoindentation method is utilized to characterize the effective hardness of Cu film. The wear coefficient value considering the effective hardness is more than three times higher than that without considering the effective hardness. The friction force predicted with the effective hardness agreed better with the results obtained directly from the friction force detecting sensor. This outcome is expected to improve the accuracy of friction and wear amount predictions.","archard’s wear model, ploughing friction model, elastic modulus, hardness, nanoindentation","Chang-Lae Kim1 and Hae-Jin Kim2†\n1Assistant Professor, Dept. of Mechanical Engineering, Chosun University, 2Assistant Professor, Dept. of Mechanical and Aerospace Engineering, Gyeongsang National University","https://doi.org/10.9725/kts.2020.36.6.320"]
["36권6호\npp.324-331","분리 상태를 고려한 탄성마찰시스템의 임계 쐐기 계수\n(Critical Wedging Coefficient in Frictional ElasticSystem Considering Separation State)","Contact Mechanics & Friction ","Wedging in a frictional elastic system is defined if the state of stick exists after the external loading on the system is removed. This paper presents a method to determine the critical coefficient of wedging for an elastic frictional system by considering the separation state. Wedging is always possible if the coefficient of friction exceeds a critical value known as the critical wedging coefficient. This method requires two concepts: a necessary and sufficient condition for wedging, which can be interpreted as positive spanning sets of constraint vectors existing in the wedged system, and the minimal positive basis that enables a minimum wedging coefficient. The algorithm based on the positive spanning concept is repeatedly executed after eliminating nodes from the contact stiffness matrix, for which the separation states are impending. The simulation results show that once a node enters the separation state, it never returns to the contact state again and the critical wedging coefficient reduces during repeated algorithm execution. The benefit of this method is that the computation time permits handling models with large numbers of contact nodes. The algorithm can also numerically find the critical wedging coefficient, thereby contributing to fastening and assembly performance improvements in mechanical systems.","wedging(쐐기현상), critical wedging coefficient(임계쐐기마찰계수), positive spanning(양의 생성), discrete frictional system(이산마찰 시스템), separation state(분리상태)","김상규1·장용훈2†\n1연세대학교 대학원 기계공학과 석사과정생, 2연세대학교 기계공학과 교수","https://doi.org/10.9725/kts.2020.36.6.324"]
["36권6호\npp.332-341","범프 타입 포일 스러스트 베어링의 정하중 구조 강성 및 손실 계수 차이에 관한 실험적 연구\n(On the Bearing-to-Bearing Variability in ExperimentallyIdentified Structural Stiffnesses and Loss Factors of Bump-TypeFoil Thrust Bearings under Static Loads)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","High-speed turbomachinery implements gas foil bearings (GFBs) due to their distinctive advantages, such as high efficiency, lesser part count, and lower weight. This paper provides the test results of the static structural stiffnesses and loss factors of bump-type foil thrust bearings with increasing preload and bearing deflection. The focus of the current work is to experimentally quantify variability in structural stiffnesses and loss factors among the four test thrust bearings with identical design values and material of the bump and top foil geometries using the same (open-source) fabrication method. A simple test setup, using a rigidly mounted non-rotating shaft and thrust disk, measures the bearing bump deflections with increasing static loads on the test bearing. The inner and outer diameters of the test bearings are 41 mm and 81 mm, respectively. The loss factor, best-representing energy dissipation in the test bearings, is estimated from the area inside the local hysteresis loop of the load versus the bearing deflection curve. The measurements show that structural stiffnesses and loss factors of the test bearings significantly rely on applied preloads and bearing deflections. Local structural stiffnesses of the test bearings increase with applied preloads but decrease with bearing deflections. Changes of loss factors are less sensitive to applied preloads and bearing deflections compared to those of structural stiffnesses. Up to 35% variability in static load structural stiffnesses is found between bearings, while up to 30% variability in loss factors is found between bearings.","foil bearings(포일 베어링), thrust bearings(스러스트 베어링), structural stiffness(구조 강성), loss factor (손실 계수), experimental parameter identification(실험적 계수 규명)","이성진1†·류근2‡·정진희3·류솔지4\n1한양대학교 대학원 기계설계공학과 박사수료생, 2한양대학교 기계공학과 부교수, 3LG전자 H&A사업본부 H&A연구센터 에어솔루션연구소 자문역, 4LG전자 H&A사업본부 H&A연구센터 에어솔루션연구소 산업용에어솔루션선행연구팀 선임연구원","https://doi.org/10.9725/kts.2020.36.6.332"]
["36권6호\npp.342-349","식물성 오일의 혼합조건에 따른 윤활 특성 연구\n(Study on Lubrication Characteristics of Vegetable Oil Basedon Blending Condition)","Lubrication (Lubricants & Additives) ","The rapidly increasing threats to the environmental has increased the demand for biodegradable lubricants. Vegetable oils, such as olive, coconut, and sunflower oils, are readily obtainable and are not harmful, unlike synthetic and mineral oils. The tribological characteristics of these oils should be adequately examined for industrial applications. In this study, the lubrication characteristics of olive oil is investigated using a pin-on-disk-type tribometer under 500 gf of normal force, and the examination results are compared and analyzed with those of commercial synthetic lubricants for friction and wear. In addition, stearic acid, which is a type of saturated fatty acid, is mixed with olive oil as an additive to improve its lubrication characteristics. Olive oil with stearic acid additive is thus observed to exhibit the lowest friction coefficient for rotational speeds of 200 to 800 rpm. According to the wear analysis, a minimal amount of wear is observed when no additive is used. Hence, olive oil is able to effectively reduce friction and wear at relatively low speeds. These low friction and wear characteristics of olive oil are attributed to its compatibility with the substrate.","olive oil(올리브유), fatty acid(지방산), lubrication(윤활), additives(첨가제), wear(마모)","정희영1·김현준2,3†\n1경북대학교 정밀기계공학과 학부과정생, 2경북대학교 정밀기계공학과 부교수, 3경북대학교 미래과학기술융합학과 부교수","https://doi.org/10.9725/kts.2020.36.6.342"]
["36권6호\npp.350-358","마찰 방법에 따른 핫스탬핑 마모 거동의 연구 동향\n(Review on the Wear behavior of the Hot Stamping Processwith Respect to Friction Testing Methods)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials) ","Hot stamping is an effective and suitable process widely used in automotive applications, though critical issues such as the transfer of the coating materials and build-up of these materials on tool surfaces have been encountered. Past researches figured out the resultant wear phenomenon using pin-on-disc and drawing (for example, strip drawing and deep drawing) methods to mimic the process and analyzed the wear behavior with respect to the influencing factors such as surface coating, load, and roughness. Although the pin-on-disc is a conventional and widely-used method, it presented a methodological limitation when simulating the hot stamping process by forming a new blank each time, and hence, a drawing-based friction method has been proposed and developed. Each drawing method applies loads in a different way, resulting in a different wear behavior. Notably, the deep drawing process is most similar to the hot stamping process compared to other drawing methods. In this paper we present a review of the friction testing methods mimicking the hot stamping process and the associated wear behavior. This can be helpful in presenting a step-by-step approach and different perspectives on the wear behavior in the hot stamping process.","hot stamping(핫스탬핑), wear(마모), high-temperature friction(고온 마찰), surface coating(표면 코팅), intermetallic compounds(금속간화합물)","지민기1·전태성2†\n1인천대학교 기계공학과 석사과정생, 2인천대학교 기계공학과 부교수","https://doi.org/10.9725/kts.2020.36.6.350"]
["36권6호\npp.359-364","그루브의 Trap 효과에 대한 CFD 해석:제2부 - 그루브 모서리의 곡률반경 변화\n(CFD Analysis of Trap Effect of Groove in Lubricating Systems:Part II – Variation in Radius of Curvature of Groove Edge)","Modeling & Simulation in Tribology","Numerical investigation of the groove trap effect with variation in the groove-edge radius of curvature is presented here. The trap effect is evaluated in a two-dimensional sliding bearing using computational fluid dynamics (CFD). This simulation is based on the discrete phase model (DPM) and standard k - ε turbulence model using commercial CFD software, FLUENT. The numerical results are evaluated by comparisons with streamlines and particle trajectories in the grooves. Grooves are applied to various lubrication systems to improve their lubrication characteristics, such as load carrying capacity increment, leakage reduction, frictional loss reduction, and preventing three-body abrasive wear due to trapping effect. This study investigates the grove trapping effect for various groove-edge radius of curvature values and Reynolds numbers. The particle is assumed to be made of steel, with a circular shape, and is injected as a single particle in various positions. One-way coupling is used in the DPM model because the single particle injection condition is applied. Further, the “reflect” condition is applied to the wall boundary and “escape” condition is used for the “pressure inlet” and “pressure outlet” boundaries. From the numerical results, the groove edge radius is found to influence the groove trap effect. Moreover, the groove trap effect is more effective when applying the groove edge radius.","CFD(전산유체역학), edge(모서리), groove(그루브), trap effect(포집 효과)","홍성호†\n동국대학교 창의융합공학부 기계시스템공학전공 조교수","https://doi.org/10.9725/kts.2020.36.6.359"]
["36권6호\npp.365-370","실리콘 오일 점도에 따른 ABS-like 레진의 트라이볼로지 특성\n(Tribological Characteristics of ABS-like Resin Accordingto Silicon Oil Viscosity)","Tribology of Materials (Characterization / Polymer Tribology / NewㆍSmart Materials)","Recently, additive manufacturing (AM) technology has been applied to various industries such as automotive, aviation, medical, and electronics. Most prior studies are limited to the mechanical properties of printed materials, and few studies are being conducted on their tribological characteristics. However, the friction and wear characteristics of the material should be studied in order to utilize the components manufactured using AM technology as mechanical parts. In this study, the friction and wear characteristics of acrylonitrile-butadiene-styrene (ABS)-like resin printed with stereo lithography apparatus (SLA) 3D printing are evaluated according to the viscosity of silicon oil lubricant using a ball-on-disk experiment. Lubricants with a viscosity of 500, 1000, and 2000 cSt are prepared for the experiment. If silicon oil lubricants are used during the ball-on-disk test, the coefficient of friction (COF) and wear rates are significantly reduced, and the higher the viscosity of the lubricant, the lower will be the COF and wear rates. It is also verified that the temperature of the specimen owing to friction also decreases according to the viscosity of the lubricant. This is because of the silicon oil film thickness, and the higher the viscosity of the lubricant, the thicker will be the oil film. More studies on the tribological characteristics of 3D printing materials and suitable lubricants will be required to use 3D printed parts as mechanical elements.","friction(마찰), wear(마모), ABS-like resin(ABS 유사 수지), lubricant(윤활제), viscosity(점도)","박성현1·손준규1·우성웅2·류의진2·이현섭3†\n1동명대학교 대학원 기계시스템공학과 석사과정생, 2동명대학교 기계공학부 학사과정생, 3동명대학교 기계공학부 부교수","https://doi.org/10.9725/kts.2020.36.6.365"]
["36권6호\npp.371-377","볼 베어링의 전동체 기반 및 응력 기반 접촉 피로수명의 비교\n(Comparison of Rolling Element Loads and Stress-basedFatigue Life Predictions for Ball Bearings)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements)","In In this study, we compared the results of a ball bearing life prediction model based on rolling element loads with the results of fatigue life prediction of ball bearings when a stress-based contact fatigue life prediction technique is applied to the ball bearing. We calculate the load acting on each rolling element by the external load of the bearing and apply the result to the Lundberg–Palmgren (LP) theory to calculate ball bearing life based on the rolling element. We also calculate stress-based ball bearing life through contact and fatigue analyses based on contact modeling of the ball and raceway while considering the fatigue test results of AISI 52100 steel. In stress-based life prediction, we use three high-cycle fatigue-determination equations that can predict the fatigue life when multi-axis proportional loads such as rolling-slide contact conditions are applied. These equations are derived from the stress invariant and critical plane methods and the mesoscopic approach. Life expectancy results are compared with those of the LP model. Results of the analysis indicated that the fatigue life was predicted to be lower in the order of the Crossland, Dang Van, and Matake models. Of the three, the Dang Van fatigue model was found to be the closest to the LP life.","ball bearing(볼 베어링), fatigue life(피로 수명), L-P model(L-P모델)","곽재섭1·박영환1·김찬중2·김태완1†\n1부경대학교 기계공학과 교수, 2부경대학교 기계공학과 부교수","https://doi.org/10.9725/kts.2020.36.6.371"]
["36권6호\npp.378-384","유한요소해석에 의한 코팅면의 브리넬 경도 평가: 제1보 - 타당성 연구\n(Evaluation of Brinell Hardness of Coated Surface by FiniteElement Analysis: Part 1 - A Feasibility Study)","Modeling & Simulation in Tribology, Contact Mechanics & Friction","The friction surfaces of mechanical parts are heat-treated or coated with hard materials to minimize wear. Increasing the hardness is a very useful way to reduce abrasive wear. The general Brinell hardness test, which is widely used for metallic materials, is not suitable because it hardly shows any change in hardness when coated with thin films. In this study, we propose a basis for the application of the new Brinell hardness test method to the coated friction surface. An indentation analysis of the rigid sphere and elastic-perfectly plastic materials is performed using a commercial finite element analysis software. The results indicate that their load-to-diameter ratio is the same; the Brinell hardness test method can be applied even when the indenter diameter is on the micrometer scale. In the case of hard coating, it is difficult to calculate Brinell hardness using the diameter of the indentation, but the study revealed, for the first time, that it can be calculated using the depth of the indentation regardless of coating. The change in hardness owing to thin film coating over a wide load range implies that the hardness evaluation method is appropriate. Additional studies on various properties related to the substrate and coating material are required to apply the proposed method.","brinell hardness(브리넬 경도), coating(코팅), indentation analysis(압입해석), finite element analysis(유한요소해석)","박태조1†·강정국2\n1경상대학교 기계공학부 교수 · 공학연구원, 2경상대학교 기계항공정보융합공학부 학부생","https://doi.org/10.9725/kts.2020.36.6.378"]
["36권6호\npp.385-390","수분오염에 따른 경유의 연료적 특성\n(The Fuel Characteristics of Diesel by Water Contamination)","Tribology Applications (Industrial Case Studies)","It rains heavily, such as long rain and typhoons, during a typical rainy season in Korea. In this season, several fuel contamination accidents by water and vehicular problems caused by water contaminated fuel occur. Many research groups have studied the effects of water contaminated fuel on vehicles and environment. However the characteristics of water contaminated fuel have not been studied. In this study, we prepared diesel samples with a constant ratio of water (0~30 volume %) using an emulsifier. Then, we analyzed these diesel samples for their representative fuel properties. In the analytical results, diesel with 30% water showed an increase in fuel properties such as density (823→883 kg/m3), kinematic viscosity (2.601→6.345 mm2/s), flash point (47→56oC), pour point (-22→2oC), CFPP (cold filter plugging point) (-17→20oC) and copper corrosion number (1a→2a). The low temperature characteristics, such as low pour point and CFPP, blocks the fuel filter in the cold season. In addition, water contaminated decreases lubricity (190→410 μm) under high frequency reciprocating rig (HFRR) and derived cetane number (54.81→34.25). The low lubricity of fuel causes vehicle problem such as pump and injector damage owing to severe friction. In addition, the low cetane diesel fuel increases exhaust gases such as NOx and particulate matters (PM) owing to incomplete combustion. This study can be used to identify the problems caused by water contamination to vehicle and fuel facilities.","diesel(경유), water contamination(수분오염), HFRR(경유윤활성시험), corrosion(부식), derived cetane number(유도세탄가)","임영관1†·원기용2·강병석3·박소휘4·박장민5·강대혁6\n1한국석유관리원 수도권북부본부 팀장, 2한국석유관리원 수도권북부본부 과장, 3한국석유관리원 수도권북부본부 대리, 4한국석유관리원 수도권북부본부 사원, 5한국석유관리원 석유기술연구소 대리, 6한국석유관리원 수도권북부본부 본부장","https://doi.org/10.9725/kts.2020.36.6.385"]

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["권호","제목","토픽","초록","키워드","저자","DOI"]
["37권1호\npp.1-10","SLA을 이용한 소수성 표면 제작\n(Fabrication of Hydrophobic Surfaces with Stereolithography)","Bio-Tribology/Biomimetics ","This paper presents the experimental results of hydrophobic surfaces developed using a stereolithography-based additive-manufacturing technique. The additive manufacturing technique can be used to manufacture objects with complex geometries from computer-aided design data. Several additive manufacturing methods, such as selective laser sintering, fused deposition modeling, stereolithography apparatus (SLA), and inkjet-based system, have been developed. The SLA is a form of three-dimensional printing technology used to create prototypes, patterns, and production parts in successive layers through photochemical processes. Light causes chemical monomers and oligomers to cross-link together to form objects composed of polymers. Moreover, this method is economical for fabricating surfaces with high output resolution and quality. Here, we fabricate various surfaces using different shapes using an SLA. The surfaces with micro-patterns are fabricated for 10 cases, including the biomimetic surface. The fabricated surfaces with various micro-patterns are evaluated for hydrophobicity performance based on the static contact angle. The contact angle is measured three times for each case, and the averaged value is used. The results indicate that the arrangements in a staggered structure have a larger contact angle than those in a line when the same micro-pattern is applied. Moreover, the mimetic surfaces exhibit more hydrophobic characteristics than those of artificial micro-patterns. ","additive manufacturing(적층 제조), contact angle(접촉각), hydrophobic surface(소수성 표면)","홍성호†\n동국대학교 창의융합공학부 기계시스템공학전공","https://doi.org/10.9725/kts.2021.37.1.1"]
["37권1호\npp.11-17","온도, 속도, 그리고 하중 변화에 따른 볼 베어링용 그리스의 수명평가\n(Life Evaluation of Grease for Ball Bearings Accordingto Temperature, Speed, and Load Changes)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","Ball bearing is a device that supports and transmits a load acting on a rotating shaft, and it is a type of rolling bearings that uses the rolling friction of the balls by inserting balls between the inner ring and the outer ring. Grease, which is prepared by mixing a thickener with a base oil, is a lubricant commonly used in bearings and has the advantage of a simple structure and easy handling. Bearings are increasingly being used in high value-added products such as semiconductors, aviation, and robots in the era of the 4th industrial revolution. Accordingly, there is an increasing demand for bearing grease. The selection of grease is an important factor in the bearing design. Therefore, a study must be conducted on the grease life evaluation to select an appropriate grease according to operating conditions such as a high temperature, high rotational speed, and high load. In this study, we evaluate the life of ball-bearing grease according to various operating conditions, namely, temperature, speed, and load changes. For this, we develop and theoretically verify a grease life test machine for ball bearings. We conduct a life test of grease according to various operating conditions of bearings and predict the grease life with a 10% and 50% failure probability using the Weibull analysis. In addition, we analyze the oxide characteristics of the grease over time using the Fourier transform infrared spectroscopy and the deterioration characteristics of the grease using the carbonyl index.","grease life evaluation(그리스의 수명평가), ball bearing(볼 베어링), grease life test machine(그리스 수명시험기), weibull(와이불), FT-IR(적외선 분광분석)","손정훈1ㆍ김세웅2ㆍ최병호3ㆍ이승표4†\n1㈜일진베어링 기술연구소 고분자재료연구팀 책임연구원, 2㈜일진글로벌 기술연구소 고분자재료연구팀 팀장, 3고려대학교 기계공학과 교수, 4(주)일진글로벌 기술연구소 이사","https://doi.org/10.9725/kts.2020.37.1.7"]
["37권1호\npp.18-26","열 경계 조건이 다른 틸팅패드저널베어링의 성능\n(Performance of Tilting Pad Journal Bearings with DifferentThermal Boundary Conditions)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This study shows the effect of the thermal boundary condition around the tilting pad journal bearing on the static and dynamic characteristics of the bearing through a high-precision numerical model. In many cases, it is very difficult to predict or measure the exact thermal boundary conditions around bearings at the operating site of a turbomachine, not even in a laboratory. The purpose of this study is not to predict the thermal boundary conditions around the bearing, but to find out how the performance of the bearing changes under different thermal boundary conditions. Lubricating oil, bearing pads and shafts were modeled in three dimensions using the finite element method, and the heat transfer between these three elements and the resulting thermal deformation were considered. The Generalized Reynolds equation and three-dimensional energy equation that can take into account the viscosity change in the direction of the film thickness are connected and analyzed by the relationship between viscosity and temperature. The numerical model was written in in-house code using MATLAB, and a parallel processing algorithm was used to improve the analysis speed. Constant temperature and convection temperature conditions are used as the thermal boundary conditions. Notably, the conditions around the bearing pad, rather than the temperature boundary conditions around the shaft, have a greater influence on the performance changes of the bearing.","thermal boundary condition(열경계조건), tilting pad journal bearing(틸팅패드 저널베어링), generalized reynolds equation(일반화된 레이놀즈방정식), energy equation(에너지방정식), heat transfer(열전달)","서준호1ㆍ황철호2†\n1부산대학교 기계공학부 조교수, 2한남대학교 기계공학과 교수","https://doi.org/10.9725/kts.2020.37.1.14"]
["37권1호\npp.27-33","초음파나노표면개질기술로 제작된 마이크로 그루브가미끄럼 마찰 특성에 주는 영향\n(Effect of Micro-grooves Manufactured via UltrasonicNanocrystalline Surface Modification on Sliding Friction)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","The surface texture produced via surface texturing is an important approach for controlling the tribological behavior of friction behavior of mechanical devices. The purpose of this study is to investigate the effect of grooves generated via ultrasonic nanocrystal surface modification (UNSM) technology on the tribological performance of AISI 4150 steel against stainless steel 316L. In the study, tribological tests are performed under two different regimes, namely mixed and hydrodynamic lubrication, by varying the applied normal load and reciprocating speed during the tests. According to the test results, the friction coefficient decreases as static load (10 N, 30 N, and 50 N) of UNSM technology increases in the mixed lubrication regime. Conversely, the friction coefficient increases as the static load (10 N, 30 N, and 50 N) of UNSM technology increases in the hydrodynamic lubrication regime. Hence, the results indicate that micro-grooves generate hydrodynamic pressure in the outlet, which increases the oil film thickness between the two mating surfaces. This potentially leads to a reduction in friction in the mixed lubrication regime due to the prevention of contact of asperities and debris. However, the results indicate an adverse effect in the hydrodynamic lubrication regime. In this regard, additional experiments should be performed to investigate the effect of grooves generated by UNSM technology at varying conditions on the friction behavior of AISI 4150 steel, which in turn can be controlled by the generated pressure and oil film thickness at the contact interface.","groove(그루브), sliding friction(미끄럼 마찰), UNSM(초음파나노표면개질)","노준석1ㆍ아마노프 아웨즈한2†\n1선문대학교 대학원 융합과학기술학과 석사과정생, 2선문대학교 기계공학과/융합과학기술학과 부교수","https://doi.org/10.9725/kts.2020.37.1.25"]
["37권1호\npp.34-38","스러스트 래버린스 실을 배면에 갖는 원심형 임펠러의 축력 해석\n(Analysis of the Axial Thrust Force of a Centrifugal Impeller with a Thrust Labyrinth Seal at its Backside)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This study describes the effects of a thrust labyrinth seal applied to the backside of a centrifugal impeller on the axial thrust force for high speed turbomachinery. The bulk flow model using Neumann’s equation calculates the seal cavity pressures and leakage flow rate of the thrust labyrinth seal based on three configurations: teeth-on-rotor (TOR), teeth-on-stator (TOS), and interlocking labyrinth seal (ILS). Prediction results show that the ILS is superior to the TOR and TOS in terms of leakage flow rate. A mathematical model of a centrifugal impeller with a thrust labyrinth seal on its backside calculates the force components corresponding to the impeller inlet, shroud, impeller backside outer, backside seal, and backside inner pressures. A summation of the force components renders the total axial thrust force acting on the centrifugal impeller. The Newton-Raphson numerical scheme iteratively calculates the pressures and leakage flow rate through the impeller wall gap. The prediction results reveal that the leakage flow rate and total axial thrust force increase with rotor speed, and the ILS significantly decreases the leakage flow rate, whereas it slightly increases the axial thrust force when compared to TOR and TOS. Increasing the seal clearance causes an increase in the leakage flow rate and a slight decrease in the axial thrust force with the ILS.","labyrinth seal(래버린스 실), leakage flow rate(누설 유량), pressure drop(압력 강하), axial thrust force(축력), centrifugal impeller(원심형 임펠러)","박준혁1ㆍ김태호2†\n1국민대학교 대학원 기계설계학과 석사과정생, 2국민대학교 기계공학부 교수","https://doi.org/10.9725/kts.2020.37.1.31"]
["37권2호\npp.41-47","유전상수 센서를 이용한 유압 작동유의 분석을 위한 실험장비 개발\n(Development of Experimental Device for Analysis of Hydraulic Oil Characteristics with Dielectric Constant Sensors)","Condition Monitoring & Maintenance System (System Reliability)","An experimental device was developed for analysis of hydraulic oil characteristics with dielectric constant sensors. Online analysis is the most effective method of the three methods used for analyzing lubricant oils. This is because it can monitor the machine condition effectively using oil sensors in real time without requiring excellent analysis skill and eliminates human errors. Determining the oil quality usually requires complex laboratory equipment for measuring factors such as density, viscosity, base number, acid number, water content, additive, and wear debris. However, the electric constant is another indicator of oil quality that can be measured on-site. The electric constant is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has a vacuum as its dielectric. The electric constant affects the factors such as the base oil, additive, temperature, electric field frequency, water content, and contaminants. In this study, the tendency of the electric constant is investigated with a variation of temperature, water content, and dust weight. The experimental device can control working temperature and mix the contaminants with oil. A machine condition monitoring program developed to analyze hydraulic oil is described. This program provides graph and digital values with variation of time. Moreover, it includes an alarm system for when the oil condition is bad.","dielectric constant(유전상수), hydraulic oil(유압 작동유), machine condition monitoring(기계상태진단)","홍성호†\n동국대학교 창의융합공학부 기계시스템공학전공 조교수","https://doi.org/10.9725/kts.2021.37.2.41"]
["37권2호\npp.48-53","풍력발전용 피치 드라이브 시스템의 복합 유성기어류에 대한 피로 강도해석\n(Fatigue Strength Analysis of Complex Planetary Gear Trainof the Pitch Drive System for Wind Turbines)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ,Others","Wind energy is considered as the most competitive energy source in terms of power generation cost and efficiency. The power train of the pitch drive for a wind turbine uses a 3-stage complex planetary gear system in being developed locally. A gear train of the pitch drive consists of an electric or hydraulic motor and a planetary decelerator, which optimizes the pitch angle of the blade for wind generators in response to the change in wind speed. However, it is prone to many problems, such as excessive repair costs in case of failure. Complex planetary gears are very important parts of a pitch drive system because of strength problem. When gears are designed for the power train of a pitch drive, it is necessary to analyze the fatigue strength of gears. While calculating the specifications of the complex planetary gears along with the bending and compressive stresses of the gears, it is necessary to analyze the fatigue strength of gears to obtain an optimal design of the complex planetary gears in terms of cost and reliability. In this study, the specifications of planetary gears are calculated using a self-developed gear design program. The actual gear bending and compressive stresses of the planetary gear system were analyzed using the Lewes and Hertz equation. Additionally, the calculated specifications of the complex planetary gears were verified by evaluating the results from the Stress - No. of cycles curves of gears.","wind turbine(풍력 발전기), pitch drive(피치 드라이브), planetary gear train(유성기어 트레인), gear bending stress(기어 굽힘 응력), gear compressive stress(기어 면압 응력)","김광민1ㆍ배명호2ㆍ조연상3†\n1우림기계 기술개발센터 이사, 2창원문성대학교 항공정비학부 교수, 3동아대학교 기계공학과 조교수","https://doi.org/10.9725/kts.2021.37.2.48"]
["37권2호\npp.54-61","WC위 TiAlN 코팅층에 미치는 Sand Blasting 처리의 영향\n(Effects of Sand Blasting on TiAlN Coating on WC Hard Metal Alloy Tip)","Tribology in Design & Manufacturing (Metalworking / Machining) ","The effect of the sand blasting before TiAlN coating in the manufacture of WC hard metal alloy tips have been studied. For four different tips, according to the status of processing of the sand blasting and the coating, residual stress measurement by X-ray diffraction and several tests for mechanical properties have been conducted. The results suggest that there was no difference in static mechanical properties, such as hardness, surface roughness and elastic modulus, between two coatings. Furthermore, compressive residual stress was generated equally on their surfaces. Additionally, the compressive residual stress in substrate WC was found to increase greatly when subjected to sand blasting treatment. However, the compressive residual stress decrease after coating regardless of sand blasting treatment. Nevertheless, it is confirmed that the compressive residual stress generated in the coating after sand blasting is less than that in the non-sandblasting coating. This was attributed to the plastic deformation occurring in the WC substrate during coating after sand blasting. In contrast to the scratch test results, sand blasting was assumed to have a negative effect on the adhesion between the coating and substrate. This is because there is a high possibility of microcracks due to plastic deformation in the WC substrate under the coating after sand blasting.","residual stress(잔류응력), sand blasting(샌드 블라스팅), WC(텅스텐카바이드), TiAlN coating(TiAlN 코팅), plastic deformation(소성변형)","이한영†\n계명대학교 신소재공학과 교수","https://doi.org/10.9725/kts.2021.37.2.54"]
["37권2호\npp.62-70","Ni-25at.%Al 금속간화합물의 연소합성반응에 미치는사전 Annealing 처리의 영향\n(Effects of Pre-Annealing Treatment on the Combustion Synthesis of Ni3Al Intermetallics Coating)","Tribology in Design & Manufacturing (Metalworking / Machining) ","The problem with intermetallics coating using the heat of molten casting is that the heat generated\uffffﾠ\uffffﾠ\nduring combustion synthesis dissolves the coating and the substrate metal. This study investigates whether pre-annealing before synthesis can control the reaction heat, with the aim of Ni3Al coating on the casting surface. Therefore, the effects of the annealing temperature and time on the combustion synthesis behavior of the powder compact of Ni-25at%Al after annealing were investigated. As results, the reaction heat when synthesized decreased as the annealing temperature was high and the annealing time was longer. This was attributed to the fact that Al was diffused to Ni particles during low temperature annealing and intermediate Ni-Al compounds were formed during high temperature annealing. After combustion synthesis, however, it was found that their microstructures were almost identical except for the amount of intermediate intermetallics. Furthermore, an annealing temperature above 450oC, at which intermediate compounds begin to form, is needed to prevent the dissolving problem during synthesizing. The intermetallics synthesized after annealing at higher temperature and prolonger annealing time showed a good wear resistance. This might be because much intermediate intermetallics of high hardness were remained in the microstructure.","reaction heat(반응열), heat of molten casting(용탕열), coating(코팅), pre-annealing(사전어닐링),\ncombustion synthesis(연소합성)","이한영1†ㆍ모남규2\n1계명대학교 신소재공학과 교수, 2계명대학교 대학원 재료공학과 석사졸업생","https://doi.org/10.9725/kts.2021.37.2.62"]
["37권2호\npp.71-76","액체-고체 접촉대전을 위한 PET 기판 기반 ODA/PDMS딥 코팅 제조 및 평가\n(Synthesis and Evaluation of Superhydrophobic ODA/PDMSDip Coating on PET for Liquid-Solid Contact Electrification)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","As opposed to using fossil fuels, we need to use eco-friendly resources such as sunlight, raindrops and wind to produce electricity and combat environmental pollution. A triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electricity by inducing repetitive contact and separation of two dissimilar materials. During the contact and separation processes, electron flow occurs owing to a change in electric potential of the contacting surface caused by contact electrification and electrostatic induction mechanisms. A solid-solid contact TENG is widely known, but it is possible to generate electricity via liquid-solid contact. Therefore, by designing a hydrophobic TENG, we can gather electricity from raindrop energy in a feasible manner. To fabricate the superhydrophobic surface of TENGs, we employ a dip coating technique to synthesize an octadecylamine (ODA)- and polydimethylsiloxane (PDMS)-based coating on polyethylene terephthalate (PET). The synthesized coating exhibits superhydrophobicity with a contact angle greater than 150° and generates a current of 2.2 μA/L while water droplets fall onto it continuously. Hence, we prepare a box-type TENG, with the ODA/PDMS coating deposited on the inside, and place a 1.5 mL water droplet into it. Resultantly, we confirm that the induced vibration causes continuous impacts between the ODA/PDMS coating and the water, generating approximately 100 pA for each impact.","wettability(젖음성), superhydrophobicity(초소수성), contact angle(접촉각), dip coating(딥 코팅), triboelectric nanogeneroator(마찰전기 나노발전기)","박선영1ㆍ강현규2ㆍ변도영3ㆍ조대현4†\n1성균관대학교 기계공학부 공학연구원, 2성균관대학교 기계공학부 학사과정, 3성균관대학교 기계공학부 교수, 4경상국립대학교 메카트로닉스공학부 조교수","https://doi.org/10.9725/kts.2021.37.2.71"]
["37권2호\npp.77-80","나노스케일 마찰거동에서 스프링 상수가 마찰에 미치는 영향에 대한 분자동역학 연구\n(Study on Influence of Spring Constant on Frictional Behaviorat the Nanoscale through Molecular Dynamics Simulation)","Modeling & Simulation in Tribology","In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick–slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases.","spring constant(스프링 상수), friction(마찰), molecular simulation(분자 시뮬레이션), stick-slip(스틱슬립)","강원빈1ㆍ김현준2,3†\n1경북대학교 미래과학기술융합학과 석사과정생, 2경북대학교 정밀기계공학과 부교수, 3경북대학교 미래과학기술융합학과 부교수","https://doi.org/10.9725/kts.2021.37.2.77"]
["37권3호\npp.83-90","표면개질 기술에 의한 Cu 기반 바이메탈의 인장강도,스크래치 저항성 및 트라이볼로지 성능 향상\n(Improvement in Tensile Strength, Scratch Resistance and Tribological Performance of Cu-based Bimetals by Surface Modification Technology)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification)","In this study, an ultrasonic nanocrystal surface modification (UNSM) was used to improve the mechanical properties, scratch resistance and tribological performance of Cu-based bimetals, which are usually used to manufacture sliding bearings and bushings for internal combustion engines (ICEs). Two different Cu-based bimetals, namely CuPb10Sn10 and CuSn10Bi7, were sintered onto a low carbon steel substrate. The mechanical properties and dry tribological performance using a tensile tester and micro-tribo tester were evaluated, respectively. The scratch resistance was assessed using a micro-scratch tester at an incremental load. The tensile test results showed that the yield strength (YS) and ultimate tensile strength (UTS) of both Cu-based bimetals increased after UNSM. Furthermore, the scratch and tribological tests results revealed that the scratch resistance and tribological performance of both Cu-based bimetals were improved by the application of UNSM. These improvements were mainly attributed to the eliminated pores, increased hardness and reduced roughness after UNSM. CuSn10Bi7 demonstrated better mechanical properties, scratch resistance and tribological performance than CuPb10Sn10. It was found that the presence of Bi in CuSn10Bi7 formed a Cu11Bi7 intermetallic phase, which is harder than Cu3Sn. Hence, CuSn10Bi7 demonstrated higher strength and wear resistance than CuPb10Sn10. In addition, a CuSn10Bi7 formed both SnO2 and Bi2O3 that prevented adhesion and improved the tribological performance. It can be expected that under dry tribological conditions, ICEs can utilize UNSM bearings and bushings made of CuSn10Bi7 instead of CuPb10Sn10 under oil-lubricated conditions.","bimetal(바이메탈), porosity(기공), tensile strength(인장강도), sliding friction(미끄럼마찰), sliding wear(미끄럼마모), surface modification(표면개질)","카림바예프 루슬란1ㆍ아마노프 아웨즈한2\n1선문대학교 대학원 융합과학기술학과 박사과정생, 2선문대학교 기계공학과/융합과학기술학과 부교수","https://doi.org/10.9725/kts.2021.37.3.83"]
["37권3호\npp.91-98","정압 베어링을 적용한 수소 액화 공정용 터보 팽창기 개발\n(Development of Turbo Expanders with Hydrostatic Bearingsfor Hydrogen Liquefaction Plants)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","This paper presents a hydrostatic bearing design and rotordynamic analysis of a turbo expander for a hydrogen liquefaction plant. Th~e turbo expander includes the turbine and compressor wheel assembled to a shaft supported by two hydrostatic radial and thrust bearings. The rated speed is 75,000 rpm and the rated power is 6 kW. For the bearing operation, we use pressurized air at 8.5 bar as the lubricant that is supplied to the bearing through the orifice restrictor. We calculate the bearing stiffness and flow rate for various gauge pressure ratios and select the orifice diameter providing the maximum bearing stiffness. Additionally, we conduct a rotordynamic analysis based on the calculated bearing stiffness and damping considering design parameters of the turbo expander. The predicted Cambell diagram indicates that there are two critical speeds under the rated speed and there exists a sufficient separation margin for the rated speed. In addition, the predicted rotor vibration is under 1 μm at the rated speed. We conduct the operating test of the turbo expander in the test rig. For the operation, we supply pressurized air to the turbine and monitor the shaft vibration during the test. The test results show that there are two critical speeds under the rated speed, and the shaft vibration is controlled under 2.5 μm.","hydrostatic bearing(정압베어링), turbo expander(터보팽창기), orifice(오리피스), hydrogen liquefaction(수소액화)","이동현1†ㆍ김병옥1ㆍ박무룡2ㆍ임형수2\n1한국기계연구원 시스템다이나믹스연구실 책임연구원, 2한국기계연구원 에너지변환기계연구실 책임연구원","https://doi.org/10.9725/kts.2021.37.3.91"]
["37권3호\npp.99-105","Stability Characteristics of Supercritical High-Pressure Turbines Depending on the Designs of Tilting Pad Journal Bearings","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","In this study, for a high-pressure turbine (HPT) of 800 MW class supercritical thermal-power plant, considering aerodynamic cross-coupling, we performed a rotordynamic logarithmic decrement (LogDec) stability analysis with various tilting pad journal bearing (TPJB) designs, which several steam turbine OEMs (original equipment manufacturers) currently apply in their supercritical and ultra-supercritical HPTs. We considered the following TPJB designs: 6-Pad load on pad (LOP)/load between pad (LBP), 5-Pad LOP/LBP, Hybrid 3-Pad LOP (lower 3-Pad tilting and upper 1-Pad fixed), and 5-Pad LBPs with the design variables of offset and preload. We used the API Level-I method for a LogDec stability analysis. Following results are summarized only in a standpoint of LogDec stability. The Hybrid 3-Pad LOP TPJBs most excellently outperform all the other TPJBs over nearly a full range of cross-coupled stiffness. In a high range of cross-coupled stiffness, both the 6-Pad LOP and 5-Pad LOP TPJBs may be recommended as a practical conservative bearing design approach for enhancing a rotordynamic stability of the HPT. As expected, in a high range of cross-coupled stiffness, the 6-Pad LBP TPJBs exhibit a better performance than the 5-Pad LBP TPJBs. However, contrary to one’s expectation, notably, the 5-Pad LOP TPJBs exhibit a slightly better performance than the 6-Pad LOP TPJBs. Furthermore, we do not recommend any TPJB design efforts of either increasing a pad offset from 0.5 or a pad preload from 0 for the HPT in a standpoint of stability.","cross-coupled stiffness, LogDec stability, supercritical high-pressure turbine, tilting pad journal bearing.","An Sung Lee1† and Sun-Yong Jang2\n1Principal Researcher, Dept. of System Dynamics Research, Division of Mechanical Systems Safety Research,Korea Institute of Machinery & Materials, 2Director, R&D Center, Daedong Metal Industry Co.","https://doi.org/10.9725/kts.2021.37.3.99"]
["37권3호\npp.106-111","액체금속(GaInSn)윤활하에서 DLC(ta-C) 코팅된 레이저표면 텍스쳐링 딤플패턴의 미끄럼 마찰특성평가\n(Evaluation of Sliding Friction Properties of Laser Surface Texturing Dimple Pattern with DLC Coating under GaInSn Liquid Metal Lubricant)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","There are several studies on reducing the friction that occurs on the relative sliding contact surface of moving parts under extreme environments. In particular, a solid lubricated bearing is studied to solve the tribological problem with friction reduction and durability parts using solid lubricants (lead or silver) in a vacuum atmosphere. Galinstan is mainly used as a liquid metal lubricant, but it is inevitable to have limited tribological applications owing to its high coefficient of friction. Many researchers work on surface texturing for surface modification and precision processing methods. To increase durability and low friction, DLC coating with hydrophobicity is applied on the contact surface texture. Therefore, using an untextured specimen, a dimple specimen, and a DLC-coated dimple specimen under liquid metal lubrication, this paper presents the following experimental sliding friction characteristics in the sliding friction test. 1) The average coefficient of friction of the DLC-coated dimple specimen and dimple specimen are lower compared to that of a non-patterned specimen. 2) In the DLC-coated dimple specimens, the average coefficient of friction changes according to the change in the dimple density. 3) DLC-coated dimple specimens with a density of 12.5 have the lowest average coefficient of friction under 41.6 N of normal load and 143.3 RPM.","dimple pattern(딤플 패턴), DLC(diamond like carbon), laser surface texturing(레이저 표면 텍스쳐링), liquid metal lubricant(액체 금속 윤활), sliding friction(미끄럼 마찰)","권규빈1ㆍ장영준2ㆍ채영훈3†\n1경북대학교 금속신소재공학과 학부생, 2한국재료연구원 책임연구원, 3경북대학교 공학설계연구소 연구교수","https://doi.org/10.9725/kts.2021.37.3.106"]
["37권3호\npp.112-116","충돌 해석 시 마찰 모델 적용을 위한 기초 마찰 시험 연구\n(Feasibility Study of Friction Characteristics for Impact Analysis)","Modeling & Simulation in Tribology","Appropriate friction model usage is important for impact analysis because the relative motions between parts that are in contact for very short durations can vary greatly depending on the friction model. Vehicle seat components that have significant effects on impact analysis are also considered. This paper presents an experimental investigation of various material contact pairs to obtain the friction parameters of the Benson exponential friction model for impact simulation. The Coulomb friction model has limitations for impact analysis because of singularity at zero velocity. Metal/nonmetal materials are prepared, and friction tests are conducted for various sliding speeds, loads, and lubrication conditions. The obtained data are used in the friction model to implement finite element analysis. The parameters of the friction model are obtained by the curve-fitting method. The experimental results show that the friction coefficient with metal/nonmetal contact pairs is stable regardless of the working conditions. The friction model used in this study can also be applied for finite element analysis of the crash conditions, where the friction changes abruptly at the contact interface; the obtained friction parameters are also expected to be more accurate with more precise tests under different working conditions. These results can help improve the accuracy of the finite element analysis.","friction(마찰), friction model(마찰모델), lubrication(윤활), friction decay constant(마찰 감쇄 계수)","이광희1ㆍ이철희2†\n1인하대학교 대학원 기계공학과 박사과정생, 2인하대학교 기계공학과 교수","https://doi.org/10.9725/kts.2021.37.3.112"]
["37권4호\npp.117-124","에어 포일 스러스트 베어링의 탑포일 경사면 형상이유동특성에 미치는 영향에 대한 수치해석 연구\n(The Effects of Inclined Foil Shape on Flow Characteristicsin Air Foil Thrust Bearing Using CFD)","Modeling & Simulation in Tribology","In this study, we perform a 3D CFD conjugate analysis according to the shape of the foil ramp of the air foil thrust bearing, analyze the flow characteristics inside the bearing, and compare the results corresponding to the two shapes. Air has a lower viscosity than lubricating oil. Therefore, the thrust runner of the bearing must rotate at high speed to support the load. The gap between thrust runner and foil is significantly smaller than that of the oil bearing. Hence, it is crucial to analyze the complex flow characteristics inside the bearing to predict the complex flow inside the bearing and performance of the bearing. In addition, flow characteristics may appear differently depending on the ramp shape of the bearing foil, which may affect bearing performance. In this study, we numerically analyze the main flow path of air flowing into the bearing and the secondary flow path used for cooling the bearing using the commercial CFD software ANSYS CFX and compare the flow characteristics for straight and curved foil ramp shapes. Notably, there is a difference in the speed of the flowing air according to the shape of the ramp, which affects the bearing performance.","air foil thrust bearing(에어 포일 스러스트 베어링), computational fluid dynamics(전산유체역학), hydrodynamic lubrication(유체윤활), load capacity(하중지지능력), leakage rate(누설 유량)","백건웅1ㆍ주원구2†ㆍ문형욱3ㆍ황성현4ㆍ정성윤3ㆍ박정구5\n1연세대학교 대학원 기계공학과 석사과정생, 2연세대학교 기계공학과 교수, 3한화파워시스템 연구원, 4한화파워시스템 책임연구원, 5한화파워시스템 수석연구원","https://doi.org/10.9725/kts.2021.37.4.117"]
["37권4호\npp.125-128","육방정질화붕소 나노플레이크/폴리이미드 복합체를 이용한마찰전기 나노발전기 평가\n(Evaluation of h-BN Nanoflakes/Polyimide Compositesfor a Triboelectric Nanogenerator)","Eco/Green Tribology (Renewable / Alternative Energies)","A means of enhancing the performance of triboelectric nanogenerators (TENGs) is increasing the differences in work functions between contacting materials. Hexagonal boron nitride (h-BN) exhibits excellent mechanical properties and high chemical stability as well as a high work function. As a result, engineers in the field of energy harvesting have envisioned using h-BN in the electrification layer in TENGs. For the industrial application of h-BN in TENGs, large-scale production is necessary, and h-BN is generally exfoliated and dispersed in various solvents. In this study, we evaluate the performance of a TENG with h-BN nanoflakes in the polyimide (PI) layer. To synthesize a PI composite containing h-BN nanoflakes, h-BN powders are exfoliated and dispersed in poly(amic acid) (PAA), which is the precursor of PI. Then, h-BN dispersion is spin-coated onto the PI film and cured for 2 h under 300oC. This composite material can then be used for the electrification layer in TENGs. Below the electrification layer, an aluminum foil is placed and used as an electrode. When the contact and separation processes with polyethylene terephthalate are repeated, the fabricated TENG shows a maximum power density of 190.8 W/m2. This study shows that h-BN is a promising material for enhancing the performance of the electrification layer in TENGs.","hexagonal boron nitride(육방정 질화붕소), polyimide(폴리이미드), triboelectric nanogenerator(마찰전기 나노발전기)","박선영1ㆍ변도영2ㆍ조대현3†\n1성균관대학교 기계공학부 공학연구원, 2성균관대학교 기계공학부 교수, 3경상국립대학교 메카트로닉스공학부 조교수","https://doi.org/10.9725/kts.2021.37.4.125"]
["37권4호\npp.129-135","포켓의 깊이가 공기 베어링 스테이지의 햄머링 현상에 미치는 영향\n(Effect of the Pocket Depth on the Hammering Behaviorof an Air Bearing Stage)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","An air-bearing stage uses externally pressurized air as the lubricant between the stage and the rail. The supporting force generated by the supplied air makes the stage rise and move smoothly with extremely low friction. Mechanical contacts rarely happen, the bearing surfaces do not produce wear particles, and dust is not generated. It also has the advantage of having low energy loss and high precision. Because of its advantages, an air-bearing stage is used in several types of machines that require high precision. In this article, the effect of the pocket depth on the hammering phenomena of the air bearing is studied. An analysis program is developed to calculate the dynamic behavior of the stage by solving the Reynolds equation between the stage and the guideway and the equations of motion on the stage. The acceleration, constant movement, and deceleration are applied to the stage. The stage is modeled as a five-degree-of-freedom system. In the course of the dynamic behavior, the hammering phenomena occur under some special conditions. The deeper the pocket, the more unstable the behavior of the stage, and air hammering occurs when it exceeds a certain depth. In addition, the higher the supply pressure, the more unstable the behavior of the stage. However, hammering occurs even with a shallow pocket depth. Other conditions that affect the hammering phenomena are calculated and discussed.","air bearing stage(공기베어링 스테이지), clearance(틈새), hammering(햄머링), pocket depth(포켓 깊이)","이춘무1ㆍ김규하2ㆍ박상준3ㆍ황규진4ㆍ박상신5†\n1㈜트리엔 대표이사, 2(주)트리엔 연구소장, 3영남대학교 대학원 기계공학과 석사졸업생, 4영남대학교 대학원 기계공학과 석사과정생, 5영남대학교 기계공학부 교수","https://doi.org/10.9725/kts.2021.37.4.129"]
["37권4호\npp.136-143","체결력을 고려한 내부 및 외부연결형 임플란트의반복 하중에 대한 풀림 연구\n(Loosening behavior of Internal and External Connection Dental Implants under Cyclic Loads Considering Pre-fastening Force)","Contact Mechanics & Friction ","This paper presents the loosening behavior that occurs after the application of an external load to internal and external connection types of dental implants using the finite element method. We use fastening force between an abutment and a fixture to clamp the dental implant system; however, loosening and breakage may occur owing to cyclic external loads. In this study, we considered the initial fastening condition in the pre-load analysis and then investigated the change in stress and contact surface status when applying external loads. After the application of the initial fastening load, we verified that the internal connection-type model exhibited a relatively lower stress distribution than that of the external connection-type one. Moreover, we found that the former model showed a lower stress concentration after the application of the external load. In addition, after the application of this load, we found that the higher the shear load acting on the implant system, the higher the possibility of loosening. The study results showed the change in stress distribution and contact surface according to the connection type of the dental implants and the phenomenon of loosening by cyclic loads. We expect that the results of this study will be useful for the study of reliability and design of dental implant systems.","dental implant(치과용 임플란트), abutment-implant connection(지대주 연결 방식), FEM(유한요소법), srew loosening(나사 풀림), fastening force(체결력), cyclic load(반복 하중)","이용우1ㆍ장용훈2†\n1신한대학교 기계자동차융합공학과 조교수, 2연세대학교 기계공학부 교수","https://doi.org/10.9725/kts.2021.37.4.136"]
["37권4호\npp.144-150","유한요소해석에 의한 코팅면의 브리넬 경도 평가:제2보 - 모재와 코팅두께의 영향\n(Evaluation of Brinell Hardness of Coated Surfaceby Finite Element Analysis:Part 2 - Influence of Substrate and Coating Thickness)","Contact Mechanics & Friction, Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ","The most cost-effective method of reducing abrasive wear in mechanical parts is increasing their hardness with thin hard coatings. In practice, the composite hardness of the coated substrate is more important than that of the substrate or coating. After full unloading of the load applied to an indenter, its indentation hardness evaluated based on the dent created on the test piece was almost dependent on plastic deformation of the substrate. Following the first part of this study, which proposes a new Brinell hardness test method for a coated surface, the remainder of the study is focused on practical application of the method. Indentation analyses of a rigid sphere and elastic-perfect plastic materials were performed using finite element analysis software. The maximum principal stress and plastic strain distributions as well as the dent shapes according to the substrate yield stress and coating thickness were compared. The substrate yield stress had a significant effect on the dent size, which in turn determines the Brinell hardness. In particular, plastic deformation of the substrate produced dents regardless of the state of the coating layer. The hardness increase by coating behaved differently depending on the substrate yield stress, coating thickness, and indentation load. These results are expected to be useful when evaluating the composite hardness values of various coated friction surfaces.","Brinell hardness(브리넬 경도), coating(코팅), indentation analysis(압입해석), finite element analysis(유한요소해석), yield stress(항복응력)","박태조1†ㆍ강정국2\n1경상국립대학교 기계공학부 교수 · 공학연구원, 2경상국립대학교 대학원 기계항공공학부 석사과정","https://doi.org/10.9725/kts.2021.37.4.144"]
["37권5호\npp.151-163","그래핀의 나노스케일 마찰 및 표면 특성에 대한 연구동향\n(Research Trends in the Nanoscale Friction and SurfaceCharacteristics of Graphene)","Micro/Nano-Tribology","Since the discovery of single-layer graphene, exploiting graphene’s excellent physical/chemical properties in tribology systems has been a topic of interest in academia over the last few decades. There is no doubt that understanding the underlying friction mechanism of graphite should precede this. Even now, new properties of graphene are being reported in academia, and based on this, studies exploring the origins of graphene’s surface properties and friction characteristics in a wide range of scales are also being performed. From the perspective of lubrication engineering, graphene research can be largely divided into studies that 1) reveal its basic friction mechanism at the nanoscale and 2) explore its application in macroscale sliding systems. At the nanoscale, the basic friction mechanism of graphene is mainly due to its atomic thickness. In this paper, the various research on the nanoscale friction and surface characteristics of graphene is reviewed. Graphene surface properties, such as wettability and surface energy and the basic friction mechanisms of graphene attributed to adhesion, electron-phonon scattering, bending stiffness, and the underlying substrate, are summarized. Further, we provide the research outcomes on the superlubricity of graphene. Finally, the potential application and challenges of the superlubricity of graphene are highlighted. Through this, we intend to provide summarized information to researchers interested in the tribological properties of graphene and help set the direction of future research.","graphene(그래핀), friction(마찰), surface characteristics(표면 특성), superlubricity(초윤활성)","윤민아1,2ㆍ김광섭3,4†ㆍ조대현5‡\n1한국과학기술연합대학원대학교 나노메카트로닉스학과 박사과정생, 2한국기계연구원 나노융합장비연구부 학생연구원, 3한국과학기술연합대학원대학교 나노메카트로닉스학과 교수, 4한국기계연구원 나노융합장비연구부 책임연구원, 5경상국립대학교 메카트로닉스공학부 부교수","https://doi.org/10.9725/kts.2021.37.5.151"]
["37권5호\npp.164-171","초음파 센서의 1차 정합층 두께에 따른 가스탱크 미세누설 수신특성\n(Gas Tank Microleakage Reception Characteristics According to Thickness of the First Matching Layer of Ultrasonic Sensor)","Automotive Tribology","Ultrasonic sensors show various reception characteristics based on the density of the measurement medium; hence, they are used in various fields to benefit from the characteristics of ultrasonic signals. In this study, the reception characteristics according to the thickness of the first matching layer are compared and analyzed for application to gas tank microleak detection. Accordingly, three types of sensors are manufactured with varying thicknesses of the first matching layer, namely 4.8 mm, 5.1 mm, and 5.5 mm; further, a direct measurement method is used wherein the sensor is attached to the inside of the chamber. Experiments are conducted to observe the phase change due to microleakage, which is the most linear in the sensor with the 4.8 mm thick first matching layer. This is assumed to be the result of stable signal transmission and reception with little phase deviations over time because the first matching layer is closest to the ultrasonic wavelength. The other sensors show nonlinear results with increasing thickness of the first matching layer. Through this study, it is found that appropriately selecting the thickness of the first matching layer of the ultrasonic sensor can greatly influence sensor reliability.","gas density(가스 밀도), gas fuel(가스 연료), gas storage(가스 저장소), microleakge(미세 누설), ultrasonic sensor(초음파 센서)","서원준1ㆍ손성진2ㆍ임석연3†\n1충남대학교 대학원 기계공학과 박사과정생, 2충남대학교 대학원 융복합시스템공학과 석사과정생, 3충남대학교 기계 · 재료공학교육과 부교수","https://doi.org/10.9725/kts.2021.37.5.164"]
["37권5호\npp.172-178","고압 인젝터의 동적 거동을 고려한 최적 틈새 조합에 관한 연구\n(Selection of Optimum Clearance Considering the Dynamic Behavior of a High-pressure Injector)","Bearing / Seal / Gear Tribology (Tribology of Machine Elements) ","An injector is a mechanical device present inside the engine. Its main function is to supply an appropriate volume of fuel into the combustion chamber, which is directly related to the overall engine efficiency of a car. During the operation of an injector, a magnetic force lifts the parts of the injector from closed position to open position which generates a horizontal force on the needle. The horizontal force acts on a different position from that of the center of mass of the needle. Therefore, this causes eccentricity in the needle and the generation of a tilting motion during the lifting operation which can result in wear. However, appropriate selection of clearances for these parts can prevent wear. In this study, lubrication analysis is conducted to determine the optimum clearance of parts with sliding motion inside the injector. The height functions are derived considering the dynamic behavior and relative velocity of the parts. Using the derived height function, the pressure profiles are calculated for the lubricated surfaces from the Reynolds' equation. Subsequently, the fluid reaction forces are calculated. The equations of motions are applied to the fluid reaction forces and external forces are solved to calculate the minimum film thickness between each part with variation in the clearances. Finally, the optimum clearances are determined. The effect of the clearances on the behavior of the moving parts is presented and discussed.","clearance(틈새), dynamic behavior(동적 거동), height function(높이 함수), high pressure injector(고압 인젝터)","류대원1ㆍ김동준2ㆍ박상신3†ㆍ류봉우4\n1영남대학교 대학원 기계공학과 석사졸업생, 2영남대학교 대학원 기계공학과 석사과정생, 3영남대학교 기계공학부 교수, 4 ㈜현대케피코 책임연구원","https://doi.org/10.9725/kts.2021.37.5.172"]
["37권5호\npp.179-188","Diamond-like Carbon Tribological Endurance usingan Energetic Approach","Contact Mechanics & Friction ,Wear Phenomena & Mechanisms ,Tribo-Testing / Measurement & Instruments ","Reputed for their low friction coefficient and wear protection effect, diamond-like carbon (DLC) materials are considered amongst the most important lubricant coatings for tribological applications. In this framework, this investigation aims to elucidate the effect of a few operating parameters, such as applied stress and sliding amplitude on the friction lifetime of DLC coatings. Fretting wear tests are conducted using a 12.7 mm radius counterpart of 52100 steel balls slid against a substrate of the same material coated with a 2 μm thickness DLC. Approximately, 5 to 57 N force is applied, generating a maximum Hertzian contact pressure of 430 to 662 MPa, corresponding to the applied force. The coefficient of friction (CoF) generates three regimes, first a running-in period regime, followed by a steady-state evolution regime, and finally a progressive increase of the CoF reaching the steel CoF value, as an indicator of reaching the substrate. To track the wear scenario, interrupted tests are performed with analysis combining scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), 3D profilometer and micro-Raman spectroscopy. The results show two endurance values: one characterizing the coating failure (Nc1), and the other (Nc2) indicating the friction failure which is situated where the CoF reaches a threshold value of μth = 0.3 in the third regime. The Archard energy density factor is used to determine the two endurance values (Nc1, Nc2). Based on this approach, a master curve is established delimitating both the coating and the friction endurances.","friction, DLC coatings, fretting wear, Archard energy density factor, tribology","Fathia Alkelae1 and Tea-Sung Jun2†\n1Postdoctoral Research Associate, Dept. of Mechanical Engineering, Incheon National University, 2Associate Professor, Dept. of Mechanical Engineering, Incheon National University","https://doi.org/10.9725/kts.2021.37.5.179"]
["37권5호\npp.189-194","전기화학 에칭 공정을 이용한 스테인리스 스틸 메쉬의방수 특성 연구\n(A Study on Water-Proof Characteristics of a Stainless Steel Mesh by Electrochemical Etching Process)","Surface/Interface Tribology (Treatment & Coatings / Texturing / Modification) ,Micro/Nano-Tribology ","A straightforward, yet effective surface modification method of stainless steel mesh and its interesting anti-wetting characteristics are reported in this study. The stainless steel mesh is electrochemically etched, and the specimen has both micro and nano-scale structures on its surface. This process transforms the two types of mesh specimens known as the regular and dense specimens into hydrophobic specimens without applying any hydrophobic chemical coating process. The fundamental wettability of the modified mesh is analyzed through a dedicatedly designed experiment to investigate the waterproof characteristics, for instance, the penetration threshold. The waterproof characteristics are evaluated in a manner that the modified mesh resists as high as approximately 2.7 times the pressure compared with the bare mesh, i.e., the non-modified mesh. The results show that the penetration threshold depends primarily on the advancing contact angles, and the penetration stop behaviors are affected by the contact angle hysteresis on the surfaces. The findings further confirm that the inexpensive waterproof meshes created using the proposed straightforward electrochemical etching process are effective and can be adapted along with appropriate designs for various practical applications, such as underwater devices, passive valves, and transducers. In general, , additional chemical coatings are applied using hydrophobic materials on the surfaces for the applications that require water-repelling capabilities. Although these chemical coatings can often cause aging, the process proposed in this study is not only cost-effective, but also durable implying that it does not lose its waterproof properties over time.","mesh structure(메쉬 구조물), surface modification(표면 개질), hydrophobic surface(소수성 표면), liquid penetration characteristic(액체 침투 특성), micro/nanostructure(마이크로/나노구조)","이찬1ㆍ김지민2ㆍ김형모3†\n1한국원자력연구원 핵연료안전연구부 선임연구원, 2한국교원대학교 기술교육과 조교수, 3경상국립대학교 기계공학부 조교수","https://doi.org/10.9725/kts.2021.37.5.189"]
["37권5호\npp.195-202","고체표면에 응축된 물 분자의 윤활특성에 대한분자시뮬레이션 연구\n(Lubrication Characteristics of Condensed Water Moleculesat Solid Surface through Molecular Simulation)","Modeling & Simulation in Tribology ","This paper presents a numerical analysis of the lubrication characteristics of condensed water molecules on a solid surface by conducting molecular dynamics simulations. We examine two models consisting of a simple hexahedral substrate with and without water molecules to reveal the lubrication mechanism of mono-layered water molecules. We perform a sliding simulation by contacting and translating a single asperity on the substrate under various normal loads. During the simulation, we measure the friction coefficient and atomic stress. When water molecules were interleaved between solid surfaces, atomic stress exerted on individual atom and friction coefficient were smaller than those of model without water molecule. Particularly, at a low load, the efficacy of water molecules in the reduction of atomic stress and friction is remarkable. Conversely, at high loads, water molecules rarely lubricate solid surfaces and fail to effectively distribute the contact stress. We found a critical condition in which the lubrication regime changes and beyond the condition, significant plastic deformation was created. Consequently, we deduce that water molecules can distribute and reduce contact stress within a certain condition. The reduced contact stress prevents plastic deformation of the substrate and thus diminishes the mechanical interlocking between the asperity and the substrate.","condensation(응축), water molecule(물 분자), lubrication(윤활), molecular simulation(분자 시뮬\n레이션), plastic deformation(소성변형)","김현준1,2†\n1경북대학교 정밀기계공학과 부교수, 2경북대학교 미래과학기술융합학과 부교수","https://doi.org/10.9725/kts.2021.37.5.195"]