• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.63-64
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• 2002

In a micro-scale contact, surface forces such as capillary force and van der Waals Interaction significantly Influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (hydrophilicity), relative humidity and deformation of asperities In the real area of contact. A better understanding of these surface forces is of great necessity in order to find an optimal solution for reducing friction and adhesion of micro surfaces. We proposed an effective method to analyze capillary and van der Waals forces In nano-scale contact. In this method, Winklerian foundation model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height Images. Self-mated contact of diamond-like-carbon (DLC) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidify and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.121-122
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• 2002

This paper presents contact behavior of an Polyperfluoroalkoxyethylene(PTFE) ring seals by a non-linear finite element method using the thermomechanical analysis. PTFE elastomer was assumed as odgen model for numerical analysis in FEM commercial code because elastomer has nonlinear behaviour character. The shape effects are investigated for sealing performance of ring seal in boundary conditions which as gas pressure, groove temperature and various O-ring seal models. Also contact stress and equivalent total strain are investicated. An O-ring seals was modeled four shape which are circle, two sunflower and X. The highest contact stress occurs at sunflower-ring seal with groove deapth of 0.35mm. the equivalent total strain of sunflower-ring seal is lower than that of the others under low gas pressure condition but under gas pressure condition over 4Mpa, that of sunflower-ring seal is higher. The calculated FEM results shows that the Sunflower-ring seal with groove depth of 0.35mm has excellent performance compared with other seal models.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.51-52
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• 2002

We report results on microtribological studies of chemically grafted nanoscale polymer layers of different architecture with thickness below 30 nm. We have fabricated the molecular lubrication coatings from elastomeric tri-block copolymers and tested two different designs of corresponding nanocomposite coatings. We observed a significant reduction of friction forces and an increase of the wear stability when a minute amount of oil was trapped within the grafted polymer layer. These polymer gel layers exhibited a very steady friction response and a small value of the coefficient of friction as compared to the initial polymer coating. A polymer 'triplex' coating has been formed by a multiple grafting technique. The unique design of this layer Includes a hard-soft-hard architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the elastic rubber interlayer.

• Tribology and Lubricants
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• v.26 no.1
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• pp.61-67
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• 2010

The purpose of this paper is to study and analyze the failure examples on tribological characteristics of an automotive steering system. In this failure study, the grease leakage may stick leaked grease, dust, and wear particles between pinion and rack gears in mechanical steering system. In the case of seal failures such as a rod seal, o-ring and oil seals, the gear box and oil pump do not operate properly due to lack of oils. This means that oil pump does not supply a working fluid and produce a normal oil pressure of the steering system. This leads to leak a working fluid from the seals and produce a wear between pinion and rack gears. Especially, the leaked oil is usually mixed with internal wear particles and foreign dust/fine sands. Thus no leakage of working oils is very important design concepts, which is strongly related to the sealing components and smoothly operating of the mechanical friction parts of power steering system.

• Tribology and Lubricants
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• v.21 no.1
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• pp.21-26
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• 2005

Rolling bearings are assorted one of the most important machine elements. The various functions of bearings are greatly influenced by grease, and higher performance of rolling bearing greases is required to improve rolling bearing lubrication. The two conditions for optimum grease synthesis were selected by SSRED (Six Sigma Robust Engineering Design) program by using dropping points and OIT values respectively. And the optimized two urea/ether oil greases were synthesized to compare the performance. The typical physical properties of grease were investigated. And life test of these greases was conducted by rolling bearing grease life tester. The characteristics of the greases before and after life test were investigated using FTIR, microscope, SEM, TG/DSC, OIT and TAN meter. The optimized two greases showed longer life time than typical urea/ether oil grease. The optimized grease by means of OIT value showed higher performance such as long life time, low TAN value and high oil bleeding amount in comparison with the optimized grease using dropping point.

• Journal of Mechanical Science and Technology
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• v.19 no.10
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• pp.1835-1845
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• 2005

In this paper a safe arm with passive compliant joints and visco-elastic covering is designed for human-friendly service robots. The passive compliant joint (PCJ) is composed of a magneto-rheological (MR) damper and a rotary spring. In addition to a spring component, a damper is introduced for damping effect and works as a rotary viscous damper by controlling the electric current according to the angular velocity of spring displacement. When a manipulator interacts with human or environment, the joints and cover passively operate and attenuate the applied collision force. The force attenuation property is verified through collision experiments showing that the proposed passive arm is safe in view of some evaluation measures.

• Tribology and Lubricants
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• v.40 no.4
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• pp.118-132
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• 2024

The triboelectric nanogenerator (TENG) has emerged as a groundbreaking technology for harvesting clean and sustainable energy cost effectively. For reliable TENG design, minimizing wear damage at the friction layers is crucial. This review provides a comprehensive overview of tribometer-integrated TENG testing configurations used in the simultaneous investigation of both tribological and electrical performance. It considers configurations such as plate-on-plate, ball-on-disc, and ball-on-flat tribometers designed for linear reciprocating or rotating sliding friction tests. These tribometers are either specifically designed or adapted for TENG testing. Triboelectric material holders facilitate friction tests by establishing electrical connections from the triboelectric materials or electrodes, thereby enabling accurate measurement of electrical signals. Electrometers and oscilloscopes record electrical outputs such as short-circuit current and open-circuit voltage. This integration enables the simultaneous measurement of both friction and electrical outputs, providing a thorough understanding of TENG performance. The review also summarizes how factors such as normal force, sliding frequency, and rotating speed affect friction coefficients and TENG performance. It also examines the relationship between the coefficient of friction and tribocharges under various loads and frequencies. The review emphasizes the importance of these testing configurations for evaluating both friction and electrical performance, which are crucial for optimizing TENG efficiency. Finally, the review explores future prospects for developing innovative tribometer designs suited for both tribology and TENG testing.

• Tribology and Lubricants
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• v.36 no.4
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• pp.215-231
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• 2020

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 the 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.

• Journal of the Korean Institute of Gas
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• v.15 no.6
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• pp.57-62
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• 2011

In this study, the optimized design for 130 liter storage fuel tank with 70MPa filling pressure has been investigated using a FEM technique and Taguchi design method. The strength safety of a composite fuel tank in which is fabricated by an aluminum liner of 6061-T6 material and carbon fiber wound composite layers of T800-24K has been analyzed based on the criterion of design safety of US DOT-CFFC and Korean Standard. The FEM computed results on the stress safety of 70MPa hydrogen gas tank were compared with a criterion of a stress ratio, 2.4 of US DOT-CFFC and Korean Standard, and indicated the safety. Thus, the optimized design elements based on the Taguchi's method were recommended as an aluminum liner thickness of 6.4mm, a carbon fiber laminate thickness in hoop direction of 31mm and a carbon fiber laminate thickness in helical direction of 10.2mm, which is represented by a design model of No. 5.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1994.06b
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• pp.59-65
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• 1994

본 논문에서는 Tichy와 Connor의 와전류 마그네틱 베어링 해석을 토대로 모의실험을 하여 주요 설계변수를 찾았고 반발식 마그네틱 베어링을 실제 제작하여 실험적으로 설계변수들이 마그네틱 베어링의 부하특성에 미치는 영향을 해석함으로써 설계 필요한 자료를 정립하였고 기존의 이론적 해석을 검증하였다.