• Composites Research
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• v.36 no.3
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• pp.141-153
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• 2023

This review paper presents an introduction of contact mechanics and rubber friction theory for sliding friction of elastomer composites in contact with rough surfaces. Particularly, Klüppel & Heinrich theory considers the self-affine (or fractal) characteristic for rough surfaces to predict adhesion and hysteresis frictions of elastomers based on the contact mechanics of Greenwood & Williamson. Due to dynamic excitation process of elastomer composites while sliding in contact with multiscale surface roughness (or asperity), viscoelastic properties in a wide frequency range becomes major contributor to friction behaviors. A brief description and examples are provided to construct a viscoelastic master curve considering nonlinear viscoelasticity of elastomer composites. Finally, application of rubber friction theory to tire tread compounds in traction with road surfaces is discussed with several experimental and theoretical results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1474-1486
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• 1990

The frictional characteristics of galvanized sheet steels(GA, EG, EGF, EGN) for automobiles were studied and compared with that of cold rolled sheet steel. A draw bead tester which simulates metal flow through a draw bead in stamping die face was used to measure coefficients of friction of galvanized sheet steels for four kinds of lubricants. Stamping formability of galvanized sheet steels for quarter outer panel was examined. The results show that stamping formability and friction characteristics were mainly influenced by the nature of zinc coating, surface roughness and micro hardness of coated layer, and proved to be very sensitive to the lubricant used.

• Tribology and Lubricants
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• v.25 no.1
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• pp.25-30
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• 2009

본 연구에서는 pin-on-disk 마찰 시험기를 통하여 Hexagonal 배열 $40{\mu}m$ Dimple 패턴의 효과를 실험하였다. 마찰 실험은 미끄럼 속도가 $0.06{\sim}0.34m/s$로 하였으며 마찰하중은 $20{\sim}100\;N$의 범위로 하였고, Dimple의 밀도는 $10{\sim}25%$의 범위로 제작하여 실험을 행하였다. 일반적으로 속도가 증가하고 하중이 감소할수록 마찰계수는 감소하는 경향을 나타내었으며, Dimple에 의한 마찰저감 효과는 속도가 $0.14{\sim}0.26m/s$의 범위에서 나타났다. $40{\mu}m$ Hexagonal 배열 Dimple 패턴의 마찰 특성에서는 밀도가 12.5%에서 가장 좋은 경향을 나타내었다.

• Tunnel and Underground Space
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• v.16 no.1 s.60
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• pp.58-72
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• 2006

In recent years, not only the occurrences but the magnitude of earthquakes in Korea are on an increasing trend and other sources of dynamic events including large-scale construction, operation of hi띤-speed railway and explosives blasting have been increasing. Besides, the probability of exposure fir rock joints to free faces gets higher as the scale of rock mass structures becomes larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, a shaking table test system was set up and a series of dynamic test was carried out to examine the dynamic frictional behavior of rock joints. In addition, a computer program was developed, which calculated the acceleration and deformation of the sliding block theoretically based on Newmark sliding block procedure. The static friction angle was back-calculated by measuring yield acceleration at the onset of slide. The dynamic friction angle was estimated by closely approximating the experimental results to the program-simulated responses. As a result of dynamic testing, the static friction angle at the onset of slide as well as the dynamic friction angle during sliding were estimated to be significantly lower than tilt angle. The difference between the tilt angle and the static friction angle was $4.5\~8.2^{\circ}$ and the difference between the tilt angle and the dynamic friction angle was $2.0\~7.5^{\circ}$. The decreasing trend was influenced by the magnitude of the base acceleration and inclination angle. A DEM program was used to simulate the shaking table test and the result well simulated the experimental behavior. Friction angles obtained by shaking table test were significantly lower than basic friction angle by direct shear test.

• Science of Emotion and Sensibility
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• v.7 no.4
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• pp.25-33
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• 2004

This study surveys the fabric surface properties such as mean value of the friction coefficient(MIU), mean deviation of the friction coefficient(MMD) and mean deviation of surface roughness(SMD) due to warp and weft tension differences using KES-FB system. For this purpose, fabric is designed as 5 harness Satin weave using 75d/36f warp and 100d/192f weft polyester filaments, and is woven by OmegaR rapier loom by Textec Co.Ltd and Picanol-GTXR rapier loom by Picanol Co.Ltd respectively. These grey fabrics are processed on the same dyeing and finishing processes. The fabric surface properties according to the weaving looms are analysed with warp and weft weaving tensions. And also surveyed the difference of fabric surface properties according to the fabric positions such as center and each edge of fabrics for the sensitive garment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.5
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• pp.439-445
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• 2005

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as seal rings, pump parts, meter parts, and so on. In this study, the effects of each other purity on the mechanical and tribological properties of alumina and zirconia ceramics were investigated. Sliding distance, sliding speed, contact load. friction coefficient, the amount of worn out material at a certain time, and the prepared composites were measured. Crystalline phases and microstructure were examined with XRD and SEM. We obtained the good properties of friction coefficient and wear resistance at the purity 99.7$\%$ of alumina. However, The purity 95$\%$ were great at the wear amount of worn out material.

• Resources Recycling
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• v.11 no.3
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• pp.37-45
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• 2002

Triboelectrostatic Separation procese is a technology that different particles charged after contact and rubbing different materials are separated in an electric field. At this time, charged polarity of different materials depends on their own work function. Therefore this study discovers work functions of various plastics and determines charging characteristics for the specific optimum operation condition. The experiment is conducted with two sample sets composed of various different plastics. Each sample is charged by contact and rubbing different materials. Surface charge of charged particles is measured by Faraday Cage. The specific work function of an each plastic is driven by measured charging amount and charged particles are separated in a certain electric field ($\pm$20 kV). At last, the relationship between charging amount and separation efficiency is induced by the separation experiment.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.166-178
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• 2006

Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.703-703
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• 2013

다이아몬드상 탄소 박막(Diamond-like carbon, DLC) 박막은 낮은 마찰 계수, 높은 내마모성, 화학적 안정성, 적외선 영역에서의 높은 투과율 등의 장점을 바탕으로 MEMS (Micro-Electro Mechanical System) 소자와 MMAs (Moving Mechanical Assemblies)의 고체윤활코팅, 마그네틱 미디어와 하드디스크의 슬라이딩 표면 등 다양한 분야에 코팅소재로써 응용되어왔다 [1,2]. 현재 전기철도용 집전판은 마찰이 적고 전도성을 지니는 카본 소재로 구성되어 있다. 그러나 그 마모 비율이 너무 심하여 이를 개선할 수 있는 방안으로 고경도 저마찰력을 지니는 DLC 박막을 코팅 소재로써 제안하고자 한다. 그러나 기존에 DLC 박막은 절연특성이 매우 우수하기 때문에 기존에 전도성을 지니는 카본 집전판에 적용하기에는 어려움이 따른다. 따라서 DLC 박막 내에 실리콘(Si) 또는 금속(Metal)을 첨가시키거나, 금속 중간층을 포함시켜 전기적으로 전도특성을 향상시키는 방안이 제시되고 있으며, 본 연구에서는 DLC 박막과 유사하게 우수한 경도특성을 지니고, 낮은 마찰계수등을 지니는 비정질 탄소박막을 연구하여 카본 집전판에 코팅하고자하며, 특히 비정질 탄소박막에 금속 Ti를 도핑하여 집전판과의 접착력과 전기적 전도 특성을 향상시키고자 한다. Ti가 도핑된 탄소박막(TiC) 박막은 비대칭 마그네트론 스퍼터링(unbalanced magnetron sputtering; UBMS) 시스템을 이용하여 제작하였으며, 스퍼터링 조건 중 기판에 인가되어지는 기판온도에 따라 변화되어지는 TiC 박막의 트라이볼로지(Tribology) 특성을 고찰하고자 하였다. 증착시 기판온도의 증가는 TiC 박막의 경도, 마찰계수 특성등 트라이볼로지 특성을 향상시켰으며, 전기적 전도 특성을 향상시켰다. 이러한 결과는 스퍼터링 방법에 의해 증착되어진 TiC 박막내에 존재하는 sp2 결합과 관계가 있음을 확인할 수 있으며, 트라이 볼로지 특성은 TiC 박막내에 sp2 탄소결합의 비율 증가와 관련되어졌다. 특히 sp2 탄소결합은 TiC 박막 증착시 증가된 기판온도와 밀접한 관계가 있으며 기판온도의 증가에 따라 나노결정 클러스터의 크기와 수의 변화와 밀접한 관계가 있음을 확인하였다. 결국 기판온도는 TiC 박막의 트라이볼로지 특성을 향상시켰으며, 전기적 특성 또한 향상시켜 전기철도 집전판에 응용을 위한 소재로 평가할 수 있다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.124-124
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• 2012

접촉운동기구 계면에서의 마찰력은 요소 혹은 시스템의 효율과 직접적으로 연관이 있으며 이로 해 마찰계수를 낮추기 위한 저마찰 표면처리는 Tribology 연구에 있어 기초적이면서도 동시에 매우 중요한 부분으로 오래 전부터 인식되어오고 있다. 또한 대부분의 습동기구 표면이 경화 처리되어 마모에 강한 특성을 보이나 이는 마찰계수가 일정 이하로 낮게 유지될 경우에만 해당되는 것으로 마찰계수의 조절은 매우 중요하다고 할 수 있다. 과거 자동차 엔진의 실린더 라이너 표면에 가공된 사선 형태의 패턴들이 저마찰 기능을 하는 것은 이미 잘 알려진 사실이며 최근에는 이러한 패턴 혹은 형상을 인위적으로 조절하여 저마찰 기능과 성능을 더욱 높이고자 하는 연구가 활발히 진행되고 있다. 이와 같은 미세한 패턴은 다양한 가공기술의 발전에 의해 가능하게 되었으며 그 결과 마찰계수는 패턴의 형상과 분포 등과 매우 밀접한 관계가 있는 것으로 보고되어 있다. 본 연구에서는 최근 활발한 연구가 진행되고 있는 표면 텍스쳐링 분야에 대한 전반적인 연구 동향과 미래의 가능성에 대해 살펴보고자 한다.