• Coupled systems mechanics
• /
• 제7권5호
• /
• pp.583-610
• /
• 2018

This paper discusses the issues associated with modeling frictional contact between solid bodies undergoing large deformations. The most common model for friction on contact interfaces in solid mechanics is the Coulomb friction model, in which two distinct responses are possible: stick and slip. Handling the transition between these two phases computationally has been a source of algorithmic instability, lack of convergence and non-unique solutions, particularly in the presence of large deformations. Most computational models for frictional contact have used penalty or updated Lagrangian approaches to enforce frictional contact conditions. These two approaches, however, present some computational challenges due to conditioning issues in penalty-type implementations and the iterative nature of the updated Lagrangian formulation, which, particularly in large simulations, may lead to relatively slow convergence. Alternatively, a plasticity-inspired implementation of frictional contact has been shown to handle the stick-slip conditions in a local, algorithmically efficient manner that substantially reduces computational cost and successfully avoids the issues of instability and lack of convergence often reported with other methods (Laursen and Simo 1993). The formulation of this approach, however, has been limited to the small deformations realm, a fact that severely limited its application to contact problems where large deformations are expected. In this paper, we present an algorithmically consistent formulation of this method that preserves its key advantages, while extending its application to the realm of large-deformation contact problems. We show that the method produces results similar to the augmented Lagrangian formulation at a reduced computational cost.

• Tribology and Lubricants
• /
• 제25권2호
• /
• pp.81-85
• /
• 2009

Interests in micro/nano-particles have been greatly increasing due to their wide applications in various fields such as environmental and medical sciences as well as engineering. In order to obtain a fundamental understanding of the tribological characteristics at particle-surface contact interface, frictional behaviors according to load/pressure and materials were obtained by using atomic force microscope(AFM) cantilevers with different stiffnesses and tips. Lateral contact stiffnesses were observed in various tip-surface contact situations. Experimental results show that stick-slip friction behavior occurs even when the colloidal probes with a particle of a few micrometers in diameter, which have a relatively large contact area and lack a well-shaped apex, were used. This indicates that atomic stick-slip friction may be a more common phenomenon than it is currently thought to be. Also, experimental results were investigated by considering the competition between the stiffness of the interatomic potential across the interface and the elastic stiffnesses of the contacting materials and the force sensor itself.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.61-62
• /
• 2002

In order to clarify the contact mechanism between specimen surface and probe tip in the surface observation by the AFM (atomic force microscope) or the FFM (friction force microscope), several molecular dynamics simulations have been performed. In the simulation, a 3-dimensional simulation model is proposed where the specimen and the probe are assumed to consist of mono-crystal line copper and a carbon atom respectively and the effect of cantilever stiffness is also taken into considered. The surface observation process on a well-defined Cu{100} is simulated. The influences of cantilever stiffness on the reactive force images and the behavior of probe tip were evaluated. As a resuIt, several phenomena similar to those observed by the actual surface observation experiment, such as double-slip behavior and dispersion in the stick-slip wave period were observed.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
• /
• pp.643-648
• /
• 2011

Fatigue crack in most rails take place by rolling contact between wheel and rail in railway industry. Therefore, it is critical to understand the rolling contact phenomena, especially for the three-dimensional situation. In this paper the steady-state rolling contact problem of KTX wheel and rail (UIC60) has been studied with three-dimensional finite element analysis. The variation of contact pressure and contact stresses on rolling contact surface were obtained using the finite element method. The three-dimensional distribution of contact stresses on the contact surface are investigated. Results show that the distribution of shear stress and contact stress (von Mises) on the contact surface varies rapidly as a result of the variation of stick-slip region. The contact stress at the leading edge is greater than at the trailing edge because of stick and slip phenomena.

• 소음진동
• /
• 제11권3호
• /
• pp.461-470
• /
• 2001

A friction-type clutch system sometimes generates spick-slip vibration during engagement, which disturbs smooth start of a car and makes a passenger uncomfortable. In this study, the spick-slip vibration in four types of friction couples was investigated at two different engagement conditions respectively of which the amount of slip time and clutch travel was varied. Results are found as follows. First, the vibration increased at the condition of small engine torque and large torque fluctuations due to higher harmonics of engine speed. Second, the friction couple without a pre-damper has advantages of reducing the vibration. This study also suggested an evaluation method of vehicle vibration in the view point of human perception by using the frequency weighting of ISO2631-1.

• 한국표면공학회지
• /
• 제8권2호
• /
• pp.20-27
• /
• 1975

• Tribology and Lubricants
• /
• 제16권4호
• /
• pp.302-307
• /
• 2000

The fretting wear characteristics of STS304 steel in seawater were investigated experimentally. A fretting wear tester was designed to be suitable for this fretting test. This study was focused on the effects due to the combination of normal load, slip amplitude and number of cycles and corrosive environment as the main factors of fretting. The results of this study showed that the wear volume increased abruptly at slip amplitude between 70 $\mu\textrm{m}$∼100 $\mu\textrm{m}$ by fracture of oxide layers but above that slip amplitude the wear volume increased steadily.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1996년도 제24회 춘계학술대회
• /
• pp.25-29
• /
• 1996

The fretting wear characteristics for Zircaloy-4 tube used as fuel rod in the nuclear power plant have been investigated. The fretting wear tester was designed and manufactured for this experiment. This study was focused on main factors of fretting wear, cycle, slip amplitude and normal load. The worn surfaces were observed by SEM.

• 지질공학
• /
• 제19권3호
• /
• pp.277-285
• /
• 2009

단층슬립의 기하분석에 의한 단층의 거동특성을 평가하고자 주단층의 주향변화, 단층 선단부의 발달 상태, 단층대의 폭의 주기적 변화, 단층암의 변형양상, 2차 소단층의 각관계를 근거로 양산단층의 주향을 따라 남쪽 양산에서 북쪽으로 포항시 신광면에 이르는 구간을 5개의 구역($A{\sim}E$)으로 구분하였다. 또한 가상의 단층비지를 대상으로 시행한 이전 여러 실험연구 결과들로부터 얻어진 단층작용의 운동 양상과 변형 조직과의 관계를 양산단층에 적용하고자 하였다. 단층의 미끄럼 거동을 이해하기 위하여 양산단층을 따라 단층의 자세와 단층슬립을 측정하였고, 주단층과 2차 소단층의 Riedel shear 각 관계를 분석하였다. 양산단층 각 구역에서 주단층과 2차 단열의 방향성 및 단층슬립을 이용하여 각 구역별 단층의 거동특성을 해석한 결과 A, D 및 E와 같은 직선구역들은 안정된 전단운동을 한 creeping 운동의 구역으로 평가되었고, 반대로 B와 같은 곡선구역은 stick-slip 운동을 한 locked 구역으로 평가되었다.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2002년도 춘계학술대회 논문집
• /
• pp.528-535
• /
• 2002

In order to achieve high precision machine tools, the research for performance enhancement of feed drive systems is required. Development of the high speed feed drive system has been a major issue for the past few decades in machine tool industries. The reduction of the tool change time as well as rapid travel time can enhance the productivity. However, the high speed feed drive system generates more heat in nature, which leads thermal expansion that has adverse effects on the accuracy of machined parts. Stick-slip friction has a great influence on the contouring accuracy of CNC machine tools. In this paper table levitation system has been developed for the stick-slip in a feed drive systems. And also, the driving position is set near the center of the main slideway. From the results, it is confirmed that yaw error and straightness can be improved.