• Tribology and Lubricants
• /
• 제38권5호
• /
• pp.199-204
• /
• 2022

This paper presents a numerical investigation of the influence of water molecule thickness on frictional behavior at the nanoscale using molecular dynamics simulation. Three different models, comprising water thin films of various thicknesses, were built, and indentation and sliding simulations were performed using the models. Various normal loads were applied by indenting the Si tip on the water film for the sliding simulation to evaluate the interplay between the water thin film thickness and the normal load. The results of the simulations showed that the friction force generally increased with respect to the normal load and thickness of the water thin film. The friction coefficient varied with respect to the normal load and the water film thickness. The friction coefficient was the smallest under a moderate normal force and increased with decreasing or increasing normal loads. As the water film became thicker, the contact area between the tip and water film became larger. Under well-lubricated conditions, the friction force was proportional to the contact area regardless of the water film thickness. As the normal force increased above a critical condition, the water molecules beneath the Si tip spread out; thus, the film could not provide lubrication. Consequently, the substrate was permanently deformed by direct contact with the Si tip, while the friction force and friction coefficient significantly increased. The results suggest that a thin water film can effectively reduce friction under relatively low normal load and contact pressure conditions. In addition, the contact area between the contacting surfaces dominates the friction force.

• 한국자동차공학회논문집
• /
• 제12권2호
• /
• pp.160-167
• /
• 2004

A two degree-of-freedom mathematical model is presented to investigate the friction mechanism of a disc brake system. A contact parameter is introduced to describe the coupling between the in-plane and the out-of-plane motions. The model with the contact parameter is considered under the assumption that the out-of-plane motion depends on the friction force along the in-plane motion. In order to describe the relationship between the friction force and the out-of plane motion, the dynamic friction coefficient is considered as a function of both relative velocity and normal farce. Using this friction law, a contact stiffness matrix along the normal direction can be obtained. The out-of-plane motion is then investigated by both the stability analysis and the numerical analysis for various parametric conditions. The results show that the stiffness parameters of the pad and the disc must be controlled at the same time. Also, the numerical analysis shows the existence of limit cycle caused by the effect of intermittent contact stiffness.

• Structural Engineering and Mechanics
• /
• 제4권3호
• /
• pp.257-276
• /
• 1996

In North America, a large number of concrete old slab-on-steel girder bridges, classified noncomposite, were built without any mechanic connections. The stablizing effect due to slab/girder interface contact and friction on the steel girders was totally neglected in practice. Experimental results indicate that this effect can lead to a significant underestimation of the load-carrying capacity of these bridges. In this paper, the two major components-concrete slab and steel girders, are treat as two deformable bodies in contact. A finite element procedure with considering the effect of friction and contact for the analysis of concrete slab-on-steel girder bridges is presented. The interface friction phenomenon and finite element formulation are described using an updated configuration under large deformations to account for the influence of any possible kinematic motions on the interface boundary conditions. The constitutive model for frictional contact are considered as slip work-dependent to account for the irreversible nature of friction forces and degradation of interface shear resistance. The proposed procedure is further validated by experimental bridge models.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.1262-1265
• /
• 2004

A cycloidal speed reducer is a type of the speed reducers of machinery. The cycloidal speed reducer consists of two cycloidal plate gears, housing roller gear, input shaft, output pin and shaft, and eccentric bearings. Especially the cycloidal plate gear has the peculiar parts of the teeth, because of gearing with the housing roller gear that has the several rollers on the circular line. And then all teeth on the cycloidal plate gear can be designed to contact with the rollers on the housing roller gear at the same time. Therefore the cycloidal plate gear has always contact motion with rollers and the force is interacted between roller gear with cycloidal plate gear. Because the contact force and friction force must be required to improve the accuracy in design procedures of cycloidal speed reducers, this paper presents a force analysis considered friction effect approach derived by static force equilibrium condition, geometrical adaptation, instant velocity center method and relative velocity method.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1999년도 제30회 추계학술대회
• /
• pp.193-199
• /
• 1999

In the 3-Dimensional contact of the smooth spheres, the effects of friction on the contact area and the distribution of contact pressure was studied numerically. The contact area and pressure distribution was evaluated for the only normal load and for the case of a normal load in the presence of a tangential traction. To do this work, the technique of simple discretization using the load . displacement relationship for a uniformly distributed load of a rectangular patch was used.

• 한국철도학회논문집
• /
• 제17권1호
• /
• pp.14-18
• /
• 2014

차륜/레일 접촉은 철도차량의 동특성을 결정하는 중요한 요소이다. 본 연구에서는 철도 차륜과 레일 사이에 작용하는 토크에 의한 견인력과 마찰력을 두 원통의 접촉문제로 이론해석과 전산해석을 하고 수직하중과 전단력이 작용하는 실제 차륜과 레일에 대한 전산해석을 하였다. 철도차륜과 레일 접촉문제는 구름과 미끄러짐이 있는 탄성접촉인 크리프에 의한 크리프힘을 생성하는 과정으로서 차륜과 레일의 형상 및 마찰계수에 따라 달라짐을 알 수 있었다.

• 소성∙가공
• /
• 제24권6호
• /
• pp.381-386
• /
• 2015

Recently, high-strength-steel sheets have been used extensively for increasing fuel-efficiency and stability in automobiles. A study on the characteristics regarding friction factors is required because high-strength-steel sheets have higher contact pressure at the tool interface as compared to low-strength steel sheets. For the current study, a sheet friction test was used to examine the influence of several factors on friction. The friction tests were performed on two types of sheet steels (SPFC590 and SPFC980) to obtain friction coefficients as a function of contact pressure, surface roughness, lubricant viscosity, and speed. Based on the experimental results for SPFC590 and SPFC980, the friction coefficient decreased with increasing contact pressure, but the friction coefficient increased with increasing surface roughness. Also, the friction coefficient decreased with increasing lubricant viscosity and decreasing speed.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.385-386
• /
• 2002

The friction characteristics of contact region between vane tip and cam-ring is studied with an experimental device model. The radius of vane tip is less than 1 mm and sliding speed is lower than 10 m/s. The friction characteristics of the actual oil hydraulic vane pump is estimated on the basis of coefficient of friction. The coefficient of friction can be obtained by measuring the frictional forces in the contact region. The lubrication condition between vane and disk is modeled after the actual condition between the vane and cam-ring.

• Tribology and Lubricants
• /
• 제20권5호
• /
• pp.266-271
• /
• 2004

The aim of this paper is to investigate the effect of surface texturing on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.217-222
• /
• 2004

The aim of this paper is to investigate the effect of micro-dimple size on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.