We consider the Robin Hood model of dry friction to study entropy transfer during sliding. For the polished surface (steady state) we study the probability distribution of slips and find an exponential behavior for all the physically relevant asperity interaction-distance thresholds. In addition, we characterize the time evolution of the sample by its spatial fractal dimension and by its entrop...

After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a c...

Friction between two objects can be understood by the making, stretching, and breaking of thousands of atomic-scale asperities. We have probed single atoms in a nonisotropic surface [the H-terminated Si(100) surface] with a lateral force microscope operating in noncontact mode. We show that these forces are measurably different, depending upon the direction. Experimentally, these differences ar...

In forming processes contact friction significantly influence metal flow, stress-strain state and process parameters. Furthermore, tribological conditions influence workpiece surface quality and its dimensional precision. This paper presents research results of the influence of contact friction coefficient on a workpiece surface quality in ring upsetting by flat plates. Workpiece surface roughn...

While its classical model is relatively simple, friction actually depends on both the interface properties of interacting surfaces and on the dynamics of the system containing them. At a microscopic level, the true contact area changes as the surfaces move relative to each other. Thus at a macroscopic level, total friction and normal forces are time-dependent phenomena. This paper introduces a ...

It is shown on the basis of scaling arguments that a disordered interface between two elastic solids will quite generally exhibit static and dry friction (i.e., kinetic friction which does not vanish as the sliding velocity approaches zero) because of Tomlinson-model instabilities that occur for small-length-scale asperities. This provides a possible explanation for why static and dry friction ...

This paper presents experimental measurements of the approach and rebound of a particle colliding obliquely with a wall in a viscous fluid. Steel and glass particles 12.7mm in diameter were used. The experiments were performed using a thick Zerodur wall (a glass-like material) with various mixtures of glycerol and water. Normal and tangential coefficients of restitution were defined from the ra...

We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally loaded polymer samples. The displacemen...

In this investigation three effects are included in a recently developed scale-dependent multi-asperity model of elastic contact and friction. First, a Weibull distribution of asperity heights is used, which allows the skew and kurtosis to be varied, but not independently of each other. Second, the effect of non-constant radii of curvature of the asperity summits, with the curvature varying wit...

Measurement of the coefficient of friction (COF) between the shoe/sole and the floor is essential in understanding the risk of slipping accidents. In this research, the COF of five floor materials commonly used on a university campus, under five surface conditions including dry and four liquid spillage conditions, were measured. The COF measurements were conducted using a Brungraber Mark II sli...