Sliding as Jogging and Contact Waves

Abstract

As can be derived from non-equilibrium thermodynamics [3, 4], the dissipation of energy increases entropy. This means that the mechanical scheme of sliding with constant speed along smooth solids contradicts to the thermodynamics. If there is an interaction, the constant speed sliding is impossible. If there is no interaction, the increase entropy does not occur, i.e. there is no friction. Thus, for the problem of friction it is very important to consider the non-
equilibrium form of movement. This non-equilibrium motion is principally related to instability.
On the atomic scale level Tomlinson [2], described a possible mechanism for the energy loss in friction by assuming a non-adiabatic change in positions of atoms involving phononic, or lattice vibration mechanisms. He was the first to point out the importance of the non-adiabatic motion. There are many possible origins of elastic instabilities, e.g., they may involve individual molecules or groups of molecules, groups of asperities, gripped places on macro-profile. As a result the overall motion may not exhibit any stick and slip behavior at macroscopic level, since the local rearrangements can occur at different times in an incoherent manner or more likely contrary forming a dissipation structures [4, 5]. Coming from B. Mandelbrot fractal ideas [3] it is easy to realize that frictional sliding is complicated fractal movement including multi-scale instability.

The interfacial sliding is a complicated fractal movement including multi-scale wave patterns. The contact wave is dislocation-like release movement along contact surface at high, sound level, phase speed. Single asperity involves in running contact cluster at the front edge and in short time at the back edge of the cluster it gain normal and tangential jump so mean speed equals to the macro-sliding speed but the mean speed on hard contact places droop considerably. Normal and tangential load increase proportional to wave phase rate. It possible to consider sliding waves on macro micro and nano scale levels.

Figure1. Scheme of contact wave.

Draft

References

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