Influence of sliding contact local dynamics on macroscopic friction coefficient variation

Abstract : The aim of this paper is to present a means of analysing "friction instabilities". The explicit dynamic finite element software PLAST3 in 3D is used to simulate the behaviour of the two bodies (pin and disk) of a tribometer during frictional contact. Coulomb's friction law is used at the contact surface. The phenomenon of relay between the instantaneous contact zone, the contact stresses distribution and the kinematics of the contact surfaces are presented. As the friction coefficient and velocity of the disk are considered constants in the simulations, the contact zone (stick, slip) and separation depend on a "dynamic effect". This generates wave propagation in the interface and involves a variation of normal contact stress. Definitions of macroscopic and local friction coefficients are given. The interfacial instabilities due to the dynamic effect produce a macroscopic friction coefficient that is less than the local friction coefficient. The influence of disk velocity on the macroscopic friction coefficient is also investigated.