DRY FRICTION AS AN ELASTOPLASTIC RESPONSE - EFFECT OF COMPRESSIVE PLASTICITY

Unlike the well known Amontons-Coulomb laws of dry friction, the recen t precise experimental studies of low velocity friction dynamics provi de sensitive tests for a theoretical description. We introduce a model , in which the friction force originates from multistability induced b y interactions of individual pairs of asperities whose properties unde rgo a slow time evolution due to plastic creep induced by the compress ive forces acting on the real contacts. Even a crudely schematic form of the model reproduces the time strengthening of the static friction force and the velocity weakening of the steady motion dynamic one. Ins tability with respect to the onset of stick slip is found, but open qu estions remain concerning the features of the corresponding bifurcatio n, pointing towards the need to extend the model to take into account shear-induced plastic effects.