Dry Friction as an Elasto-Plastic Response: Effect of Compressive Plasticity

Unlike the well known Amontons-Coulomb laws of dry friction, the recent precise experimental studies of low velocity friction dynamics provide sensitive tests for a theoretical description. We introduce a model, in which the friction force originates from multistability induced by interactions of individual pairs of asperities whose properties undergo a slow time evolution due to plastic creep induced by the compressive 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. Instability with respect to the onset of stick slip is found, but open questions remain concerning the features of the corresponding bifurcation, pointing towards the need to extend the model to take into account shear-induced plastic effects.