INTERACTIONS BETWEEN ADHESION AND FRICTION .1. THEORETICAL ASPECTS

The relationships between adhesion and friction are investigated, cons idering that there is a third thin layer separating the two sliding bo dies, submitted to continuous damage; both solids are supposed linearl y elastic, and the third body behaves as an elastoplastic damaged mate rial. From a thermodynamic framework, three-dimensional coupled elasto -plastic damage evolution equations are derived, The gradient of the d amage variable is introduced in the free energy of the intermediate la yer, so that the model accounts for the intrinsic cohesion of the laye r; nevertheless, it is assumed that the gradient is associated to a re versible behaviour. The three-dimensional friction model obtained is a pplicable to situations where the third body is either a polymeric or a metallic material. Using an asymptotic expansion method, a two-dimen sional model of the third body is then derived; the limit solution of the asymptotic expansion is such that the displacement field varies li nearly through the thickness of the layer-the stress field is constant -whereas the damage can vary. Assuming then that the damage is constan t through the intermediate layer, a two-dimensional constitutive law f or two bodies interacting through a thin third elastoplastic body is o btained, which accounts for adhesion effects. We lastly derive general ised friction laws including the effect of adhesion on friction, in wh ich the friction coefficient is a Function of a scalar adhesion variab le. Copyright (C) 1996 Elsevier Science Ltd.