Wear phenomena due to contact and relative motion between two solids depend on the loading conditions and material mechanical behaviours and are charaterized by a loss of materials. Particles are detached from sound solids when some criteria are satisfied at the boundaries of the solids along the contact area. The evolution of the damaged surface is investigated in a thermomechanical analysis. This framework proposes a definition of mechanical local quantities, which can be usefull for the characterisation of wear process. Interface behaviour is analyzed.