AN ANISOTROPIC MODEL OF DAMAGE AND FRICTIONAL SLIDING FOR BRITTLE MATERIALS

The paper provides important developments for the model of anisotropic damage by mesocrack growth, accounting for unilateral behaviour relat ive to crack closure (Dragon and Halm, 1996, Halm and Dragon, 1996). F rictional sliding of closed microcrack systems is introduced here as a n additional dissipative mechanism, which is considered to be coupled with the primary dissipative mechanism (damage by microcrack growth). Indeed, accounting for frictional sliding completes the description of moduli recovery in the existing model by adding to the normal moduli recovery effect (normal with respect to the crack plane) the substanti al recovery of shear moduli. In parallel to damage modelling, the inte rnal variable related to frictional sliding is a second-order tenser. Even if the unilateral effect and friction incipience are characterize d by a discontinuity of effective moduli, it is crucial to ensure cont inuity of the energy and stress-response. Relevant conditions are prop osed to ensure this. As far as frictional sliding is concerned, and un like most of the models based on the classical Coulomb law, the corres ponding criterion is given here in the space of thermodynamic forces r epresenting a form of energy release with respect to the sliding inter nal variable. It appears that the normality rule in the latter space f or sliding evolution is not physically contradictory with the observed phenomenon. The pertinence of the proposed theory, relative to the ma ximum dissipation hypothesis for both mechanisms, is illustrated by si mulating loading paths involving damage and friction effects. (C) Else vier, Paris.