NONLOCAL MODELS FOR DAMAGE AND FRACTURE - COMPARISON OF APPROACHES

The paper analyzes nonlocal constitutive models used in simulations of damage and fracture processes of quasibrittle materials. A number of nonlocal formulations found in the literature are classified according to the type of variable subjected to nonlocal averaging. Analytical a nd numerical solutions of a simple one-dimensional localization proble m are presented. It is shown that some of the formulations inevitably lead to residual stresses even at very late stages of the deformation process and, consequently, they are not capable of modeling complete s eparation in a widely open macroscopic crack. The mechanisms leading t o this specific type of stress locking are explained based on a theore tical analysis of the nonlocal constitutive equations. It is also poin ted out that the nonlocal approach distorts the shape of the stress-st rain diagram, which has to be taken into account when designing an app ropriate local softening law. (C) 1998 Elsevier Science Ltd. All right s reserved.