4271 - REGULARIZED DAMAGE MODEL BASED ON NONLOCAL DISPLACEMENT FIELD

Continuum damage models describe the changes of material stiffness and strength, caused by the evolution of defects, in the framework of continuum mechanics. In many materials, a fast evolution of defects leads to stressstrain laws with softening, which creates serious mathematical and numerical problems. To regularize the model behavior, various generalized continuum theories have been proposed. Integral-type nonlocal damage models are usually based on weighted spatial averaging of a strain-like quantity. This paper explores an alternative formulation with averaging of the displacement field. It is shown that an exact equivalence between strain and displacement averaging can be achieved only in an unbounded medium. Around physical boundaries of the analyzed body, both formulations differ and the nonlocal displacement model generates spurious damage in the boundary layers. The paper shows that this undesirable effect can be surpressed by an appropriate adjustment of the nonlocal weight function. The first numerical tests indicate that, in terms of global characteristics such as the load-displacement curves, the results obtained with the newly proposed formulation are very similar to those obtained with the usual formulation based on strain averaging, but locally they give a smoother distribution of stress and surpress oscillations observed for the usual formulation in certain regions of the process zone.