Strain-softening in continuum damage models: Investigation of MAT_058

Composite materials are of increasing interest to automotive and aviation industry due to their high strength and stiffness. Therefore they are commonly used to replace metallic materials. However their mechanical behaviour is complex, especially when damage is considered. Composite damage leads to degradation of material properties which results in behaviour known as strain-softening. ® An implementation of strain-softening in numerical codes, such as LS-DYNA , leads to mesh sensitivity of results and therefore those models are not reliable. The user of damage models with strain-softening needs a good understanding of those material models to evaluate results critically. This work aims to provide an insight on strain-softening behaviour in a mathematical sense and its consequences on numerical codes. An analytical solution is derived for a one-dimensional dynamic bar problem which allows a direct comparison with numerical results. It was found that deformation localises in an area which is governed by the chosen element size and therefore causes mesh sensitivity. Strain grows infinitely in the strain-softening area with a simultaneous drop of stress. Outside the strain-softening area the problem unloads elastically. The dissipated energy tends to vanish.