A kinking-based failure model for engineering simulation of compressive crushing of composite structures

The use of continuum damage models is state of the art for the finite element modelling of progressive damage and failure under compressive loading in composites during e.g. crash and impact simulations. However, after failure initiation the compressive stress is quickly degraded to zero alternatively to a plateau with constant stress and at a certain point the element needs to be deleted due to the damage level or large element deformation. This effectively represent a void in the material which contrasts with reality where a fully formed kink band would be expected to have compressive properties similar to the transverse direction of the ply. To better represent this physical behaviour is here a kinking formulation developed that instead of the common constant stress plateau after initial softening features a stiffening at larger strains. This formulation has been implemented in a commercial FE-code complemented by criteria for kinking initiation and kink band broadening. The results presented show the novelty of the model in that it describes a chain of events starting with initiation of kinking, progressing to the growth of kink bands through the element and finally including an increase in stress that initiate kinking in adjacent elements.