Simulating delamination growth accounting for fracture directionality using a cohesive element approach

Abstract

Experiments have shown that the critical energy release rate (ERR) can vary as a function of the delamination in-plane propagation direction, relative to the bounding plies, and out-of-plane direction towards which it tends to grow, often referred to as delamination directionality. Despite the experimental evidence, delamination directionality is typically neglected in simulations. A cohesive element formulation is proposed that can simulate delamination growth while accounting for delamination directionality. The simulated fracture process is defined via piecewise-linear, independent, Mode I, II, and III traction separation laws (TSLs) and a directional mixed-mode fracture criterion. Mixed-mode loading conditions are simulated by scaling the pure mode TSLs based on the fracture criterion and the calculated mode-mixity. The same scaling concept is used in partially damaged material points to ensure that a change in fracture process (e.g. decrease/increase in critical ERR due to a variation in delamination directionality) is captured while preventing spurious delamination growth or healing and minimizing history dependence.