Simulation of local instabilities during crack propagation in the ductile–brittle transition region

The crack propagation for a cohesive zone model within an elastic-plastic material under small-scale yielding conditions is simulated numerically. The resulting crack growth resistance curves show local instabilities, so-called pop-ins even for homogeneous cohesive properties if the cohesive strength lies sufficiently close to the maximum stress of the corresponding blunting solution. The formation of secondary cracks and unloading zones in front of the actual crack tip is identified as the underlying mechanism. It is found that the shape of the cohesive law has a considerable influence on the crack arrest behavior. Furthermore, requirements to the mesh resolution are derived.