Toward efficient and robust computation of energy release rate and mode mix for delamination

Different methods for computing energy release rates for delamination are assessed with emphasis on their performance with large elements and irregular meshes. The jump in stress and strain that appears at the crack front with shell kinematics is used to compute the energy release rate in a simple manner via the jump in Eshelby tensor, without the mesh requirements that are associated with the virtual crack closure technique. The robustness of the results is examined for different kinematic formulations. For mode partitioning, another method that also makes use of the jump in stress [15], is modified for better performance with large elements. In this manner, the proposed method connects to existing concepts for characterization of fracture toughness based on linear elastic fracture mechanics. However, by presenting a size effect in the mode mix predicted with a cohesive method, it is emphasized that the validity of these concepts is questionable.