A strain energy-based parameter for predicting the crack initiation angle of mixed mode fracture

In this paper, a new parameter is developed for I-II mixed mode fracture analysis based on the concepts of the volume strain energy and deviator strain energy. For most fracture conditions, it has been demonstrated that the final fracture state is not dominated by the plastic deformation during the fracture process. For instance, mixed mode crack propagation occurs not along the direction of the maximum plastic deformation near the crack-tip. Based on this phenomenon, it is considered that the crack growth behavior is promoted by the volume strain energy, but not the deviator strain energy. Therefore, a new fracture parameter defined by the ratio (H-parameter) of the volume strain energy density to the deviator strain energy density is proposed for the investigation of crack growth behavior. It is assumed that the crack initiation angle can be determined by the direction of the maximum value of the H-parameter near the crack tip. This newly proposed H-parameter method is validated by comparison with classical criteria and experiments with two materials (PMMA and polysilicon) and shows a good accuracy.