The mechanics of interface fracture in layered composite materials: (2) cohesive interfaces

The author’s mixed-mode partition theories [1-9] for rigid interfaces are extended to non-rigid cohesive interfaces for one dimensional (1D) interface fracture. In the absence of crack tip through thickness shear forces both classical and shear deformable partition theories have identical mode I and II energy release rate (ERR) partitions which are the same as those of shear deformable partitions for a mixed mode at rigid interfaces and independent of interface cohesive laws. Consequently, the mode mixity remains constant during fracture evolution. In the case of interface fracture in the layered isotropic materials, the pure modes in 2D elasticity partition theory only depend on the ratio between the penalty stiffness to the Young’s modulus of the materials and are independent of the shape of the cohesive laws. A mixed fracture mode can be readily partitioned by using the pure modes and a constant mode mixity is shown.