Phase-field modeling of crack propagation in layered materials with weak interfaces

We study crack propagation in layered materials with weak interfaces under purely mechanical loading, using a hybrid phase-field method that is implemented in deal.II, an open source finite element library. Interface weakening is incorporated in the hybrid phase-field model by modifying the total energy of the system with the interface energy contributions which are evaluated as an additional surface integral at material interfaces. First, we validate our implementation by comparing our results against existing literature on a benchmark 3D fracture problem where crack twisting is observed. We then demonstrate the framework’s ability to model fracturing in a bilayered material with a weak material interface. In this example, crack nucleation is observed at the weak interface directly below the point of maximum applied displacement and subsequent propagation occurs along the weak interface causing partial debonding of the two layers. As expected, with decreasing interface strength, the peak load also decreases validating the proposed model of interface weakening in phase-field fracture framework. Finally, we present two examples demonstrating fracturing in a multilayered material with several weak interfaces. First, we study the combined effect of stiffness mismatch and interface strength on crack propagation in layered materials. Our results show that stiffness mismatch does not dictate crack deflection along the interface. Crack deflection or penetration at the interface is solely controlled by interface strength. In the final example we see that even if the bulk material is homogeneous, crack deflection along layer interfaces is possible if the interface strength is low. Penetration dominates for strong interfaces with the effective strength more than fifty percent of their original strength, while delamination is preferred for weaker interfaces with effective strength lower than fifty percent of their original strength.