Interaction of Dynamic Cracks with Inclined Interfaces

Catastrophic failure of any brittle structure under dynamic loading consists of dynamic crack initiation, propagation, curving, branching (both micro and macro) and branching instability. However, the failure is much more complex in case of layered materials which has interfaces. In these materials, other than above crack mechanisms the crack can also deflect to propagate along the interface or penetrate through the interface when it reaches the interface. In order to understand these features, a detailed experimental investigation is essential. Simple specimen configurations have been designed to look into these features both qualitatively and quantitatively. Dynamic photoelasticity coupled with high-speed photography is used to capture real-time crack propagation. An initial experimental study has already been conducted to identify important parameters that affect the penetration and deflection behavior. It has been observed that incoming crack tip velocity and mode mixity have influence on the nature of crack propagation along the interface. To validate these observations, an extensive set of well controlled experiments will be conducted. In parallel to these experiments, a series of large scale simulations using cohesive zone interfacial elements will be performed. The above mentioned specimen configurations are well designed to have very simple boundary condition. The specimen is wedge loaded dynamically so that other edges of the specimen are stress free. To perform these simulations, two set of inputs are necessary. The first one is to provide valid loading boundary conditions and the second one is to incorporate accurate cohesive zone laws in the dynamic fracture of the simulated specimen. To meet the first input, a modified Hopkinson bar setup has been used to accurately control initial and boundary conditions. In case of second input, an inverse formulation approach will be used to extract cohesive zone laws for both mode-I and mixed mode conditions.