Bimaterial interfacial crack growth with strain gradient theory

The purpose of this paper is to investigate the ejfect of material heterogeneity on damage evolution and subsequent crack propagation in bimaterial systems. Strain gradient theory analysis reveals that a higher stress triaxiality always occurs on the softer material side due to the material mismatch in yield capacity and the corresponding strain gradient along the interface. High stress triaxiality is a major condition which promotes ductile damage and facilitates crack growth. To investigate this link, numerical simulations of ductile interface crack growth are performed using a damage based constitutive model. Both the numerical and experimental results show that a crack may grow along the interface or deviate into the softer material, but never turn into the harder material. The theoretical and numerical analysis reveal three factors which strongly affect the direction of crack growth and the resistance capacity of the bimaterial system against fracture. These are the boundary conditions which determine the global kinematically admissible displacement field, the stress/strain gradient near the interface due to the material mismatch, and the distance from the crack tip to the interface.