Fatigue crack propagation normal to a plasticity mismatched bimaterial interface

Plasticity mismatched bimaterial specimens were made by explosive cladding with stainless steel and mild steel. Fatigue crack propagation normal to a bimetallic interface was experimentally investigated under a four-point bending condition. The results showed that material plasticity mismatch either promoted the crack growth as crack advanced to the interface from higher strength material side or retarded it as crack grew to the interface from lower strength material side. However, the cracks are always subjected to the interface shielding because of the interaction of the interface with the crack tip plastic zone for both cases above. For the present four-point bending specimens, the cracks can penetrate the next layer as the crack approaches the interface from either the higher or the lower yield strength side as long as the load levels are high enough. The effects of specimen geometry and dimensions on the fatigue crack deflection near to the interface are also discussed.