Propagation behavior of fatigue crack normal to the interface of bimetallic laminates with plasticity mismatch

Propagation behavior of fatigue crack perpendicular to the bimetallic laminates interface was experimentally investigated under four points bending condition. The laminates are composed of the materials with same elastic modulus and different yield strengths. It is generally demonstrated that the material mismatch in yield strength either promotes the crack growth as crack advances to the interface from higher strength material side or retards it as crack grows to the interface from lower strength material side. The crack, however, is always subjected to the interface shielding for both cases above, whereas the dominated range depends on the material side from which the crack starts to propagate. The crack could penetrate into the next, layer by passing through the interface whatever crack approaches to the interface from either the high or low yield strength side as long as the load is high enough. The effect of specimen geometry and the related tau stress on crack growth near to the interface is also discussed.