Fatigue crack growth at arbitrary angles to bimaterial interfaces

Abstract

The fracture characteristics of monotonically loaded cracks located parallel to, in the vicinity of, and at arbitrary angles to the interface between two elastic solids have the subjects of considerable theoretical research in the literature. The present experimental work on steel-steel bimaterials clearly demonstrates that, for essentially the same elastic properties, the plastic mismatch between the constituent layers of bilayer composite can dictate whether a fatigue crack approaching the interface at various angles continues to advance through the interface or arrests prior to penetrating the interface. The former crack arrest phenomenon occurs when the fatigue crack approaches the interface from the plastically weaker material, whereas continued crack growth results when the crack approaches the interface from the plastically stronger material. The observed experimental trends are qualitatively consistent with the numerical predictions of crack-tip shielding or amplification from the interaction of the near-tip plastic zone with an interface oriented normal to the plane of the crack. When the fatigue crack is initiated parallel to the interface, it deviates from the strongly bonded interface to advance in one of the two steels. This trend appears to experimentally confirm predictions of the possible evolution of strong mode mixity ahead of interface cracks subjectedmore » to cyclic tensile loading.« less