Fatigue crack propagation behavior in the vicinity of an interface betweenmaterials with different yield stresses

The problem of a fatigue crack approaching an interface in a bi-material an d an interlayer is experimentally investigated. Cracks propagating perpendi cular to the sharp ferritic steel - ferritic steel interface are studied. T he elastic and thermal expansion properties are nearly identical, only the plastic properties are different. The previously reported, theoretically pr edicted slowdown of the growth rate in the case of a weak/strong transition and the acceleration in the case of a strong/soft transition are verified. Two surprising results are: the bifurcation of the crack in the vicinity o f the interface when the crack propagates from the weak to the strong mater ial, and the relatively large effect of the extremely small thermal mismatc h on the crack propagation behavior. (C) 2000 Elsevier Science S.A. All rig hts reserved.