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

The problem of a fatigue crack approaching an interface in a bi-material and an interlayer is experimentally investigated. Cracks propagating perpendicular to the sharp ferritic steel – ferritic steel interface are studied. The elastic and thermal expansion properties are nearly identical, only the plastic properties are different. The previously reported, theoretically predicted 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 of the interface when the crack propagates from the weak to the strong material, and the relatively large effect of the extremely small thermal mismatch on the crack propagation behavior.