AbstractFatigue-crack propagation in biaxially stressed plates has been investigated. The normal stress σx, applied on a plane perpendicular to the crack front, affects the rate of propagation of a Stage II crack extending by a Mode I mechanism. This stress, which does not affect singularity conditions in a linear elastic fracture mechanics analysis, has different effects should it be tensile or compressive, cyclic or constant. The changes in crack-growth rate are related to changes in the size of the plastic shear ears at the tip of the crack. Fatigue-crack propagation is related to two parameters in the plane of the plate, the maximum shear stress range and the stress normal to the plane of maximum shear. Both these parameters will affect the crack-opening displacement and hence crack-growth rate.
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