Fatigue Crack Initiation and Growth in a High-Strength Ductile Steel Subject to In-Plane Biaxial Loading
SourceFlat cruciform-shaped specimens of HY100 steel were tested in fatigue under biaxial stress states. For Mode I crack growth, a tensile component of stress parallel to the crack decreased crack growth rate; a compressive component had the opposite effect. These changes in growth rate are explained in terms of the material's differing cyclic stress-strain response under shear and equibiaxial loading.
Studies of Mode II growth were found difficult to perform, due to a critical balance between Mode II and Mode I growth. Mode II crack growth rates were much greater than for the equivalent Mode I crack. The growth rate increased with increasing ΔKII but did not follow the Paris relationship due to the occurrence of incipient or undeveloped bifurcation which prevented continued and undisturbed Mode II growth.