Flat 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.

Experimental studies aimed at understanding the fatigue process in metals and polymers have usually been performed under uniaxial stress. Only in the last two decades or so has much experimentation been carried out on fatigue crack propagation under biaxial stress. This paper reviews the available published data. Crack propagation behaviour under biaxial stress is dictated by 3 parameters: stress biaxiality itself, which is defined here as the ratio of the in-plane principal stresses, crack angle with respect to the applied principal stress directions and stress intensity factor range. Depending on the first two parameters. cracks may grow in Mode I, Mode 11 or Mixed-Mode. Crack growth data have been presented using these three divisions. Two short sections have been included on initiation and cyclic stress/strain behaviour under biaxial stress to emphasise the fact that crack growth cannot be fully understood without knowing something of them. The accumulated data do not lead to adequate conclusions on either the qualitative or quantitative behaviour of cracks subject to cyclic in-plane biaxial stress. Reasons for the confusion and even contradiction of independent results are put forward and some discussion given to the possible directions of future experimental work.

No abstract

No abstract

No abstract