Fracture of WC-Co alloys: an example of spatially constrained crack tip opening displacement

This paper attempts, both experimentally and theoretically, to account quantitatively for the propagation of cracks in WC-Co alloys. Evidence is presented which shows that cracks propagate through the ductile Co phase. It is further shown that the square of the quasi static stress intensity factor (KIC) of a slowly propagating crack is linearly related to the Co mean free path. On the assumption that crack tip plasticity cannot extend beyond a single interlayer of Co it is found that the yield stress must be close to twice the theoretical shear stress of Co. Thus, for a particulate composition which consists of grains sufficiently resistant to cleavage and plastic yield, and is bonded by a matrix which is ductile and not susceptible to cleavage, KIC can be calculated. It therefore appears possible, for the first time, to predict accurately from first principles, the fracture toughness of a real elastic-plastic body.