DYNAMIC WEIGHT-FUNCTIONS FOR A MOVING CRACK .1. MODE-I LOADING

Dynamic weight functions are discussed, for arbitrary time-dependent loading of a plane semi-infinite crack extending at constant speed in an infinite isotropic elastic body. Then, the weight function appropriate to the case of general normal (or Mode I) loading is constructed explicitly, employing Fourier transforms to develop and solve a Wiener-Hopf problem. Transforms are inverted by a variant of Cagniard's technique. The weight function is then employed to develop a relationship, in the framework of first-order perturbation theory, between the Mode I stress intensity factor and a small but otherwise arbitrary time-varying deviation from straightness of the edge of the crack.