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

Dynamic weight functions are discussed, for arbitrary time-dependent l oading of a plane semi-infinite crack extending at constant speed in a n infinite isotropic elastic body. Then, the weight function appropria te to the case of general normal (or Mode I) loading is constructed ex plicitly, employing Fourier transforms to develop and solve a Wiener-H opf problem. Transforms are inverted by a variant of Cagniard's techni que. The weight function is then employed to develop a relationship, i n the framework of first-order perturbation theory, between the Mode I stress intensity factor and a small but otherwise arbitrary time-vary ing deviation from straightness of the edge of the crack.