EFFECT OF T-STRESSES ON THE PATH OF A 3-DIMENSIONAL CRACK PROPAGATINGQUASI-STATICALLY UNDER TYPE-I LOADING

We consider a three-dimensional semi-infinite almost planar crack, pro pagating quasistatically under type I singular loading. Treating the d istortion from planar geometry as a perturbation we evaluate the type II stress intensity factor arising from this distortion including the effect of non-singular T-stresses. Using these results we perform a li near stability analysis by assuming that the crack propagates locally in the direction of pure type I. We obtain a stability diagram as func tion of T-x and T-z reflecting the interaction between the effects due to the T-stresses and the stabilizing effect which arises from the pe rturbed geometry of the crack. From this we infer four types of stabil ity of the crack: monotonous stability, oscillatory stability, monoton ous instability and oscillatory instability. Additionally we find that for certain values of the ratio T-z/T-x a small interval of wavelengt hs of the perturbation will be selected as the crack propagates, so th at the components corresponding to these wave lengths will grow expont ially while all other components are suppressed. Copyright (C) 1996 El sevier Science Ltd.