Comparison of time dependent fracture in viscoelastic and ductile solids

Effects of two parameters on enhancement of the time-dependent fracture manifested by a slow stable crack propagation that precedes catastrophic failure in ductile materials have been studied. One of these parameters is related to the material ductility (rho) and the other describes the geometry (roughness) of crack surface and is measured by the degree of fractality represented by the fractal exponent alpha, or - equivalently - by the Hausdorff fractal dimension D for a self-similar crack. These studies of early stages of ductile fracture are preceded by a brief summary of modeling the phenomenon of delayed fracture in polymeric materials, sometimes referred to as creep rupture. Despite different physical mechanisms involved in the preliminary stable crack extension and despite different mathematical representations, a remarkable similarity of the end results pertaining to the two phenomena of slow crack growth that occur either in viscoelastic or ductile media has been demonstrated.