FRACTURE-MECHANICS OF BLUNT CRACKS IN A DUCTILE STEEL

The propagation of blunt notches in stainless steel has been studied e xperimentally and analysed using generalized fracture mechanics (GFM), which takes account of inelastic and non-linear deformation. Accordin g to this theory, the critical apparent energy release rate, which is equivalent to J(c), is given by J(c) = k1 (epsilon0) cW0c for an edge crack of length c in a thin sheet (plane stress), where k1 (epsilon0) is a dimensionless function of strain, epsilon0, and W0c is the input energy density remote from the crack at the time of crack propagation. The validity of this equation was demonstrated for blunt cracks and t he function k1 (epsilon0) evaluated. The value of J(c) was measured fo r blunt cracks of different lengths and tip diameters, and also for di fferent crack extensions. J(c) was found to be independent of crack le ngth for the smallest tip radius, but became systematically length-dep endent as the radius increased. However, the dependence of J(c) on cra ck length, tip radius and crack extension can be expressed by a single empirical function, as is suggested by GFM. The propagation of cracks from blunt notches in ductile materials can, therefore, be handled by fracture mechanics methods.