The Robustness of a Simple Expression for Quantifying Fracture Initiation at a Blunt Flaw

Linear elastic fracture mechanics of cracks is well established, and is based on the stress field near a crack tip being described by the stress intensity factor, with crack extension occurring when the stress intensity factor is equal to a critical value, which is referred to as the fracture toughness of the material. This methodology has been applied to a wide range of materials and structures, with the fracture toughness being related to the micro-mechanistic fracture processes, often via the cohesive-process zone representation of these fracture processes. The author is involved in a wide-ranging research programme whose objective is to extend the fracture mechanics methodology to blunt flaws, so as to take credit for the blunt flaw geometry, the strategy being to parallel, as far as possible, the methods that have been developed for cracks. Earlier work has shown that an appropriate characterizing parameter, analogous to the stress intensity factor for a crack, is the elastic peak flaw tip stress, with fracture initiating when the peak stress attains a critical value, which is related to the flaw geometry, in particular the flaw root radius, and material parameters. A simple expression has been derived for the critical peak stress and, in this paper, we provide support for its robustness.