The effect of stress biaxiality on fracture initiation at a blunt flaw

From the basis of the cohesive process zone representation of the micro-mechanistic processes that are associated with fracture, the author has, in earlier work, derived a blunt flaw fracture initiation criterion for situations where the process zone size s is small compared with the flaw depth (length) and any other characteristic length, e.g. remaining ligament width, of a configuration, other than the flaw root radius ρ. The criterion gives the critical elastic flaw tip peak stress σpcr in terms of the process zone material parameters and geometrical parameters, and was derived using a two-extremes procedure, whereby the separate and exact solutions for small and large s/ρ values are blended together to give an all-embracing relation that is valid for all s/ρ values. For a wide range of flaw geometry parameters and loading scenarios, it has been demonstrated that σpcr approximately depends on only one geometrical parameter: ρ. In this paper, we show that in the presence of transverse stresses in the direction of the flaw, i.e. with biaxial stress situations, σpcr depends, in a coupled manner, on the flaw shape and the degree of stress biaxiality.