On Stress Concentration Factor and Definitions of a Crack and Stress Intensity Factor.

The common assumption that the stress is infinite at the tip of an in-plane crack is inconsistent with the basic historical solutions for stress for cases from which crack formulae have been evolved. The latter formulae do not satisfy boundary conditions. An appropriate definition of a crack, as does one presented here, should make it obvious that such conditions are to be fulfilled and when they are, the meaning of stress intensity factor as the coefficient of a 1square root of r singularity is altered. It no longer represents an infinity of stress and its connection with actual failure stress through a stress concentration factor leads to a fixed, rather than experimental, connection between MOdes I and II stress intensity factors. Furthur discussion of appropriate representations of cracks for shear and normal stress loading is warranted, as well as of toughness definition consistent with failure mechanisms and with elastic-plastic solutions for stress. Author