Critical assessment of the application of the J-integral and CTOD concepts to circumferentially cracked copper bars

Abstract

The aim of this work is to explore experimentally the validity of the concepts of J-integral and crack tip opening displacement for characterizing the stress and strain state at the tip of an axisymmetrical crack in a bar undergoing large plastic strain before crack extension. The tests are made on extruded copper round bars presenting a very high ductility. Three different analytical formulations of the J-integral proposed in the literature for circumferentially cracked bars are compared at initiation of cracking. The limit between shallow crack and deep crack geometries is experimentally demonstrated. It is found that, in neither of these geometries, J and δ_CTOD are dominant. However, the ratio J_c/δ_c is constant for deep cracks, which suggests an alternative fracture criterion consisting in postulating the dissipation of an average critical energy per unit volume until crack extension.