Further investigation of a new continuum damage mechanics criterion for ductile fracture: Experimental verification and applications

The validity and applications of a new continuum damage mechanics (CDM)-based local criterion for ductile fracture proposed by the present author [Engng Fracture Mech. 42, 185-193 (1992)] are further investigated under both proportional and non-proportional loading conditions. A new material parameter denoted W_dc for ductile fracture is emphasized, which has obvious physical meaning and can easily be determined by a macroscopic method. Experimental verification of the stress-state-independence of W_dc is carried out according to a series of new experimental results for more than 20 different materials and/or material states, including carbon and alloyed steels, nodular cast irons and steel welds with various heat treatments, testing temperatures ranging from -140 to 20°C, different tensile speeds and specimen orientations (L and T), etc. The values of W_dc for these materials have been estimated and listed in the paper. It is verified that as a new fracture ductility parameter for engineering materials, W_dc is a material constant independent of stress state and can effectively be employed to evaluate the ductility of various materials and/or material states and to select their heat treatments and welding parameters, respectively. Comparisons of the present criterion with other criteria are presented and some advantages over others are found. The possibility of the CDM criterion as a unified ductile fracture theory for cracked and uncracked solids is also discussed. Particularly, a new mixed mode ductile fracture criterion is proposed, which states that the crack propagates in the direction of the maximum damage integral, denoted Max(W_d), where Max(W_d) reaches its critical value.