Ductile fracture of hydrostatic-stress-insensitive metals using a coupled damage-plasticity model

In this paper, a new coupled damage-plasticity model is proposed to predict plastic response and ductile fracture for two hydrostatic-stress-insensitive metals. A convenient hybrid experiment-simulation approach is designed to calibrate model parameters. Geometry transferability of model parameters is validated to various notched tensile specimens. With the characteristics of the present constitutive model, the critical damage parameter is demonstrated to be an appropriate fracture criterion, where fracture strains of various notched tensile specimens are in good agreement with experimental data. The study also reveals that there exist complementing mechanisms for the stress-triaxiality-dependent damage evolution and strain hardening of effective (undamaged) stress, respectively, that result in the non-uniform distribution of overall (damaged) equivalent stress-strain curves on the minimum cross section of tensile specimens. Then, it is the combined effect of non-uniformly distributed overall equivalent stress-strain curves that results in the phenomenon of hydrostatic-stress insensitivity in metals.