A ductile damage model corresponding to the dissipation of ductility of metal

Abstract

Although some damage models have been proposed for many years, the initiation of ductile macrocracks of metal under complicated stress states can not be appropriately predicted; the reason for this condition is that deformation in fact dissipating ductility of metal is not taken as the starting point of these damage theories. In the present paper, the fundamental principles of irreversible thermodynamics with internal variable are used to establish a ductile damage model, which accounts for the dissipation of ductility of metal due to deformation as the internal damage variable. Moreover, the empirical formula proposed earlier is used to determine the unknown function in the model. Furthermore, the damage evolution of normalized steel 20 in the upsetting process, a complicated deformation process, is studied as an application of this novel ductile damage model. The onset of macrocrack initiation and the evolution of macrocrack are predicted by the model, which agree with those of the experimental observation and therefore indicate that the new ductile damage model reveals the damage evolution in complicated stress states properly.