A damage model that can be coupled with constitutive behavior prior to necking for SGAFC 780 steel

A coupled phenomenological damage model has been proposed that can be flexibly coupled with constitutive behavior even before necking occurs. This model employs Banerjee’s damage accumulation scheme, the Johnson–Cook fracture strain curve, and the Kachanov–Rabotnov coupling scheme. A modified Voce hardening law was employed to describe the constitutive behavior. Four types of sheet specimens were prepared using SGAFC 780 steel for tensile fracture tests. These specimens include center-holed, round-notched, U-shaped notched, and shear specimens, designed to encompass a wide range of triaxiality levels. The parameters of both the proposed damage model and the constitutive model were inversely identified by tracking the experimentally measured load–displacement curves through repeated FE analyses using an optimization algorithm. The identified parameters demonstrated coupling from the pre-necking stage and accurately replicated the measured load–displacement curves for not only the four types of specimens used to calibrate the models but also for the specimen subjected to the standard tensile test. They also predicted damage contours that reasonably correspond to the moments and locations of cracks observed during the tensile fracture tests. By integrating these findings with the characteristics of the flexible coupling onset point in the stress–strain curve, it is likely that the proposed damage model can effectively characterizes the deformation and fracture behavior of a diverse range of materials.