A damage evolution model considering void shape effect and new damage level definition

• A novel damage level definition was given considering ellipsoid void evolution. • A new damage model was deduced based on both void volume and shape change. • Damage distributions and evolution significantly change with specimen shapes. • Specimen shape has notable impact on fracture characteristics and void evolution. Metal fracture under different stress states is one of the most concerned problems in engineering field. Damage evolution model is of great value to intensive comprehension on fracture mechanism and its engineering application. In this paper, considering that fracture surfaces are formed by void evolution, a new damage level with clear physical significance was defined as the ratio of the maximum statistical cross-sectional area of voids to the cross-sectional area of the representative elements. Combined with this new damage level, a novel damage evolution model was established based on void nucleation, uniform growth and shape change. Subsequently, two groups of quasi-static tensile tests were conducted. One group was called fitting group and used to fit numerical model parameters. Another one was called analysis group and chosen to investigate fracture and void evolution. DIC analyses and SEM tests were also carried out to analyze the influence of specimen shapes on strain distribution and void evolution. Moreover, the damage evolution model was applied to the numerical simulation to verify its reliability. The numerical results were basically consistent with the experimental results by comparing the force-displacement relationships, fracture strains, void number density distributions and void ellipticity distributions. The effects of specimen shapes on damage and void evolution were specifically investigated by numerical simulation. All results illustrated the proposed model provides a tool for predicting quasi-static ductile fracture under different stress states and has guiding value for engineering design.