Nonlocal damage modelling for finite element simulations of ductile steel sheets under multiaxial loading

AbstractThe finite element simulation of forming processes or vehicle crash scenarios involves multiaxial loading conditions in general. Thereby, damage and failure in ductile steel sheets is triggered by void growth under hydrostatic tensile loading or by void elongation within a narrow band under shear dominated loading. These different damage mechanisms are considered by a stress state dependent continuum damage model. The damage initiation and failure are represented by a critical and a failure strain. Both are HOSFORD‐COULOMB type functions of the stress triaxiality and the LODE parameter and, thus, incorporate the stress state dependence of the damage mechanisms. Due to the pathological mesh sensitivity for continuum damage models, an enhancement towards nonlocal damage evolution is carried out. Thereby, two options are investigated and compared: the integral nonlocal formulation and the gradient enhanced approach. Finally, the proposed nonlocal ductile damage model is verified for a wide range of stress states by test data of various tensile and shear specimens.