Modelling of nonlocal damage and failure in ductile steel sheets under multiaxial loading

Abstract

A continuum damage model is proposed capturing the influence of damage on the stress tensor for ductile steel sheets under multiaxial loading conditions. The model consists of a critical strain, representing damage initiation, as well as a failure strain. Both are Hosford-Coulomb type functions of the triaxiality and the Lode parameter. In order to prevent the pathological mesh-sensitivity for continuum damage models, the approach is extended towards nonlocal damage evolution. Thereby, two different established methods are compared: the integral based nonlocal formulation and the gradient enhanced damage method. A critical assessment of both methodologies is carried out by comparing the simulation results with test data of various tensile, shear and biaxial specimens, made of the microalloyed steel HX340LAD. The outcome demonstrate the superiority of the gradient enhanced approach for industrial applications, since nearly the same prediction accuracy is obtained as with the integral nonlocal approach, but the simulation time is significantly shorter.