Strain and stress relation until fracture for finite element simulations of a thin circular plate

This paper presents a true strain and stress relation for mild steel that is suitable for the implementation in finite element models. This true strain and stress relation is obtained from a series of tensile experiments with specimens of different length-per-breadth ratios. Unlike the engineering strain and stress relation, the true strain and stress relation is found to be independent of the specimen geometries tested. The use of optical measurements relates the true strain and stress to the finite element length because the strain reference length, being a function of the pixel size, is clearly defined. This true strain and stress relation is used to simulate a plate punching experiment until fracture with the finite element method. The measured element length-dependent failure strain is implemented as a constant strain failure criterion and its applicability is attained through the close triaxiality ranges at failure, both for the tensile and plate simulations.