Study on Fracture Prediction for Advanced High Strength Steels

-Proposal for Determination of Stress Triaxiality Criterion by Using Simple Tensile Tests and FEM Method-

Abstract

An experimental method and specimens were proposed in order to determine a triaxiality-dependent fracture criterion of advanced high strength steels in the crash simulation of automotive bodies. Some crash tests and simulation results indicated the fracture occurred near the edge or ridge area of the body parts where the stress states are between uni-axial and plane strain conditions. In order to evaluate the fractures and their producing strain states, several types of simple tensile specimens were designed and the local strains during tensile test were measured with a digital image grid method (DIGM). To compute the stress triaxiality and fracture strain, FEM simulation models for several types of tensile specimen with three classes of advanced high strength steels were developed. The relation between fracture strain and stress triaxiality was obtained. The effects of material strength, element types and mesh size on both the stress triaxiality and fracture strain were investigated.