Evaluating Stress Triaxiality and Fracture Strain of Steel Sheet Using Stereovision

This paper studies a method for evaluating the stress triaxiality and the fracture strains of thin steel plates which are used for an automobile body frame. Three-dimensional displacements and strains on the surface of the thin steel plates are measured using a stereovision. In particular, to measure the through-thickness deformation of the steel plates, the measurements are performed from the both sides of the steel plates. Based on the strain incremental theory, the stress triaxiality is evaluated from the measured strains considering the variation of the thickness of the steel plates. The effectiveness of the proposed procedure is validated by applying it to the evaluation of the stress triaxiality of high strength steel plates. Results show that the stress triaxiality and the fracture strains can be evaluated by the proposed method.