6. Evaluating Path of Stress Triaxiality to Fracture of Thin Steel Sheet Using Stereovision

A stereovision technique based on digital image correlation is applied to the evaluation of the stress triaxiality and fracture strain of thin steel sheet. A tensile testing specimen with notches made of high strength steel sheet is loaded and the surface displacements are measured from both sides of the specimen surface using two stereovision systems. Not only the in-plane strains but the through-thickness strains are evaluated from the measurement results of the displacements on the both surfaces of the specimen. The variation of the stress triaxiality at an evaluation point is evaluated from the measured strains. The fracture strain is also evaluated from the strain measurement results. Experimental results show that the stress triaxiality and the fracture strain of thin steel sheet can be evaluated by the surface strain measurement. The results can be utilized for simulating deformation and predicting fracture of a component made of thin steel sheet.