Abstract
This paper describes a method of finite strain measurement and subsequent stress computation of sheet steel specimens undergoing plastic deformation. A notched sheet specimen made of high-strength steel under a tensile load is observed using stereo vision. The displacement is then determined using stereo digital image correlation. A procedure for estimating the finite strain and corresponding stress from the measured in-plane displacement is presented. First, the deformation gradient tensor is determined. The logarithmic strain components are then determined from the right stretch tensor determined from the deformation gradient tensor. Finally, the stresses are evaluated from the strains based on the plasticity theory. The effectiveness of the proposed method is demonstrated by applying it to the evaluation of the stress triaxiality with the progress of the deformation and the identification of material properties after necking using the virtual fields method. Results show that the stresses in the plastically deformed region can be obtained by the proposed method.
