Evaluation of large plastic deformation for metals by a non-contacting technique using digital image correlation with laser speckles

Abstract

The full-field deformation characterizations of a metal undergoing large plastic strains are difficult to be obtained from the conventional true stress-strain curves. In this study, we proposed using a simple non-contacting technique, digital image correlation (DIC) with laser speckles, to evaluate large plastic deformations of metals, especially for thin metal foils and for the forming at high temperatures. The feasibility and accuracy of this DIC technique were confirmed by conducting uniaxial tensile tests using different materials. As results, the measured strains indicated a good accuracy with an error range of 6% in measuring the large plastic deformation at room temperature and 10% in measuring a large strain up to 0.6 at a high temperature of 400 °C. The strain distribution measured by DIC with laser speckles and with artificial speckles showed good agreement, confirming the feasibility of this DIC technique for measuring large plastic deformations. By using this technique, the evolution of plastic zone was successfully investigated for thin metal sheets with a thickness of 0.5 mm. Furthermore, the strain fields involving localizations of 50 μm thick metal foils forming at room temperature and a large plastic deformation of metal tubes forming at 400 °C were evaluated qualitatively and quantitatively.