A New Digital Image Correlation Method for Measuring Wide Strain Range True Stress–Strain Curve of Clad Materials

Accurate evaluation of the nonlinear hardening behavior (i.e., wide strain range true stress–strain curve) of developed materials as structural materials is essential because it is directly related to user safety and is input data of simulation for plasticity, structural analysis, and sheet forming. However, the conventional methods to measure intrinsic mechanical properties can only characterize homogeneous materials, and the technique to evaluate heterostructured materials such as clad materials is lacking so far. In this study, the nonlinear hardening behavior of the clad material was evaluated using the tensile test and digital image correlation (DIC) to introduce the clad materials into the practical industry. The new method considers the mechanical properties of all layers constituting the clad material by observing the side surface of the specimen, unlike the conventional DIC methods of obtaining the true stress–strain curves from the images of the front surface of the specimen. The reliability of the obtained wide strain range true stress–strain curve calculated using the proposed method was validated using the finite element method simulation. The proposed method can provide trustworthy intrinsic mechanical properties of newly developed clad materials, which are promising next-generation materials.