Three‐dimensional Displacement and Shape Measurement with a Diffraction‐assisted Grid Method

Abstract

ABSTRACTThe grid method is a full‐field optical technique for computing surface displacements and strains of a material by analyzing the phase of grid lines patterned on the specimen. To date, most experiments using the grid method have measured only two‐dimensional in‐plane deformations. Here, the grid method is extended to three dimensions by using a crossed grid pattern and a diffraction grating which enables acquiring images from multiple viewing angles on a single camera. In‐plane displacements and strains are computed using the conventional grid method, and the corresponding three‐dimensional (3D) displacements—including out‐of‐plane displacements or shapes—are computed by analyzing the images collected at different viewing angles. The technique is demonstrated by measuring 3D rigid body motion, the 3D displacements of a membrane in a pressure‐bulge experiment, and the out‐of‐plane curvature of a cylindrical specimen.