A novel mirror-assisted multi-view digital image correlation for dual-surface shape and deformation measurements of sheet samples

We propose a novel mirror-assisted multi-view digital image correlation (DIC) method for dual-surface 3D shape and deformation measurements using only a binocular stereo-DIC system and two orthogonal planar mirrors. Through the reflection of the mirrors, virtual surfaces of front and rear surfaces of sheet specimens formed behind the mirrors are simultaneously captured and reconstructed by regular two-camera stereo-DIC. By taking advantage of the speckle patterns premade on the mirrors, reflection transformations of both mirrors are retrieved and used to transform the reconstructed virtual surfaces to their real positions in front of the mirrors. The 3D shapes of both surfaces at each state enable the measurements of full-field 3D deformation on both surfaces and at the third direction (i.e., through-thickness direction). Compared with existing multi-camera DIC methods, the proposed method offers several distinct advantages, such as simple setup, low cost and easy implementation. Real experiments, including dual-surface reconstruction of a coin, in-plane and out-of-plane translation of a plate specimen and full-field deformation measurement of a planar aluminum specimen subjected to uniaxial tensile loading, validated the effectiveness and accuracy of the proposed method. The proposed method opens a new low-cost and convenient avenue for strain measurement in thickness direction, demonstrating great potential in material testing of anisotropic and/or ductile materials.