3D-DIC for non-uniform deformation measurement using affine noncoplanar calibration

Three-dimensional digital image correlation (3D-DIC) has been gradually applied for the deformation measurement of large components. However, this method suffers from full-field matching for uneven deformation during measurement. Conducting targeted analysis and research on 3D-DIC parameters that affect matching accuracy is essential for overcoming this issue. To this end, an optimization strategy for speckle patterns, a noncommon surface calibration method based on affine coordinate correction given the limited calibration accuracy of the existing stereo camera structural parameters, a four-neighborhood full-field matching method based on seed points and the initial value estimation of a second-order shape function, and a second-order shape function initial value estimation method based on reprojection are proposed in this paper. The full-field deformation field is obtained based on the local coordinate system of the surface of the object being measured, and the strain tensor field based on the local coordinate system of the surface of the object being measured is fitted. An equal-strength beam strain measurement experiment is performed to confirm the effectiveness of the 3D-DIC method proposed in this study. The experimental results demonstrate that the proposed method combined with a binocular sensor can achieve a local strain measurement accuracy better than 10με when the off-plane displacement is small.