Mesh-Based Digital Image Correlation Method Using Non-Uniform Elements for Measuring Displacement Fields with High Gradient

A new mesh-based digital image correlation (mesh-DIC) scheme using non-uniform 8-node quadrilateral (Q8) elements is proposed to process displacement fields with regions of both high and low gradient. The effect of element size on Q8-DIC is extensively analyzed, and the results show that when the shape function of an element matches or over-matches the gradient of the displacement field, a larger element size can achieve better results. Conversely, when the shape function under-matches the gradient of the displacement field, a suitable element size should be chosen. Furthermore, a practical and effective method based on the residual error of the DIC calculation is proposed to automatically refine mesh with non-uniform elements. The effectiveness of this method is verified using simulated speckle images that contain one- and two-dimensional non-uniform displacements. The proposed method is also used to improve the accuracy of two experiments that measure displacement fields with high gradient.