Regularized Global Digital Image Correlation Method for Crack Tip Deformation Field Measurement

Crack tip deformation field measurements are crucial for the quantitative study of material fracture characteristics and behavior. Subset-based digital image correlation (DIC) is commonly used for this purpose; however, results obtained across the crack are meaningless and are faced with under-match problems in measuring complex deformation fields around the crack. To solve these problems, we propose the Hermite-element based regularized global DIC (HRGDIC) method for deformation field measurements around the crack. HRGDIC uses the high order Hermite element function to construct each finite element in global DIC, and it establishes an iteration method that simultaneously considers the gray-scale error and the displacement field smoothness. During each iteration, the generalized cross-validation method is used to obtain the optimum regularization parameter. Therefore, the proposed HRGDIC method can not only handle the complex high-gradient deformation around the crack tips but also produce smoothed displacement and strain fields at the end of the iterations. Simulations and experimental results of crack tip deformation images show that compared with the traditional local DIC, the proposed HRGDIC has higher measurement accuracy, and it is an effective method for solving the high-gradient deformation field measurement problems around crack tips. © 2020, Chinese Lasers Press. All right reserved.