Deformation measurement across crack using two-step extended digital image correlation method

Abstract In this paper, two-step extended digital image correlation (X-DIC) is proposed to directly measure full-field displacement with discontinuities by using the partition of unity method as the extended finite element method (X-FEM). The displacement variable in the correlation factor of the digital image correlation (DIC) method was expressed by the extended finite element displacement mode; in this way, the two-step X-DIC method combined the basic principle of X-FEM with the DIC method. The approximate displacement of the target area was measured in the first step, and the Newton–Raphson method was used to perform an iterative process to approach the specific displacement values of all the points in the target area in the second step. The reliability of the two-step X-DIC method was verified by the rigid body translation test and the uniaxial tensile test. The results show that this method has better accuracy. This method was also applied to measure the cross-crack displacement field in the uniaxial tensile test and the three-point bending test, and the experimental results indicate that this method has potential as a tool to measure and analyze the deformation field in some discontinuous regions.