3D-DIC for Large Displacement With Laser-Based Speckle Patterns

To overcome the limitation caused by the production of surface speckles, digital image correlation (DIC) with speckles generated by the light interference of lasers reflected from rough surfaces has been developed by researchers. However, such speckle patterns are highly dependent on the light path that is determined by the locations of the laser, the target surface, and the cameras, which leads to two problems: 1) the speckle distributions of the same subset are different for cameras of different locations, and thus, 3-D measurements based on stereo cameras are unavailable and 2) the speckle distributions are changing when the target is going through large displacements, and thus, measurements of large displacement are not available. In this article, a method to align the laser speckle subsets in the left and right cameras using printed or projected speckles is proposed to solve the first aforementioned problem, and a speckle updating method is proposed to solve the second problem. An experiment is performed to evaluate the feasibility and the accuracy of the proposed methods with standard DIC measurement results as benchmarks. The result suggests that both the methods provide accurate measurement result. The extra error caused by the method proposed for left–right alignment is minor and that by the speckle updating method is much better than the other existing solution.