Photomechanics evaluation combining fringe projection and digital height correlation

Fringe projection (FP) is one of the most widely used method to precisely measure the 3D geometry of complicated surfaces. However, when the object is in motion, it is difficult to estimate the motion or displacement that happens between the frames. The most commonly used method for estimating the in-plane displacement is Digital Image Correlation (DIC). It has been widely used in the area of experimental mechanics. As the traditional DIC method uses a single camera, it is difficult to recover the 3D shape of the object. In this paper, we propose a novel method called digital height correlation method for measuring surface profile deformation. The height data obtained from FP can be used to estimate the deformation. The proposed method involves measuring the 3D profile of an object, which has rich surface topographic variations using a high-accuracy fringe projection method. Then, the 3D profiles obtained from the before and after displacement state are correlated to extract the displacement map. Specifically, the out-of-plane displacement is extracted by applying the correlation technique to the height map obtained from the 3D profile of the object. The accuracy and efficacy of the digital height correlation method are validated using rigid-body translation tests and tensile tests of a rubber specimen. Experiments conducted will demonstrate the success of the proposed method.