Full-field out-of-plane vibration displacement acquisition based on speckle-projection digital image correlation and its application in damage localization

Stereo-digital image correlation (Stereo-DIC) has been widely explored for modal analysis in plate-type structures due to its noncontact and full-field advantages. However, when the traditional stereo-DIC is adopted to capture the out-of-plane displacements, several challenging issues exist such as the development of surface speckles, asynchronous camera recording, and efficiency and accuracy degradation due to high computation costs. Moreover, with the captured out-of-plane displacements, effective and efficient evaluation of the high spatial resolution mode shapes and their application to damage localization are also critical problems. To tackle these issues, a speckle-projection DIC technique using a single high-speed camera is proposed to obtain the out-of-plane vibration displacements. Moreover, an enhanced peak-picking modal analysis method is adopted to enhance the estimation accuracy and efficiency of mode shapes. In addition, the low-rank property of mode shapes in an intact state and the spatial sparse property of damage locations are harnessed for the detection of damage positions without requiring reference data on the healthy state. Finally, the modal analysis and damage localization results based on the proposed speckle-projection DIC are compared with those of the traditional two-camera stereo-DIC technique to verify its feasibility and effectiveness. It is found that the differences in the identified resonant frequencies between these two methods are smaller than 1% for higher modes. Moreover, the proposed speckle-projection DIC has the same accuracy as the traditional two-camera stereo-DIC in terms of measurement accuracy, mode shape estimation, and damage localization.