Calibration of quantitative shearography for use in local stiffness identification

Shearography is an interferometric method that produces full-field displacement gradients of the inspected surface. In high-technology industry it is often used qualitatively to detect material defects, but quantitative applications are still rare. The reasons for that are the complicated calibration procedure as well as the denoising, unwrapping, the local sensitivity vector estimation and the local shearing angle estimation needed to get quantitative gradient-maps. To validate the technique and its calibration results obtained from shearography are compared to results obtained from scanning laser vibrometry. Beams are acoustically excited to vibrate at their first resonant frequency and the mode shape is recorded using both shearography and scanning laser vibrometry. Outputs are compared and their properties discussed. Separate inverse method algorithms are developed to process the data for each method. They use the recorded mode shape information to identify the beam's local stiffness distribution. The beam's stiffness is also estimated analytically from the local geometry. The local stiffness distributions computed using these methods are compared and the results discussed.