Damage Visualization of Scattered Ultrasonic Wavefield via Integrated Highspeed Camera System

Abstract

In this study, a damage was successfully visualized through scattered guided acoustic wavefield reconstructed via an integrated high-speed camera scanning system. By employing a sample interleaving and an image stitching technique, the data requisition rate for the high-speed camera was enhanced nearly 250 times in order to overcome the current limited performance due to inadequate on both spatial resolution and temporal resolution, i.e., sampling frequency, for guided wavefield measurement. Further, many experimental parameters, e.g., specimen design, field of view, speckle size and signal frequency, as well as the camera system were carefully designed, integrated and optimized to enable capture of propagating guided waves excited by a piezo actuator on a surface of the structure. As such the in-plane wave displacements could be maximized and extracted using digital image correlation (DIC). A very compliant HDPE plate with an added mass for mimicking damage was chosen for the proof of concept. The first fundamental SH and S0 guided wave modes under continuous wave excitation frequency of 14 kHz were successfully detected by the camera and extracted by DIC, and the disturbance at the damage region was clearly observed in the reconstructed scattered wavefield. A damage imaging condition named wavenumber index (WI) that was previously developed and applied to visualizing the hidden delamination in composites was further adapted and improved for the wavefield reconstructed via high-speed DIC.