Impact damage imaging for composite structures using guided wave techniques with 3D digital image correlation

This paper presents an integrated system capable of damage imaging of barely visible impact damage (BVID) in composite structures. This system applies guided-wave-based structural health monitoring using 3D digital image correlation, or GWSHM-3D DIC to produce a map of subsurface damage using a short video from a stereo pair of synchronized digital cameras. The proposed system overcomes many limitations of previous efforts of GWSHM that used 2D digital image correlation (DIC). First, 3D DIC can capture the higher-amplitude out-of-plane displacements associated with the anti-symmetric wave mode, lowering the spatial resolution requirements of the cameras. Second, a total wave energy (TWE) imaging condition is employed that uses the monogenic signal via a Reisz transform to obtain the local instantaneous amplitude as a contribution to wave energy. This condition can highlight local resonance in the damage region without the need for high frame rates to fully reconstruct the wavefield. With significantly lowered spatial and temporal resolution requirements of the cameras, high-stiffness materials like composites can be inspected or monitored with a larger field-of-view (FOV). Additionally, signal enhancement techniques intended to increase the effective resolution of the camera are no longer necessary, which reduces the data acquisition time from many hours to a few seconds. To demonstrate this integrated dual-camera concept with the TWE imaging condition, the system was used to image damage in a CFRP composite sandwich panel that had been subjected to a low-velocity impact. Initial damage maps produced for a 100-mm x 100-mm FOV using a three-second video pair show precise damage imaging ability that is comparable to benchmark ultrasonic and x-ray scans. This efficient and reliable integrated system demonstrated high potential for in-time damage inspection on composite aircraft and other critical structures.