Shadowed delamination area estimation in ultrasonic C-scans of impacted composites validated by X-ray CT

Although ultrasonic pulse-echo C-scanning is a mature non-destructive evaluation technique for imaging internal damage in composite structures, a major impediment of obtaining a full characterization of the internal damage state is delamination shadowing effects. Specifically, shadowing refers to regions of interest that are behind other delamination planes or discontinuities with respect to the scanning surface. The delamination planes block ultrasonic wave transmission and the regions of interest are thus hidden (i.e. shadowed) from the scan. A methodology has been developed to expand ultrasonic scan data of impacted composites by utilizing damage morphology information that is well established in the composite impact research community, such as matrix cracks bounding delaminations, to estimate shadowed delamination information and matrix cracking. First, impacted flat composite plates were C-scanned by pulse-echo ultrasonic and the results were segmented by depth of damage to establish interface-by-interface delamination information. These delaminations were then fit by bounding lines representing the fiber/matrix crack directions defined by the orientations of plies adjacent to each interface to estimate the shadowed portion of the delamination results. The area inside this boundary was added to the original ultrasonic delamination area to create an estimation of the full delamination state at each shadowed interface. Additionally, because this extension method is based on the interactions between delaminations and matrix cracking, this extension method provides an approximation of the matrix cracking of adjacent plies. Results were compared with X-ray computed tomography scans to assess the effectiveness of the extension method.