Shadowed Delamination Area Estimation in UT C-Scans of Impacted Composites Validated by X-Ray CT

摘要

Although ultrasonic C-scanning (UT) is a mature non-destructive evaluationtechnique for imaging internal damage in composite structures, a major impediment ofobtaining a full characterization of the internal damage state is delaminationshadowing effects. Specifically, shadowing refers to regions of interest that are behindother delamination planes or discontinuities with respect to the scanning surface. Thedelamination planes block ultrasonic wave transmission and the regions of interest arethus hidden (i.e., shadowed) from the scan. A methodology has been developed toexpand UT scan data of impacted composites by utilizing damage morphologyinformation that is well established in the composite impact research community, suchas matrix cracks bounding delaminations, to estimate shadowed delaminationinformation and matrix cracking. First, impacted flat composite plates were C-scannedby pulse-echo UT and the results were segmented by depth of damage to establishinterface-by-interface delamination information. These delaminations were then fit bybounding lines representing the fiber/matrix crack directions defined by the plyorientations adjacent to each interface to estimate the shadowed portion of thedelamination results. The area inside this boundary was added to the original UTdelamination area to create an estimation of the full delamination state at eachshadowed interface. Additionally, because this extension method is based on theinteractions between delaminations and matrix cracking, this extension methodprovides an approximation of the matrix cracking of adjacent plies. Results werecompared with X-ray computed tomography scans to assess the effectiveness of theextension method.