Defect Detection via Instrumented Impact in Thick-Sectioned Laminate Composites

The application of impact-based nondestructive inspection to thick-sectioned laminate composite parts, although widely reported, is still hampered by a number of challenges. In this article, microphone-recorded impact response variations are associated with delaminations within a variety of test specimens, building in complexity from metal to composite simulant and finally toward the application of the method to hard armor protective inserts. Defective and defect-free states are verified a priori by both operator quality inspections and X-ray computed tomography. Potential delamination-discriminating metrics are determined by signal processing of vibroacoustic data. Prior reported “tap test” metrics that focus on impact force-time histories are shown to be insufficient for thick-sections laminates. The empirical results reported herein, additionally supported by simulations, suggest that large defects may be detectible via a frequency content analysis. Method limitations, potential confounds, and the extension to the case of smaller defects is discussed.