Non-destructive Inspection of Contaminated Epoxy Plates Using Propagating Acoustic Waves

The increased use of composites demands the development of repair processes that can guarantee lasting strength restoration so as to minimize the frequency of expensive downtime. Weak bonds are a concern for ensuring the structural integrity of a repair and although epoxy resins are continuously being developed to have higher strengths than their predecessors, factors such as contamination levels in the repair bond may result in poor adherence and inhibit overall bond strength. This research compares the response of virgin epoxy plates to short duration acoustic excitation with that of epoxy with varied levels of contamination (0.5, 1 and 10%). Acoustic events were simulated at multiple distances from a high-fidelity displacement sensor, using the Hsu-Nielsen technique, and the experimental signals were then assessed in the time–frequency domain, using the wavelet transform. Results were then compared with previous research on unidirectional carbon fiber laminates with a single contaminant in between plies.