A Successive Wavenumber Filtering Approach for Defect Detection in CFRP using Wavefield Scanning

Owing to the high sensitivity of carbon fiber reinforced polymer (CFRP) to internal damages, defect detection through Non-destructive testing (NDT) is deemed an essential task. One of the common methods in NDT to achieve this aim is measuring and analyzing the full-field guided waves propagation in CFRP plates. Scattered waves corresponding to deep defects are usually obscured by other waves due to their weak amplitude. A successful method to highlight these waves is to use wavenumber filtering (WF). However, WF suffers from the assumption that the optimal frequency range of excitation signal is known beforehand, which is not always available. Another drawback is that when more than one type of guided waves mode exist, this method is not capable of highlighting desirable waves or vibrations sufficiently. In this paper, full wavefield images are first constituted by exciting the guided waves via broadband chirp signal and registering them with scanning laser Doppler vibrometery (SLDV). Then, a successive wavenumber filtering (SWF) approach is introduced, which efficiently removes undesirable higher order guided wave modes, and removes the need to know a priori the optimal excitation frequency. Moreover, it is quantitatively and qualitatively shown that the proposed approach could lead to better discrimination between damaged and healthy area than conventional WF.