Localization of Impact Damage in Thin-Walled Composite Structure Using Variance-Based Continuous Wavelet Transform

This work is focused on damage localization in thin-walled two-dimensional composite structures. A two-stage low-velocity impact damage with severities of 5 and 9 J is applied to CFRP plate in different positions and a dynamic vibration test is conducted in order to extract the resonance frequencies and corresponding deflection shapes of the structure before and after each stage of damage. Deflection shapes serve as an input for spatial continuous wavelet transform in two dimensions to calculate the damage index and standardize it for every wavelet function. Overall, 16 wavelet functions are used with scale parameters ranging from 1 till 16. The nontrivial problem of scale selection is avoided by computing the variance of normalized scalogram (VNS) over all the scales of consideration for every wavelet. Cross-correlation of VNS values between all the wavelets is performed to reveal the wavelet pairs of similar performance. These wavelet pairs are selected to compute the average VNS (AVNS). Later, a universal threshold is applied to filter the peaks of AVNS to yield the location of damage for each case of severity. Results suggest that a damage can be localized without the consideration of a specific wavelet and scale parameter.