Impact damage assessment in composite structures based on multiwavelet analysis of modal shapes

The low-velocity impact damage of composite structures is an important problem in various industrial branches, especially in the aircraft and aerospace industriess. Due to the nature of impact damage initiation and propagation and its poor ability of detection based on surface inspection, the appropriate non-destructive damage assessment methods need to be developed. One of the extensively developed groups of methods is the technique based on modal testing and further processing of modal shapes using wavelet analysis. Since the wavelet analysis is very sensitive to even small abrupt changes in an analyzed signal, this approach is chosen for extraction of diagnostic information. In the following study, the novel approach based on multiwavelet analysis of modal shapes, achieved from measurements using a laser vibrometer, is applied to the composite plates damaged following various scenarios. Based on the comparative study, the Donovan-Geronimo-Hardin-Massopust multiwavelet is selected as the best for evaluation of damage sites. The proposed algorithm makes possible detection and localization of cracks and accompanying delaminations, resulted from the impact loading, with high precision, which is verified by comparison with ultrasonic C-scans of the analyzed plates. The obtained results allow for application of the presented method in the industrial non-destructive testing as well.