Detection of internal delamination in multi-layer composites using wavelet packets combined with modal parameter analysis

This paper presents a study on active detection of delamination for multi-layer composites using a combination of modal analysis and wavelet transform. The analysis of modal parameters for multi-layer composites with internal delamination is carried out, and energy spectrum of wavelet packet decomposition of structural dynamic response is investigated. For several samples with different delamination dimensions and support conditions, the finite element method is used to study the relationship between delamination dimension and damage-induced change of structural physical property. Results show that delamination leads to a variation of energy dissipation in plate vibration, and it is mode-dependent. For relatively small delamination, the damage-induced changes of natural frequencies and mode shapes are too slight to be detected practically. However, by means of analysis on energy spectrum of wavelet packet decomposition even smaller delamination can be detected using the measured dynamic response signals.