Wavelet Analysis of Ultrasound for the Detection of Impact Damages in Composite Laminate Structures

Low velocity impact damages (LVIDs) on composite structures can cause critical failure modes like matrix cracking, delamination and fibre breakage. These damages can be difficult to detect if there are no visible surface damage from the impact. Guided wave ultrasonics through active structural health monitoring can sensitively track variations in material stiffness even from low energy transfers due to low velocity impacts. However, the guided wave response may not be clearly interpreted as a significant stiffness change in either the time domain or the frequency space due to dispersion and mode conversion. A wavelet analysis scheme is proposed where the guided waves time signal is decomposed into constituent pseudo frequency scale components to evaluate the zeroth-order moment (ZOM). This is shown to be a promising approach to increase the probability of detection (PoD) of LVIDs located on carbon-fibre reinforced laminate bars interrogated with flexural waves.