Experimental and numerical study of delamination detection in a WGF/epoxy composite plate using ultrasonic guided waves and signal processing tools

Reliable damage detection is one of the most critical tasks in composite plate structures. Ultrasonic guided waves are acknowledged as an effective way of structural health monitoring (SHM). In this research, ABAQUS FE package is employed in order to develop a 3D finite element (FE) model to investigate the wave propagating features in a four-layer Woven Glass fiber (WGF) /epoxy composite plate. Dispersion curves have been extracted using semi-analytical finite element (SAFEM) in MATLAB. An experimental study has been done to obtain the sensitivity of the excitation frequency on the delamination detection problem. The Fast Fourier Transform (FFT), Butterworth filtering and the Continuous Wavelet Transform (CWT) signal processing methods have been utilized to extract a more accurate damage sensitive feature from experimental signals.Calculations of amplitude reduction ratio (ARR) for both raw and filtered signals shows that increasing the excitation frequency, which means decreasing the wavelength, leads to increase in the ARR in an approximately linear manner for raw signals, while using the filtered signals for ARR extraction yields higher ARR, peaked at the tuned Lamb mode, which is F=330 kHz in the study. The Butterworth filtering provides larger damage sensitive feature compared to CWT method. Consequently, the ARR is a reliable and enough sensitive feature for delamination detection in composite plates, especially when extracted from filtered signals