Nonlinear Ultrasonic Wave Spectroscopy for Detecting Local Defect Resonance Frequency in Delaminated GLARE Plate

Abstract

The structural health monitoring (SHM) technology has received wide acceptance in recent times, where the load-bearing capacity of any structure is a paramount concern. The detection of damage present in the composite structure is quite crucial for better functioning and prolonged service life of a structure. The SHM method based on nonlinear wave spectroscopy (NWS) is a reliable technique for determining the presence of defects in composite structures. The defects in the form of delamination present in composite laminates can be detected by exciting the structure at a critical frequency known as local defect resonance (LDR) frequency of the defect. The excitation of any structure with its LDR frequency leads to an abrupt rise in amplitude of vibration at the defect location and thus leading to high contrast imaging of the defect area. In this paper, a wave propagation study based on explicit dynamic analysis is performed to solve the reverse problem of SHM in thin GLARE plate due to low-velocity impact damages. Moreover, a signal processing technique based on the Fast Fourier Transform (FFT) and bicoherence analysis is implemented for detection of LDR frequency. Two different delamination configurations are considered for single as well as dual excitation cases, in order to prove the efficiency of bicoherence tool in detection of multiple delaminations at different excitations. The LDR frequency obtained from bicoherence analysis is found to be in good agreement with LDR frequencies calculated analytically as well as those obtained from FFT plots. The bicoherence analysis is found to be a reliable and robust tool for detecting LDR frequency and can be used for high contrast defect imaging.