Impact damage detection in woven CFRP laminates based on a local defect resonance technique with laser ultrasonics

Abstract

This paper presents a local defect resonance (LDR)-based approach to detect barely visible impact damages (BVIDs) in woven CFRP laminates using laser-ultrasonic guided waves. In the experiments, broadband guided waves were excited by an Nd:YAG pulsed laser to induce resonant vibrations of BVIDs. The laser was scanned on the designed area of the woven CFRP laminates by using a galvano mirror system. A fixed broadband PZT sensor received the waves propagated from all the laser irradiation points and the datasets of the recorded waveforms were further processed to visualize the wavefield in the scanned area. A robust post-processing method was proposed to extract automatically the LDR frequencies and to obtain the image of the BVID. The feasibility of the proposed method was well validated on a woven CFRP laminate with a single BVID. In order to evaluate the detection performance, we compared our proposed method with other traditional methods, i.e., root mean square (RMS) and weighted RMS. As a result, it was found that our proposed post-processing procedure could visualize the BVID with higher contrast. Furthermore, the detection of multiple BVIDs using the developed method was demonstrated successfully.