Damage Detection And Identification For Composites Using Stress Waves And Time-frequency Analysis

One of the critical tasks in the research of structural integrity for future's aircraft is to continuously on-line monitor the advanced composite structure in (near) real-time. This study presents a preliminary study on the piezoelectric-based built-in structural health monitoring system which can be integrated seamlessly into the composite structure. A damage detection and identification method using Lamb waves and time-frequency analysis is proposed for continuously monitoring of composites, detecting the damage in near real-time, localizing it accurately, sizing it approximately and visualizing it finally.In this study, Lamb waves propagating in anisotropic laminates are first modeled analytically using higher-order plate theory and the direction-dependent dispersion relations of the waves are established. Finite element analysis is employed to simulate the wave propagation in anisotropic composite structure. Wavelet transform is applied to the wave signals actuated and sensed by piezoelectric transducers in the time-frequency domain to extract the characteristic information such as time arrival to measure the actual wave group velocities propagating in composite laminates and compare them with the results given by plate theory. Combined with the theoretically computed and actually measured wave velocity, a genetic algorithms optimization technique is employed to identify the location and size of the damage. A damage imaging approach is adopted and improved to image the damage. The applicability and effectiveness of the proposed method is demonstrated by experimental studies.This research is supported by the National Natural Science Foundation of China under Grant No.10572058, and by the Science Foundation of Aeronautics of China under Grant No.04I52063.