Composite Structural Health Monitoring Based On Pre-Stack Reverse-Time Migration Method Of Lamb Wave

In this thesis a pre-stack reverse-time migration concept of transient waves signal processing techniques is developed and adapted to guided-wave propagation in composite structure for multi-damage detection by numerical and experimental studies. A composite laminate with a surface-mounted linear piezoelectric ceramic (PZT) disk array is studied as an example. Two types of damages, a straight crack and two circle-shaped inhomogeneities, have been studied. At first, Mindlin Plate Theory is used to model Lamb waves propagating in laminates. The phase and group velocities of flexural waves are also derived from dispersion relations. Then the fundamental narrowband ultrasonic Lamb wave fields in the plate are alternately actuated and received using the linear array distributed piezoelectric transducers before and after damages occurred. Thus the wave fields solely reflected from the damages could be obtained by interpolation. Migration technique is then performed to back-propagate the reflected energy to the damages using a two-dimensional explicit finite difference algorithm and damages are imaged. Stacking these images together yields the final image of multiple damages. According to results, the migration technique provides a promising scheme for in-service monitoring of plate-like composite structures.This research is supported by the National Natural Science Foundation of China under Grant No.50478037 and No.10572058, and by the Science Foundation of Aeronautics of China under Grant No.04I52063.