Research On Mechanical Modeling Of Lamb Waves For Structural Health Monitoring Technology

Structural Health Monitoring (SHM) technique based on piezoelectric (PZT) transducer andLamb waves is an active monitoring method, which is widely used for the designing and servicing ofaeronautic and astronautic structures. In this method, PZT transducers can recognize and locatemicro-damages by monitoring the propagation of Lamb waves in the plate structure. However, theresearch and application of Lamb waves are restricted due to their dispersive and multimodal natures.It is worth devoting continuous effort to the investigation towards mechanical characters of Lambwaves propagating. In this dissertation, several known methods were used for the research on PZTtransducers and Lamb waves. Then the analytical model of Lamb waves was established andexperimentally validated. During the process of modeling, the propagating characteristics of Lambwaves were obtained, which can be used for locating sensors, choosing proper monitoring signal,forecasting propagation and wave form of Lamb waves, judging wave modes and estimating damage.The main works and novel researches in this dissertation can be summarized as follows:1. The PZT transducer applied in SHM technique was mechanically and electronically analyzedbased on complex-function method. The mechanical characters of adhesive layer on plate surfacewere also researched. Then the mechanism of both PZT actuator and PZT sensor were established.2. The dispersive characteristics of Lamb waves in both isotropic metal plate and anisotropiccomposties were investigated respectively. The dispersive curves of Lamb waves in both models wereobtained and verified by experiments.3. The excitation of Lamb waves was modeled using PZT actuators and the attenuation of Lambwaves propagating in plates. The displacements and strains of plate structure caused by Lamb waveswere observed. The propagating model of Lamb waves in metal plate was also established based onthe displacements of metal plate structure.4. Following the analysis toward the sensation of Lamb waves by PZT sensors, the amplitudeand phase change of sensor signal were obtained, and then the analytical modeling of Lamb waves inplate structure was achieved. Finally, the results of the analytical modeling of Lamb waves werevalidated by experimentation.