In one of the non-destructive testing techniques, Lamb waves, because of its ability to propagate a long distance and being hard to attenuate, can detect a wide range of area. However, due to its multimodal and dispersive characteristics, identifying the signals of defects during the test is often difficult. Time reversal method, a self-focusing technique, can offset the dispersion of Lamb waves and effectively focus on the spatial and temporal domain. This study applies the finite element method to stimulate the propagation of Lamb waves on an aluminum plate, selecting four sets of frequency-thickness products and two excitation types to excite the single-mode or multimode Lamb waves. This study aims to discuss the effects of modal and dispersion on the focus of the time reversal methods. The results show that 2 MHz-mm and in-plane excitation can produce numerous, more dispersive modals with the best focus effect. If we applied the time reversal method to testing the defects of Lamb waves, and the defects are circular and longitudinal notches, then, according to the results, the reflection signal amplitude of the circular defects can be highly increased. According to the test results of small-sized notches, the time reversal method cannot effectively improve the detecting ability of this defect.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0820110-083024 |
| Date | 20 August 2010 |
| Creators | Huang, Yi-chung |
| Contributors | Shao-Yi Hsia, Yi-Cheng Huang, Bor-Tsuen Wang, Shiuh-Kuang Yang, Shyue-Jian Wu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0820110-083024 |
| Rights | not_available, Copyright information available at source archive |
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