Line-Focused PVDF Transducer and Defocusing Method for Measuring Cylindrically Guided Waves and Acousto-Elastic/Plastic Effects
| Autor: | Chun-ILin, 林峻毅 |
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| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 Lens-less line-focused PVDF transducers and defocusing measurement method are applied to determine the dispersion curves of cylindrically guided waves, including Rayleigh-like cylindrical surface waves propagating along the circumferential direction of solid cylinders and layer-coated cylinders, as well as cylindrical Lamb waves on circular annuli. Conventional V(f,z) waveform processing method has been modified to cope with the non-linear relationship between the phase angle of wave interference and the defocusing distance. A cross correlation method is proposed to accurately extract the cylindrically guided wave velocity from measured data. Experiments have been carried out on: (1) stainless steel and glass cylinders, (2) Ni-coated stainless steel cylinders, and (3) cylindrically curved stainless steel sheets. The experimentally obtained dispersion curves are in very good agreement with their theoretical counterparts. Variation of cylindrically guided wave velocity due to the cylindrical curvature is quantitatively verified using this method. Line-focused PVDF transducers and its V(f,z) defocusing measurement system are also applied to determine the acoustoelastic and acoustoplastic effects of deformed polymethylmeth-acrylate (PMMA) samples, as well as silicon steel samples with permanent deformation. Different levels of strain or permanent deformation are formed in PMMA and silicon steel samples. Large plastic deformation ranging from 5% to 30% is created in the silicon steel samples using uni-axial tensile loading. The velocity changes of surface acoustic waves under different strain or plastic deformation are measured along various directions relative to the loading direction. The acoustoelastic coefficients of PMMA are successfully determined from measurement results. The acoustoplastic effects of PMMA and silicon steel samples are also measured and determined. The investigation on the acoustoelastic and acoustoplastic effects demonstrates an effective way for estimating applied and/or residual stresses in solid materials nondestructively using the line-focused PVDF transducer and its measurement method. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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