| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 97 === Photoelasticity plays an important role in the stress analysis field. Not only because it is a non-contact whole field optical method, but it provides isoclinic (principal stress direction) as well as isochomatic (principal stress difference) data simultaneously, which are the most important parameters in the fields of stress analysis. But, unfortunately, the coupling between these two parameters induces phase ambiguity problem in the isochromatic data unless the isoclinic data have been correctly procured first. In this work, temporal phase unwrapping is applied to solve the aforementioned problem. Two approaches, loading stepping and different wavelength sourcing, are conducted individually to compare their characteristic differences and limitations. Theoretical and experimental studies show the effectiveness of these two approaches. However, in the load stepping approach the applied loads should be carefully controlled to provide the accurate percentage increment of loading onto the analyzed model and somehow it is more complicate and difficult to control the exactitude of the apparatus for loading than just changing the wavelength of illuminating light source with the other approach. A quarter wave plate error compensation phase stepping skill is employed herein to minimize the chromatic aberration caused by the usage of different wavelengths. In summary, the different wavelength temporal phase unwrapping is easier to be implemented than the load stepping approach in procuring photoelastic stress parameters. The accuracy of results is ensured by a specific phase stepping algorithm, which takes the isochromatic aberration of quarter wave plate into consideration and minimizes it.
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