| Summary: | 碩士 === 雲林科技大學 === 機械工程系碩士班 === 98 === Digital image correlation (DIC) is a whole-field, non-contact, and non-destructive strain measuring method. This method captures the surface image of a specimen before and after the deformation, and then the strain as well as displacement information of the specimen can be obtained by analyzing the change of the images. In this work, a two-step DIC is presented. In the first step, the coarse-fine iterative technique is used to search the displacement of an interested region of the specimen, and then the strain can be obtained by utilizing the finite element method in the second step. To verify the accuracy of this method, an ideal experiment which prevents the error from the CCD sensor, lighting or other experimental error resource is used. In order to find the characteristic of the speckle pattern on the surface of the specimen that benefits to DIC, some different combinations of random speckle pattern are tested. The affection of image filter (wiener2) to DIC is also discussed, and the result shows that it could improve the image quality to reduce about 30% strain error. In addition to a single point, this method can provide the strain and displacement information for a region near a high strain area, which is around a hole in a uniaxial tensile testing plate. Moreover, this method is used to find the stress intensity factor of a specimen with an edge crack. Finally, this method is used in the uniaxial tensile testing for PDMS specimens without artificial painting on the surface, and the obtained Young''s Modulus is around 1.87~2.77Mpa which is close the results in the literature.
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