| Summary: | 碩士 === 中華大學 === 機械與航太工程研究所 === 87 === The stereo vision is applied to obtain the three-dimensional deformation fields near the crack tip of fracture specimens subjected to combined mode I and II loadings. The fracture specimens used in the experiment are the compact tension shear (CTS) specimens, which were pre cracked in fatigue to obtain the a/b ratio of 0.5. A special loading device was used so that the mixed or pure mode loading can be carried out in the experiment.
In each mixity ratio ( KⅠ/KⅡ), the PMMA CTS specimen was loaded at several loadings until the onset of the crack initiation. The stereo vision system was used to measure the full three-dimensional deformation fields around the crack tip region of the CTS specimen. The crack tip parameters, such as stress intensity factors, KⅠand KⅡ,J integral and crack equivalent angle, were studied.
The strain field near the crack tip of the CTS specimen was obtained by smoothing the measured in-plane displacement field. Using the evaluated strain field and the stress field obtained by Williams, the stress intensity factors KⅠand KⅡwere calculated through the least-squares method by including the higher order terms in the Williams's solution. Results indicate that the equivalent crack angle evaluated by KⅠ/KⅡ is in good agreement with the loading angle when 3 to 5 terms in the Williams's solution are used.
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