| Summary: | 碩士 === 中華大學 === 機械與航太工程研究所 === 95 === Grid method was used to measure the stress intensity factor KI of a mode I fracture specimen. The fracture specimen used in this study was a compact tension (CT) specimen made of 6061-T6 aluminum. A hexagonal grid of dots was pasted along a radial line emerging from the crack tip of the CT specimen. Meanwhile, a set of dot grid was attached to the surface of the specimen at a suitable position. A 2D computer vision was used to acquire the images around the crack tip before and after the deformation of the CT specimen. Then each of the method of single dot and interpolated ellipses was used to measure the magnitude and direction of the in-plane principle strains at the dot centers and interpolating points, respectively. When conducting the fracture experiment, the CT specimen will be subjected to a rigid body motion. While the attached dot grid follows the motion of the deformed specimen, it will not be deformed. Hence the Affine transformation can be used to determine the position and orientation of the deformed specimen relative to the camera so that the effect of the rigid body motion on the strain measurements can be eliminated. Experimental results indicate that when away from the region where the three dimensional effects dominate, the measured strains can be used to accurately determine KI.
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