| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1991: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1990: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
The double-torsion test was carried out to investigate the interaction between stress-induced crack path and mineral grains. Aji granite and Oshima granite were chosen as rock specimen.
First, the double-torsion tests were performed in the way that crack velocities were controlled at range 10^<-7>m/s to 10^<-1>m/s, while the orientation of stress-induced crack was fixed in the direction parallel to the rift plane of Aji granite. After the stressed specimens were dyed, we checked the crack path by thin section analysis using an optical microscope.
The stress-induced crack path was divided into two types, transgranular and intergranular cracks, and each path was subdivided with respect to mineral grains. In spite of the extensive range of crack velocities, the ratios between the transgranular and intergranular crack lengths did not change. The crack paths were all jagged, and often shown detour around the grain boundary when faced with obstacles like hard grains or preexisting cracks. That
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is to say, quartz grain played an important role as such obstacle. Feldspar grain could change the crack path because of its cleavage plane. Biotite grain had serious effect on the path even if its constitution ratio is very small.
Fractal dimensions of the crack paths were calculated by three methods, as indicators of surface roughness. The fractal dimensions were shown in a slight trend with the change of crack velocity. This trend can be explained from the point of limited cracking rate in stress corrosion.
Next, the double-torsion tests were performed under same crack velocity but different orientation, that is, 6 kinds of orientation associated with the three quarry planes. The stress-induced crack paths were observed by the same method as mentioned above. The fractal dimensions were also calculated. Observation by optical microscope indicates that the pre-existing microcracks in quartz play important role in the forming of the stress-induced crack. The slight difference in fractal dimensions associated with the crack path orientation can be explained by the pre-existing cracks oriented preferentially. Less
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