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| EXPERIMENTAL INVESTIGATION ON DYNAMIC FRACTURE OF SOME METAMORPHIC ROCK USING REFLECTED CAUSTICS |
| YANG Liyun，YANG Renshu，ZHAO Xuenan，CHEN Jun，FANG Shizheng |
| (School of Mechanics and Civil Engineering，China University of Mining and Technology，Beijing，Beijing 100083，China) |
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Abstract With a reflected caustics experiment，the dynamic fracture induced by impact loading of some specimens was studied. These specimens processed by mirror transplantation，were made of natural metamorphic rock including white marble，slate and griotte，and rock-like materials including man-made rock and harden cement paste. The results show that the caustics spot of rock-like specimens were recorded at the crack tip，wherever natural rock specimens were not. Then another test to these specimens，which were not processed by mirror transplantation，was carried out with a high-speed photography directly. It is shown that there is a“white banded crack”arising at the surface of natural metamorphic rock specimen，which is different from the rock-like specimen. By contrasting the crack initiation time and propagation velocity between the caustics and high-speed photography test，it is concluded that the micro-crack development and propagation of the natural metamorphic rock specimen processed by mirror transplantation could not be recorded by the reflected caustics，and the transplanted mirror conceals the phenomenon of micro-crack development and propagation，which means that the caustics study on natural metamorphic rock is very difficult.
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2015, Vol. 34 
