Effects of dynamic loads on internal microstructure of coal by nuclear magnetic resonance(NMR)
ZHAO Hongbao1,2,WANG Zhongwei1,HU Guilin1
(1. School of Resources and Safety Engineering,China University of Mining and Technology,Beijing 100083,China;
2. State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology,Beijing 100083,China)
Abstract:The tests on raw coal and moulded coal specimens under impact loads were performed with the drop hammer impact test device developed in-house. The effects of the number of impact loading,the magnitude of the energy of a single impact,the accumulative effects of impact energy and the energy sequence of impact on the internal micro-structure of coal were studied according to the distribution of T2 spectrum of specimens measured with the nuclear magnetic resonance(NMR) analyzer. The results show that there are some differences between T2 spectrum distributions of raw coal specimen and moulded coal specimen. The quantity and size of internal micro-structure of specimens,especially of raw coal specimens,were increased due to the dynamic loads. The total quantity of internal micro-structure of coal increased nonlinearly with the increase of impact times with a trend of rapid increasing,gentle development and sharp increasing,and increased nonlinearly with the increasing of energy of single impact. Due to the coupling effects of the threshold and absorption rate of impact energy,the accumulative effect of impact loads on internal micro-structure of coal is also nonlinear and has a decreasing trend after the first increase. The accumulative effects of impact loads cannot be simplified as the increasing of the impact energy. The total quantity of internal micro-structure of coal is more sensitive under decreasing cyclic loading than increasing process,so the reservoir can be efficiently stimulated by adjusting the construction sequence in the engineering field.
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