13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- From the Figures above，it can be seen that the absolute values of critical stress intensity factors decrease with the temperature increase. It is unconcerned with rock type and crack positions L. The reason is the critical fracture loads decrease with the temperatures increase, so the critical stress intensity factors KI、KII、KIII decrease relevantly. From the Tab. 4 and Tab. 5, it can be seen that the KI (>0) values at the initiation points for L=30mm specimen are generally smaller than the KI (>0) values for L=15mm specimen. And the critical loads of the former are generally bigger than the latter. From this it can be known that, let the L=30mm specimen failure is more difficult than let the L=15mm specimen failure. But the relevant absolute values KII and KIII of former are bigger than latter. It shows that, if KI value who dominates the crack fracture initiation is not big enough, a I-II-III mixed mode rock crack tip can begin to expand, it has to have bigger KII and KIII values. This result reflects a comprehensive effect of mixed mode rock crack fracture sufficiently. 4. Conclusion (1) In the range of -500C to 2400C, with the increase of temperature, the variation of elastic modulus E of two kinds of granite is not obvious; i.e. E values had no obvious differences between ambient temperature and some other temperature levels. (2) For the same kind of rock crack specimen, with the increase of temperature, the critical fracture load is gradually reduced. The deviation rate η decrease gradually from ( 20% to 40% ) under -500C to ( -20% to -40%) under 2400C, i.e. at the lower temperature -500C, the crack initiation load will be higher ( 20% to 40% ) than at ambient temperature; at the higher temperature +2400C, the critical fracture load will be lower ( 20% to 40% ) than at ambient temperature . (3) For the same specimen, the critical stress intensity factor KI, KII, KIII, at the crack fracture point, decrease with the temperature increase. (4) At the same temperature, the longer the distance between crack and center of the specimen, the value of KI (caused by tensile stress) in crack fracture point will be lower; and the critical load will be higher. It reflects the rock crack fracture initiation is mainly caused by tensile stress. If the KI value is smaller, is the higher absolute value of KII, KIII at crack fracture initiation point required. It reflects the comprehensive effects in I-II-III mixed mode rock crack fracture. Acknowledgements This study is financially supported by Natural Science Foundation of China (No: 41072242) and National Basic Research Program under Grant No. 2010CB226802, 2011CB201201. References [1] Xu Xiaoli , Gao Feng , Ji Ming. Damage Mechanical Analysis of Fracture Behavior of Granite Under Temperature[J]. Journal of Wuhan University of Technology, 2010, 32(1):143-147. [2] T Funat su, M Seto, H Shimada, et al. Combined effects of increasing temperature and confining pressure on the fracture toughness of clay bearing rocks[J]. International Journal of Rock Mechanics and Mining Sciences, 2004, 41(6): 927-938. [3] Zuo Jianping, Zhou Hongwei, Liu Yujie. Research on characteristic parameters of sandstone three-point bending failure under different temperatures[J].Chinese Journal of Rock Mechanics
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