13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2.1. Preparation of specimen The rocks used in this experiment investigation are two kinds of granite: white linen granite and red linen granite. They have different grain sizes. The grain size of the former is smaller than later. Specimen contours are both 140mm×40mm×24mm (Figure 1). From specimen central section, in the position L=15mm and L=30mm, an edge crack which width is not more than 1mm were cut by diamond wheel blade. Crack length a＝20mm. Figure 1 Specimen diagram and loading mode Figure 2 Uniaxial compression experiment specimen 2.2. The process of experiment For the finite element method (FEM) calculation subsequently in this paper, the elastic modulus of two rocks under different temperature was measured by uniaxal compression experiments. The contour of uniaxal compression specimen and test situation is shown in Figure 2 and Figure 3. The elastic modulus E measured under different temperature are listed in Table 1. Due to the difficulty of test technique，the Poisson's ratio of the two rocks under different temperatures were not measured except under ambient temperature. And then, about the variation law of Poisson’s ratio in different temperature was not mentioned in published documents. So in this paper Poisson’s ratio are assumed that it has no change when temperature changes; and it is measured under ambient temperature that: for white linen graniteμ= 0.26 and for red linen graniteμ= 0.3. The loading way of abnormal three point bending test is shown in Figure 1. The experimental situation is shown in Figure 4. For the two kinds of granite, under different temperature and different crack position L, the critical fracture loads F measured by experiments are listed in Table 2. Table 1 ：Elastic modulus E of two kinds of granite under different temperatures Elastic modulus E/GPa Type of specimen -500C -250C Room temperature 800C 1600C 2400C White linen granite 18.8685 17.643 15.3455 17.1 18.3985 17.087 Red linen granite 17.033 15.992 17.713 17.56 17.9665 19.196 Whether in high temperature test or in low temperature test, before a test, the specimen must be placed in the oven in which temperature has arrived demand level half an hour in order to get a well-distributed temperature within specimen. In the experimental process, the loading way of test machine was controlled by displacement. Loading rate is 0.015mm/min. In experiment it can be observed that the crack tip point at the bottom of the specimen starts fracture, it leads the specimen failure. The fracture section of specimen is not a plane, and presents a three-dimensional
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