13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- 3.2. The relation between stress intensity factors of initiation points and temperatures After the stress field calculated within the specimens by the finite element method, the three formulas following can be directly applied to calculate the stress intensity factors of the crack tip[10-11]： 0 lim 2 x r K rπ σ Ι → = (2) 0 lim 2 xz r K rπ τ ΙΙ → = (3) 0 lim 2 xy r K rπ τ ΙΙΙ → = (4) r is the short distance from stress point to the crack tip Put r values and stress values of every point on crack extension cord into the formulas, and drew a straight line of KI、KII、KIII v.s. r, through the straight line, the real values of KI、KII、KIII can be got at the point r = 0[10-11]. In abnormal three point bending experiments (Figure 4), the crack fracture just initiated from the tension point which was on the crack tip point located on the bottom of specimen (Figure 4), so the relations between critical stress intensity factors and temperatures are listed in Table 4 and Table 5, and shown in Figure 7 to Figure 10. Table 4 Critical stress intensity factors v.s. temperature (white linen granite) L=30mm L=15mm Temperatures KI/MPam1/2 -KII/MPam1/2 -KIII/MPam1/2 KI/MPam1/2 -KII/MPam1/2 -KIII/MPam1/2 -500C 2.285 0.453 0.248 2.114 0.258 0.148 -250C - - - 2.172 0.265 0.152 Normal temperature 1.772 0.351 0.180 1.794 0.219 0.126 800C 1.721 0.341 0.186 1.682 0.205 0.118 1600C 1.465 0.290 0.159 1.522 0.186 0.107 2400C 1.387 0.275 0.150 1.200 0.147 0.084 Table 5 Critical stress intensity factors v.s. temperature (red linen granite) L=30mm L=15mm Temperatures KI/MPam1/2 -KII/MPam1/2 -KIII/MPam1/2 KI/MPam1/2 -KII/MPam1/2 -KIII/MPam1/2 -500C 2.014 0.399 0.218 2.229 0.272 0.156 -250C 1.626 0.322 0.176 1.734 0.212 0.121 Normal temperature 1.470 0.291 0.159 1.676 0.205 0.117 800C 1.318 0.261 0.143 2.043 0.249 0.143 1600C 0.816 0.162 0.088 1.218 0.149 0.085 2400C 0.794 0.157 0.086 1.083 0.132 0.076
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