13th International Conference on Fracture June 16–21, 2013, Beijing, China For ' =0 II K , '' '' ' II II II II K K K K = + = , which means that confining pressure cσ has no effects on mode II stress intensity factor. Eq. (12) can still be used to calculate mode II stress intensity factors under both confining pressure and diametrical forces loading condition. 3. Effects of confining pressure on stress intensity factors To investigate the effects of the confining pressure on the stress intensity factors, according to Eq. (15), we take t =0.1、0.5、1.0, respectively, and calculate the mode I stress intensity factors IF for different relative crack length αand loading angle θ. The calculated results are shown in Fig.4. 0 20 40 60 80 100 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 FΙ θ(deg) α=0.2 α=0.3 α=0.4 α=0.5 α=0.6 α=0.7 (t=0.1) (a) t=0.1 0 20 40 60 80 100 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 FΙ θ(deg) α=0.2 α=0.3 α=0.4 α=0.5 α=0.6 α=0.7 (t=0.5) (b) t=0.5 0 20 40 60 80 100 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 FΙ θ(deg) α=0.2 α=0.3 α=0.4 α=0.5 α=0.6 α=0.7 (t=1.0) (c) t=1.0 Fig.4 Normalized stress intensity factors ΙF for different confining pressures In addition, in order to further analyze the effects of confining pressure on the stress intensity
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