13th International Conference on Fracture June 16–21, 2013, Beijing, China Fig. 6 Variation of mode-I fracture toughness under confining pressure [8] 5.2 Mode II fracture toughness under confining pressure loading For loading angle 0 θ= °, we usually think that materials will produce the pure mode I fracture. Now, this viewpoint may be reasonable only under without or low confining pressure loading conditions, the fracture mode of materials may be pure mode II fracture around 0°loading angle under high confining pressure. On the other hand, according to the literature [2], for 0 θ= °, 0≡ II K , so the failure of the specimen is no longer pure fracture mechanics problem when the confining pressure coefficient 1 t ≥ . In the literature [8], the critical loading angle of the pure mode II crack was calculated by using the five-term approximation formula proposed by Atkinson et al.[1] which ignored the effects of confining pressure. For example, when =0.3 α , they used 29 cθ = ° . However, according to the present paper, the critical loading angle for pure mode II crack decreases with the increasing confining pressure. 6. Conclusion (1) The stress intensity factors are obtained by using the weight function method in fracture mechanics for the cracked Brazilian disk loaded by the confining pressure, and then the explicit expressions of the stress intensity factors are achieved under both the confining pressure and diametrical forces loading condition, which can be used to calculate the stress intensity factors for any relative crack length and any confining pressure. (2) Analyzed results show that confining pressure significantly influences the mode I stress intensity factors for the cracked Brazilian disk. The mode I stress intensity factors decrease with the increasing confining pressure, however, the confining pressure has no effects on the mode II stress intensity factors. (3) Calculation results show that confining pressure significantly influences the loading condition for the pure mode II crack: as the confining pressure increases, the critical loading angle for pure mode II crack decreases gradually to 0 degree. (4) The fracture mode of materials may be pure mode II around 0°loading angle under high confining pressure loading. Acknowledgements This work was supported by the National Natural Science Foundation of China (project no. 11172186) and the Program for Changjiang Scholars and Innovative Research Team (Project No. IRT1027)
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