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2. Yi Zhijian, Journal of chongqing Jiaotong Institute 10:3 (1991) 37?41, in Chinese.
3. Yi Zhijian, Engineering Fracture Mechanics 42:5 (1992) 833?840.
4. Wang Qizhi, International Journal of Fracture 59:2 (1993) R39-R43.
5. Wang Qizhi, International Journal of Fracture 62:3 (1993) R57-R61.