1. W.Elber, Engineering Fracture Mechanics 2 (1970) 37?45.
2. T. C. Lindley and C. E. Richards, Proceedings of Mechanics and Mechanisms of Crack Growth, Cambridge (1973) 184?200.
3. M. Kikukawa, M. Jono, and K. Tanaka, Proceedings of the Second International Conference on Mechanical Behavior of Materials, Boston (1976) 716?720.