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3. 3) N. E. Dowling: Cracks and Fracture, ASTM STP601, (1976), p. 19.
4. 4) D. F. Mowbray: Cracks and Fracture, ASTM STP601, (1976), p. 33.
5. 5) C. M. Branco, J. C. Radon and L. E. Culver: Proc. 2nd Int. Conf. Mechanical Behavior of Materials, (1976), p. 632.