1. W. Spitzig, ASTM STP 453 (1969) 90.
2. R. Bates and W. Clark, ibid 192?214.
3. A. Brother, M. Hill, M. Parker, W. Spitzig, W. Wiebe and E. Wolff, ASTM STP 493 (1971) 3?19.
4. D. Broeck,Engineering Fracture Mechanics 6 (1974) 173?181.
5. D. Harris and D. Elloit, inMechanics and Physics of Fracture (1975) paper 12.