1. F. F. Lange, Phil. Mag. 22 (1970) 983.
2. A. G. Evans, ibid. 26 (1972) 1327.
3. D. J. Green and P. J. Nicholson, ?Fracture Mechanics of Ceramics?, Vol. 4, edited by R. C. Bradt, D. P. H. Hasselman and F. F. Lange (Plenum Press, New York, London, 1978) p. 945.
4. J. S. Nadeau and R. C. Bennett, ibid., p. 961.
5. J. C. Swearengen, E. K. Beauchamp and R. J. Eagen, ibid., p. 973.