1. N. Claussen, in ?Advances in Ceramics?, Vol. 12, edited by N. Claussen, M. Ruble and A. H. Heuer (American Ceramic Society, 1984) p. 325.
2. R. C. Garvie,ibid. p. 465.
3. P. F. Becher, M. V. Swain andM. Ferber,J. Mater. Sci. 22 (1987) 63.
4. D. B. Marshall,J. Amer. Ceram. Soc. 69 (1986) 173.
5. R. W. Hertzberg, ?Deformation and Fracture Mechanics of Engineering Materials?, 2nd Edn (Wiley, 1983).