1. A. G. EVANS, ?Fracture Mechanics of Ceramics? Vol. 3, edited by R. C. Bradt, D. P. H. Hasselman and F. F. Lange (Plenum Press, New York, 1978) p. 301.
2. B. R. LAWN and D. B. MARSHALL,ibid p. 205.
3. A. G. EVANS, ASTM STP No. 678 (1980) p. 112.
4. N. MIYATA and H. JINNO,J. Non-Cryst. Solids 38 (1980) 391.
5. F. F. LANGE,J. Mater. Sci. 17 (1982) 240.