1. See for example, F. F. Lange, ASTM Publication 72-GT-56, New York (1972).
2. F. F. Lange, J. Amer. Ceram. Soc. to be published.
3. S. M. Wiederhorn, ibid 56 (1973) 227.
4. A. G. Evans, J. Mater. Sci. 7 (1972) 1137.
5. Idem, Int. J. Frac. Mech, to be published.