1. American Society for Testing and Materials, ASTM STP 410, (1967).
2. American Society for Testing and Materials. ASTM Spec E399-72.
3. Heyer, R. H. American Society for Testing and Materials, ASTM STP 527,pp. 1-16.
4. Rice, J. R. Journal of Applied Mechanics, 35,(1968), pp. 379-386.