1. D. Tabor, “The hardness of metals” (Oxford University Press, London, 1951).
2. X. Cai, Dissertation, Technische-Universität Wien (1988).
3. L. E. Samuels, ASTM STP 889, (1986) p. 5.
4. T. O. Mulhearn,J. Mech. Phys. Solids 7 (1959) 85.
5. X. Cai,J. Mater. Sci. 11 (1992) 1527.