Nature 199, 1282 (28 September 1963); doi:10.1038/1991282a0

Reversed Plastic Flow during the Unloading of a Spherical Indenter

K. L. JOHNSON

Engineering Department, University of Cambridge.

THE process of indentation of a metal surface by a hard spherical indenter has been examined in considerable detail by Tabor¹ and others. If the indenter makes contact with the surface over a circular area of radius a under the action of a load W, the mean contact pressure p _m=W/a ². Tabor showed that plastic yielding begins beneath the surface of the metal when p _m reaches the value 1.1 Y (where Y=yield stress of the metal in simple tension). As the load is increased and a marked plastic indentation develops, the mean pressure approaches a value which is independent of the load given by: where c has a value of approximately 3. This is the state of affairs in a Brinell hardness test.

1. Tabor, D. , Hardness of Metals (Oxford Univ. Press, 1951); Proc. Roy. Soc., A, 192, 247 (1948). | ISI |
2. Tyler, J. C. , Burton, R. A. , and Ku, P. M. , paper presented at the A.S.L.E. Annual Meeting, New York, April 1963.