The Correlation Between Hardness (Mean Contact Pressure by a Spherical Indenter) and Flow Stress

This paper deals with the correlation between hardness (mean contact pressure) P_m by a spherical indenter and flow stress Y under the uniaxial stress field. Firstly, the mean strain of the deformed material around the indentation ε_<ic>, which corresponds to the total strain under the uniaxial stress field, is defined following Tabor's idea. Secondly, hardness/flow stress ratio C is obtained experimentally for C =9.8 P_m/Y, where Y is in MPa, and formulated for two conditions of material (1) elastic-plastic transient process : C=1.1+(2/3) ln(ε_<ic> E_s/Y), (2) ideal-plastic deformation : C=2.9; E_s is the Young's modulus of a material. Finally, by combining these relations, a method of estimating the flow stress-strain characteristic curve by spherical indentation is proposed. In addition, an example of estimation of the flow stress-strain characteristic curve of SUS 304 is shown over a wide range of strain by means of the proposed method