A universal relationship between indentation hardness and flow stress

A new indentation hardness (H) approach to evaluating the true stress (sigma)-true plastic strain (epsilon) constitutive behavior of materials is described. Extensive elastic-plastic finite element (FE) simulations were carried out to assess the relation between H and sigma(epsilon). The analysis led to derivation of a universal relation between H and sigma(epsilon) given by H approximate to 4.05(134.6 sigma(flow) /E)sigma(flow) where sigma(flow) = sigma(y) + <sigma(sh)>, <sigma(sh)> is the average strain hardening between epsilon = 0 and 0. 1, and E is the elastic modulus. Experimental H-sigma(flow),, data pairs for the large set of alloys are in reasonably good agreement with the mode predictions, but the experimental sigma(flow) are slightly higher and more linearly related to H than predicted. The H-sigma(flow) relation provides insight into the large variation of the H/sigma(y) ratios that are observed for different materials, as well as the corresponding variation in the Delta H/Delta sigma(y) ratios used to estimate Delta sigma(y) due to changes in an alloy's condition, such as that induced by irradiation, based on measurements of Delta H. Notably, combinations of tensile and hardness tests can be use to estimate the average strain hardening from E = 0 to 0. 1 in irradiated alloys that have very small uniform strains. (c) 2007 Elsevier B.V. All rights reserved.