NEW ANALYTICAL PROCEDURE TO DETERMINE STRESS-STRAIN CURVE FROM SPHERICAL INDENTATION DATA

Spherical-indentation process was analyzed by finite element (FE) meth od. A systematic analysis of relationship between indentation paramete rs and true stress/plastic-strain (sigma(t)-epsilon(p)) curve was perf ormed for a range of material properties. An existing method relates t he ratio or residual contact diameter, d, and indenter diameter, D, to epsilon(p) by the well-known Tabor's empirical equation epsilon(p) = 0.2d/D. The method is based on parameters of residual indentation, whe re a loading-unloading cycle needs to be made in order to calculate a point on sigma(t)-epsilon(p) curve. A new analytical approach is prese nted which relates the indentation data continuously measured during l oading to sigma(t)-epsilon(p) curve. epsilon(p) calculated by the new method is in the range from yield strain to a strain between 0.3 and 1 .6, depending on material's strain hardening properties. In addition, different measures of indentation diameter are discussed and their inf luence on the resulting sigma(t)-epsilon(p) curve analyzed. Experiment al work was performed by an instrumented spherical-indentation techniq ue in order to verify the FE analysis results. A good agreement betwee n the FE and experimental results was obtained. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.