DETERMINATION OF MONOTONIC STRESS-STRAIN CURVE OF HARD MATERIALS FROMULTRA-LOW-LOAD INDENTATION TESTS

A method has been proposed to determine the stress-strain curve of har d materials from ultra-low-load indentation tests using geometrically similar indenters. The hardness-flow stress, and characteristic plasti c strain-cone angle correlations, for conical indenters, were obtained from a number of calculations with different stress-strain curves usi ng the finite element code ABAQUS. The flow stress values thus obtaine d, lie between that predicted by the slip line field theory and the sp herical cavity expansion model: These correlations do not assume any d eformation mode, and are thus valid for a wide range of hardness to el astic modulus ratio. The validity of the proposed method was checked b y determining the monotonic stress-strain curve of 1070 steel from ult ra-low-load indentation tests performed in the present study. Also, th e stress-strain curves of copper and steel were obtained from macrosco pic hardness values reported by Atkins and Tabor (Atkins, A.G. and Tab or, D. (1965) Plastic indentation in metals with cones. Journal of the Mechanics and Physics of Solids 13, 149-164.). The predicted stress-s train curves agree well with the known properties of these materials. These correlations were then used to determine the monotonic stress-st rain curve of silicon nitride. (C) 1997 Elsevier Science Ltd.