Characterization of structural materials by spherical indentation

Abstract

Nano-indentation with spherical indenters is a method of mechanical properties characterization that could be used for the determination of stress-strain curves. A necessary condition for an evaluation of the results is an exact knowledge of the indenter shape. In this study, the shapes of two spherical indenters with a nominal radius of 20 μm were investigated by atomic force microscopy and by indentation into materials with a known Young's modulus. It was found that the actual indenter differs from the ideal shape and it is affected by the crystallographic orientation of the diamond crystal. The effective radius determined from the indentation measurements depends on the material deformation characteristics and it was lower than the actual radius. The computed representative stress vs. representative strain curves of steel samples were significantly affected by the actual radii of the investigated indenters.