Finite element analysis of spherical indentation to study pile-up/sink-in phenomena in steels and experimental validation

The ball indentation technique based on deforming a material with a spherical indenter is an useful non-destructive tool for evaluating mechanical properties from a very small volume of material. In this work, the indentation test carried out using a 1.0 mm diameter tungsten carbide ball to penetration depths of around 100-200 mu m is modeled using finite element (FE) method and analyzed for three steels having different yield stress and strain hardening exponent. The FE generated load-depth curve is compared and verified with the experimental load-depth data for the three materials. The role of the contact friction at the indenter-specimen interface on both the load-depth plot and indentation profile are examined. The development of pile-up/sink-in during indentation and its dependence on strain hardening characteristics of the material, contact friction and indentation depth are analyzed using the FE model. The indentation profiles obtained from simulation are compared with experimental profiles and the implication of pile-up phenomenon on accurate evaluation of stress-strain values from the experimental indentation load-depth data is discussed. (C) 2011 Elsevier Ltd. All rights reserved.