A procedure to prevent pile up effects on the analysis of spherical indentation data in elastic–plastic materials

Indentation tests are commonly applied to determine surface mechanical properties of very different kind of materials. In many circumstances, results provided by indentation are different to those obtain by more traditional tests (tensile, compression, etc.). In the particular case of elastic–plastic solids, phenomena like pile up or sink in cause deviations in Young’s modulus and hardness data if any correction procedure is applied to the experimental load–displacement curves. In this work, a finite element model was used to evaluate the pile up and sink in effects on the determination of mechanical properties in a wide range of elastic–plastic materials. Several combinations of Young’s modulus, yield stress and hardening exponent were considered. Taking into account the non-geometrical similarity of spherical tips, this configuration was chosen to suggest a new procedure, based on a combination of results obtained from tests performed at multiple maximum loads. The method gives consistent results and it was experimentally validated comparing nano-indentation and tensile tests of bulk metallic materials.