Mechanical tensile properties by spherical macroindentation using an indentation strain-hardening exponent
Résumé
The determination of the tensile properties by spherical indentation is based on the relation of Tabor, which links the mean pressure and the indent diameter, obtained from indentation tests, to the stress and strain determined from a tensile test, respectively. However, in order to improve the indentation-tensile relationship, an additional correction related to the piling-up or sinking-in formation around the indent must be taken into account for the calculation of the strain by indentation. The correction factor is expressed as a function of the strain-hardening exponent. As a consequence, to validate such methodology, majority of the authors use the strain-hardening exponent previously determined by a tensile test. Unfortunately, this approach obviously impedes a direct construction of the tensile curve from indentation tests since the strain-hardening exponent will be undetermined. In addition, the tensile stress to mean pressure ratio is not a constant value because it depends on the mechanical properties and on the deformation regime. To circumvent these two problems, a simple expression of the mean pressure to stress ratio is proposed in macroindentation as a function of the strain-hardening exponent, which is determined by indentation tests using the relations of Hollomon and Ramberg-Osgood. This methodology, which allows the construction of the stress -strain curve only from indentation tests, is validated on a low-carbon steel and a commercial brass.