Relation between strain hardening exponent of metals and residual profiles of deep spherical indentation

Strain hardening exponent is an important mechanical property usually obtained from tensile tests, which implies that a specific specimen preparation and long routines of calculus should be performed. An alternative way to obtain this property is the use of spherical indentation hardness, measuring the profiles of indentation morphology: piling up or sinking in. In the present investigation, the indentation morphologies observed after tests with a spherical indenter for aluminium alloys (AA 6063-T5 and AA 1350) and steels (AISI 1020 and AISI 316L) are presented. Indentation tests were performed with different sphere diameters and test loads, to obey the Meyer law and to keep constant the relation between load and indentation diameter, varying the plastic strain level. Tensile tests were performed to make use of reference values. The residual profiles were obtained using a two-dimensional profilometer. The results allow discussing the range of validity of several models proposed in the literature. For some test conditions, 316L stainless steel and 1350 aluminium alloy partially recovered present an unexpected behaviour, which the models are unable to predict.