Instrumented indentation test: Contact stiffness evaluation in the nano-range

Instrumented indentation test is a non-conventional hardness test, relevant for both performing hardness measurement and estimating the elastic modulus. The indentation modulus, which depends on the contact stiffness, estimates the elastic modulus. To evaluate contact stiffness, literature requires to fit force-displacement curve according to mathematical models, which are hardly representative of the curve. This research aims at proposing alternatives, which estimate contact stiffness directly from experimental data. Proposed methods are applied to nano-indentations performed on a reference material and a high-speed bearing steel; indentation modulus is evaluated along with uncertainty contribution of contact stiffness. Comparison with standard methods is provided.