Effect of contact stiffness and machine calibration in nano-indentation testing

Instrumented indentation tests enable evaluation of several material parameters. Preliminary investigations underlined the influence of contact stiffness in the nano-range. ISO 14577-1 recommends two methods for contact stiffness evaluation, which, however, present shortcomings mainly related to the disregard of actual shape of unloading indentation curve. Given the relevance not only at the extent of material characterization, but also at testing machine calibration, alternative evaluation procedures have been developed, showing better agreement with experimental data and lower uncertainty in the evaluation of contact stiffness. In this work, shortcomings of standard and alternative methods in the evaluation of material parameters are highlighted, and innovative procedures are proposed to overcome them.