An analysis of load–penetration curves from instrumented indentation Original Research Article

A new empirical method is proposed for analyzing nano-indentation load–displacement curves. This method is based on experimental results and finite element (FEM) calculations reported in the literature. This method proposes to link the indentation–unloading curve to elastic modulus and strain-hardening properties. Through the analysis, elastic modulus, yielding stress and strain hardening properties are derived from the complete indentation load–displacement curve. This new method has then applied to the nano-indentation experiments of 14 different materials in which the elastic modulus ranges from 3 to 650 GPa and the hardness ranges from 0.1 to over 30 GPa. The elastic modulus, hardness and yielding stress derived from the new method agreed well with the literature values. An analysis of the loading curve also shows that there is a transition region, in which of the exponent of the loading curve changes from 1.5 to 2 corresponding to the change of the loads from low to high. This implicates that to avoid this transition region in loading curve, one should keep the load of the nano-indentation larger than approx. 30 mN.