Representative Strain of Indentation Analysis

Abstract

Indentation analysis based on the concept of representative strain offers an effective way of obtaining mechanical properties, especially work-hardening behavior of metals, from reverse analysis of indentation load-displacement data, and does not require measuring of the projected contact area. The definition of representative strain adopted in previous studies [e.g., Dao et al., Acta Mater. 49, 3899 (2001)] has a weak physical basis, and it works only for a limited range in some sense of engineering materials. A new indentation stress-state based formulation of representation is proposed in this study, which is defined as the plastic strain during equi-biaxial loading. Extensive numerical analysis based on the finite element method has shown that with the new formulation of representative strain and representative stress, the critical normalized relationship between load and material parameters is essentially independent of the work-hardening exponent for all engineering materials, and the results also hold for three distinct indenter angles. The new technique is used for four materials with mechanical properties outside the applicable regime of previous studies, and the reverse analysis has validated the present analysis. The new formulation based on indentation stress-state based definition of representative strain has the potential to quickly and effectively measure the mechanical properties of essentially all engineering materials as long as their constitutive behavior can be approximated into a power-law form.

Application of spherical nanoindentation to determine the pressure of cavitation impacts from pitting tests

“…Since that work, a number of studies have attempted to describe indentation stress-strain curves with some promising success. [22][23][24][25][26][27][28][29] In this work, we propose to use depth-sensing indentation techniques to calibrate the impact pressure due to bubble collapses by adopting the material itself as a sensor, which is able to detect the impact loads. To achieve this goal, indentation experiments with a spheroconical diamond tip were performed on a nickel-aluminum-bronze alloy and analytical procedures were developed to extract stress-strain curves from indentation loading-unloading data; experimental pitting tests were performed in a cavitation tunnel at four different operating pressures, and a conventional contact profilometer was adopted to measure the main geometrical characteristics (depth, surface, and volume) of the erosion pits; and finally, the coupling of the analysis of pitting tests with the material information obtained via the indentation tests allowed the evaluation of the pressure of cavitation impacts and its statistical distribution, thereby quantifying the hydrodynamic aggressiveness of the cavitating flow.…”

Effect of dynamic strain rate on micro-indentation properties of pure aluminum

“…Dao et al [9] introduced the concept of the representative strain, which is used for the indentation analysis to normalize the load-displacement curves of the indentation. The authors [10] proposed more exact the representative strain as follows:…”

Erratum: “Representative strain of indentation analysis” [J. Mater. Res. 20, 2225 (2005)] and “Limit analysis-based approach to determine the material plastic properties with conical indentation” [J. Mater. Res. 21, 947 (2006)]

“…1,2 A typographical error of a number appeared in Fig. 5 these two figures are the same schematic drawing.…”