An energy-based method to extract plastic properties of metal materials from conical indentation tests

Abstract

Based on dimensional analysis and finite element computations, an energy-based representative strain for conical indentation in elastoplastic materials has been proposed to establish an explicitly one-to-one relationship between the representative stress σr, the indentation loading curvature C, and the ratio of reversible work We to total work Wt performed by the indenter, i.e., σr/C = F0(We/Wt), where σr is the flow stress corresponding to the representative strain. The relationship provides a very simple method to evaluate the representative stress σr from the three directly measurable quantities We, Wt, and C. Numerical examples and further theoretical analysis reveal that a unique, stable solution can be obtained from the present method for a wide range of material properties, including both highly plastic materials (e.g., Ni for which E/σy = 1070) and highly elastic materials (e.g., materials for which E/σy = 25 and n = 0.5), using indenters with different tip apex angles. Based on the representative strains and stresses given by two indenters with different tip apex angles, e.g., (σr,80, ϵr,80) and (σr,65, ϵr,65), the plastic properties of materials, i.e., the yield strength σy and strain hardening exponent n can be further determined.

A precise correcting method for the study of the superhard material using nanoindentation tests

“…The error between the contact area from Eq. (15) and that directly obtained from the finite element simulation is 3.7%. In a recent article, Fischer-Cripps et al 24 performed an interesting experiment by indenting a diamond indenter into an industrial diamond substrate.…”

“…To further examine the accuracy of Eq. (15) in the case that the sink-in of the substrate is more significant, we simulated the diamond indenter indenting into a material for which the Poisson's ratio is ‫ס‬ 0.0, the Young's modulus is E ‫ס‬ 800 GPa, and the yield strength is y ‫ס‬ 100 GPa. In this case, the h c /h t ratio is 0.66.…”

“…2 It is also possible to use indentation tests to determine the stress-strain curves of elastoplastic materials. [3][4][5][6][7][8][9][10][11][12][13][14][15] Besides being used on bulk materials, indentation tests can be used to probe the mechanical properties of thin films and coating systems. 16,17 The present research is relevant for the analysis of the conical indentation into an elastic half-space, which is useful when taking at least the following two aspects into consideration.…”

Evaluation of the effectiveness of representative methods for determining Young's modulus and hardness from instrumented indentation data

“…Finally, it should be pointed out that there have been new attempts in developing techniques for investigating accurate plastic properties of materials. 23,24 One approach is to use two conical indenters of different halfincluded angles to perform depth-sensing indentation tests. Results may help to extract the yield stress and hardening behavior of the indented material.…”

Revelation of a functional dependence of the sum of two uniaxial strengths/hardness on elastic work/total work of indentation

“…Therefore, more recently, a new approach has been developed: using two conical indenters of different half included angles to produce independent load-displacement curves for deriving material properties like yield stress and hardening coefficient etc. [9][10][11][12] In fact, more work is still required to examine the effectiveness and possible error of the method.…”