A study on the determination of plastic properties of metals by instrumented indentation using two sharp indenters

Abstract

An earlier optimisation approach proposed by Luo et al. [Luo, J., Lin, J., Dean, T. A., 2006. A Study on the Determination of Mechanical Properties of a power-law Material by Its Indentation Force-Depth Curve. Philosophical Magazine, 86(19), 2881-2905], which is based on the assumption that the instrumented indentation force-depth response of an elastic-plastic material is a linear combination of the corresponding elastic and elastic-perfect plastic materials, is extended in this work to extract mechanical properties of a power-law material from two given experimental indentation P-h curves for conical indenters of half included angles of 60°and 70.3°. It was found that the non-uniqueness problem encountered in the single P-h curve optimisation approach is effectively removed by the two P-h curves optimisation. The appropriateness of the use of second half included angle of 60°is discussed. For the five representative materials Al, Ti, Fe, Ni and steel, it was found that the maximum relative prediction errors for E, r y and n are 2%, 10.4% and 11.3%, respectively. The prediction accuracy of mechanical properties E, r y and n is generally better than other methods reported in the literature.

Instrumented indentation for determination of full range stress-strain curves

“…The unloading phase can be approximated by Eq. (2) in which B, m and h r are curve fitting parameters [3].…”

Determining elastic–plastic properties from indentation data obtained from finite element simulations and experimental results

“…In recent years, research efforts [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have been focused on extracting elastic-plastic material properties; Young's modulus (E), yield stress (s y ) and work hardening exponent (n), by using indentation data in which a power law hardening is generally used to characterise these material parameters. In previous work, the determination of three properties E, s y and n) and two properties (s y and n) [5,6,8,9,14] have been performed.…”

“…In previous work, the determination of three properties E, s y and n) and two properties (s y and n) [5,6,8,9,14] have been performed. In this work, four elastic-plastic parameters (E, s y , n and Possions's ratio, n) are extracted, for the first time, in a non-linear optimisation approach, fully integrated with FE analysis, using results from a single indentation curve.…”

“…Consequently, some researchers [2,5,9,13] used loaddisplacement curves obtained from more than one indenter geometry (dual indenters) in order to obtain a unique set of material constants. It has been shown that decreasing the indenter angle, i.e.…”

The role of crystalline anisotropy in mechanical property extractions through Berkovich indentation

“…Alternatively, extensive finite element simulations for polycrystalline aggregates performed through the J 2 -flow plasticity theory (assuming isotropic elasticity and isotropic hardening with the Von Mises yield surface), in conjunction with dimensional analyses and contact mechanics formulations, have been used to gain a profound understanding of the relationships between relevant contact variables and mechanical properties (e.g., Refs. [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. These works have led to the development of self-consistent methodologies, where the entire P-h s curve is used to extract yield strength s ys and hardening coefficient n in addition to hardness p and Young's modulus E. The experimental fluctuations in the measurement of the P-h s curves, as well as the large sensitivity of the mechanical properties to slight variations in the contact parameters, however, appear to be the main obstacles in the application of these methodologies.…”