On the relationships between hardness and the elastic and plastic properties of isotropic power-law hardening materials

Abstract

A comprehensive understanding of the relationship between the hardness and the elastic and plastic properties for a wide range of materials is obtained by analysing the hardness characteristics (that are predicted by experimentally verified indentation analyses) of over 9000 distinct combinations of material properties that represent isotropic, homogeneous, power-law hardening metallic materials. Finite element analysis has been used to develop the indentation algorithms that provide the relationships between the elastic and plastic properties of the indented material and its indentation hardness. Based on computational analysis and virtual testing, the following observations are made. The hardness (H) of a material tends to increase with an increase in the elastic modulus (E), yield strength (σ y ) and the strain-hardening exponent (n). Several materials with different combinations of elastic and plastic properties can exhibit identical true hardness (for a particular indenter geometry/apex angle). In general, combinations of materials that exhibit relatively low elastic modulus and high yield strength or strain-hardening exponents and those that exhibit relatively high elastic modulus and low yield strength or strain-hardening exponents exhibit similar hardness properties. Depending on the strainhardening characteristics of the indented material, (i.e. n = 0 or n -0), the ratio H/σ y ranges, respectively, from 2.2 to 2.6 or 2 to 20 (for indentations with a cone angle of 70.3°). The materials that have lower σ y /E and higher n exhibit higher H/σ y ratios. The commonly invoked relationship between hardness and the yield strength, i.e. H ≈ 3σ y , is not generally valid or applicable for all power-law hardening materials. The indentation hardness of a power law hardening material can be taken as following the relationship H ≈ (2.1-2.8)σ r where σ r is the representative stress based on Tabor's representative strain for a wide range of materials.

Nanoindentation study of electrodeposited Ag thin coating: An inverse calculation of anisotropic elastic-plastic properties

“…So the contact areas were calibrated carefully before indenting on different materials to minimize these effects. The different hardness values along the two directions clearly indicate the existence of anisotropy in the current coating since hardness values are dominant by the plastic properties [50]. In addition, no hardness gradient is measured through the coating thickness among the various indents in the T direction shown in Figure 1(e), which indicate that the hardness values of the Ag coating near the free surface are close to those near the Ag-Ni interface.…”

White layer formation mechanism in dry turning hardened steel

“…Moreover, the white layer thickness increases with the material hardness. With the increase of the Duan, Zhang, Sun, Xu and Wang, Journal of Advanced Mechanical Design, Systems, and Manufacturing, Vol.12, No.2 (2018) material hardness, the plastic resistance of the cutting process and the friction resistance between the tool and the machined surface increase (Lan and Venkatesh, 2014), so the energy that is consumed in the cutting process increases. When the hardness of workpiece is low, the cutting temperature which is transferred by the consumed energy cannot reach to the austenite transformation temperature, so although the severe plastic deformation occurs in machined surface, there is no white layer, which verifies that the white layer is formed by phase transformation primarily and the plastic deformation can promote white layer formation process.…”

Influence of Prosopis Juliflora wood flour in Poly Lactic Acid – Developing a novel Bio-Wood Plastic Composite

“…Increase in fiber content had a reduced pattern on hardness values, the C1 and F1 composite had the highest hardness while C4 and F4 composite had the lowest hardness value within their categories. This factor is in contradiction with the fact that hardness increses with increase in elastic modulus [29] . The observed reduction in hardness can only be assumed that the nature of PJ, since every wood fiber has its own distinctive property [30] .…”