Indentation modulus at macro-scale level measured from Brinell and Vickers indenters by using the primary hardness standard machine at INRiM

Abstract

In this paper, the experimental procedure and calculation model for the measurement of the indentation modulus by using the primary hardness standard machine at INRiM in the macro-scale range at room temperature is described. The indentation modulus is calculated based on the Doerner-Nix linear model and from accurate measurements of indentation load, displacement, contact stiffness, and hardness indentation imaging. Measurements are performed with both pyramidal (Vickers test) and spherical indenters (Brinell test). Test force is provided by a dead-weight machine, and the occurring displacement is measured by a laser-interferometric system. The geometrical dimensions of both the Vickers and Brinell indentations are measured by means of a micro-mechanical system and optical microscopy imaging techniques. Applied force and indentation depth are measured simultaneously, at a 16 Hz sampling rate, and the resultant loading-unloading indentation curve is obtained. Preliminary tests are performed on metal and alloy samples. Considerations and comments on the accuracy of the proposed method and analysis are discussed.

Indentation Modulus, Indentation Work and Creep of Metals and Alloys at the Macro-Scale Level: Experimental Insights into the Use of a Primary Vickers Hardness Standard Machine

“…Although the methods for the evaluation of indentation modulus E IT are widely used, particularly at the micro- and nanoscale levels, and experimental results are often in agreement with the corresponding Young’s modulus, which is not always true at the macroscale level, as can be observed from the experimental results in Table 1 and in [ 43 , 44 ]. At the macro-scale level, the procedure for the calculation of the indentation work is presumably more suitable to properly evaluate the mechanical properties of tested materials, since it was founded with more reliable experimental results that it is independent of contact area A p and is based on a large set of available experimental data; as a consequence, an accurate evaluation of dissipated and stored elastic energy can be useful (beyond the reliability and representativity of large deformations due to high locally applied stresses) to estimate the actual mechanical properties of tested materials, in terms of elastic and plastic behavior and in terms of creep.…”

“…Materials investigated in this paper were copper alloy, aluminum alloy, stainless steel, and copper–chromium–zirconium alloy. Young’s modulus E s and Poisson ratio ν s of the tested materials were previously evaluated from accurate measurements of speeds of sound in solids and in tension at environmental temperature (~21 °C) [ 41 , 42 , 43 , 44 ]. Despite the known systematic difference between dynamic and static moduli, the reference data are accurate as the overall uncertainties are less than 1%.…”

“…To estimate the actual frame compliance in this paper, according to ISO 14755-1 Annex C [ 21 ], a series of loading and unloading cycles, performed on a standardized stainless-steel reference block for hardness (ASAHI HV30) at a single indentation point, was applied. Actually, more procedures are available according to standards and recent literature [ 40 , 44 ], based on the actual indentation depth of Vickers indentation [ 49 , 50 , 51 ].…”

“…Contact stiffness S written as ∂F / ∂h was determined from the Doerner-Nix linear model, by taking into account a portion of 20% of the unloading curve data, as shown in the graph of Figure 2 . The geometrical dimensions of Vickers indentations, such as length l of the indentation side, calculated from the two diagonals d were accurately measured by the optical microscopy imaging technique, as described in detail in [ 44 ].…”