The uncertainty of hardness measurements related to the measurement method, surface preparation and range of the measurements

Abstract

The main purpose of this paper is to present the changes in hardness-measurement uncertainty depending on the measurement method, the number of measurements and the surface preparation. The experiments were executed on the AlCuMgPb aluminium alloy series 2xxx, manufactured from one batch of homogenous material. The measurements were performed on milled and polished surfaces using different hardness-test methods: Brinell, Vickers and Rockwell. The goal of this study was to select the optimum hardness test method together with the surface preparation that provide the best results in terms of measurement uncertainty. Finally, the results including the effect of the number of performed measurements for different surface preparations were presented. The statistical deviation in the hardness-measurement results showed a lowest scatter of measured results for the Rockwell method and the largest for the Brinell test. It was also concluded that the repeatability increased when surface of the sample was polished, simultaneously only three measurements were needed, using the Brinell and Rockwell methods, to achieve the minimum required error parameters.