Proposal for a practical procedure for the expression of uncertainty in hardness measurements

Hardness measurement is widely used in industrial applications for quality control and acceptance testing of products because it is fast, inexpensive and relatively non-destructive. Uncertainty evaluation is complicated because calibration procedures require the use of direct and indirect verification tests, but the effects on the measurand itself due to test parameters variations are difficult to predict, such as the force-time pattern, inelastic performances of Rockwell indenters and the numerical aperture for Brinell and Vickers indentations measurement. This paper starts by accepting as a matter of fact that standard specifications have demonstrated acceptable performance, indicating that their application is correct for most of the materials generally used. Accepting this premise, the next step was to try to translate the practice, confirmed by many years of experience, into the new language of uncertainty, strongly required by quality documents.