INFLUENCE OF DIFFERENT NUMERICAL APERTURES ON HARDNESS VALUES USING AN AUTOMATIC SYSTEM OF MEASUREMENT

Renato R. Machado, Sérgio P. de Oliveira, Claudio A. Koch, Islei D. da Silva, Bianca da C. O. Muniz

Abstract

The objective of this work is to analyse and discuss the influence of the use of different numerical apertures (NA) and its magnification on the measurement of indentations on Vickers (HV) and Brinell (HB) hardness blocks previously certified. It was used a new reference Vickers and Brinell measurement system, recently installed and qualified at the Brazilian National Metrology Institute (Inmetro) by the National Institute of Metrological Research (iNRiM/Italy). The system used was a Galileo Galvision (LTF S.p.A., Italy) that carries out automatic measurements throughout two methods, the direct and the indirect ones. In the present work both direct and indirect methods were used. In general, the 10x lens magnification and its 0,25 numerical aperture yielded the acceptable normalized error (En) for almost all HV and HB indentation measurements done, no matter the method used. As reference values six certified blocks in three levels of hardness were studied, e.g. blocks of low, medium and high hardness values. Among them, the lowest range of Vickers hardness provided the better normalized error. The same results were obtained by analyzing the highest range of Brinell hardness, no matter the method used.

Keywords

Hardness, Indentation, Numerical Aperture

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IMEKO-TC5-2007-012.pdf

DOI

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IMEKO TC

TC5 - Hardness Measurement

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