Analysis and estimation of possible large systematic error in Brinell hardness measurements

Brinell hardness measurements are widely used at industrial level. For the calculation of Brinell hardness values, the measurement of the diameter of indentations is necessary. In practice, the measurement of the image created by the optical systems used for the magnification of the indentation is usually carried out. The dimension of the indentation image depends by the optical system that, in practice, transform the real indentation in image using properties of light reflection. The paper describe the effect of this influence parameter in Brinell hardness measurements in experiments carried out at hardness laboratory of Istituto Nazionale di Ricerca Metrologica (INRIM) (formerly Istituto di Metrologia “G. Colonnetti” – IMGC) with application to the data obtained at international comparison at the National Metrology Institutes level. Moreover, some methods for its evaluation and possible correction will be proposed.