Statistical analysis of the Vickers hardness

The statistical dispersion in Vickers hardness measurements is discussed in order to check the reliability of hardness measurements. Several indentations were made under the same nominal conditions on a hardness standard. This was repeated for different loads. The distribution of diagonal lengths of indentation prints is found to be of Gaussian type. From the distribution function of the indentation lengths, the probability density function of the hardness is derived for the general case of several indentation measurements. The mean value and variance of hardness are compared with results based on Gaussian statistics. From this comparison, it follows that statistical analysis relying upon Gaussian distributions can be carried out within a given confidence level which depends on the number of indentations. A method is presented to calculate the number of indentations needed to achieve a certain level of accuracy.