Two definitions of the newer HPV hardness measure as a volumetric modification of the Brinell measure

Abstract The Brinell ball hardness test is based on a measure of the total surface area of the indentation or a measure of the depth of the indentation. Although the Brinell hardness test is well-established, none of its basic measures has sufficient physical justification. Consequently, the Brinell hardness measure in the experiment depends on the load value, with a maximum for half-diameter indentations and a minimum for full indentations. Therefore, a slightly different hardness measure for the ball test has been proposed, which is based on the volume of the indentation and, at the same time, has an energetic justification. The newer hardness measure has been abbreviated as HPV, from the words Hardness-Pressure-Volume, which best reflects the essence of this measure. Two equivalent definitions of the HPV measure have been given. The first geometric definition relates the volume of a real indentation to the indentation volume of an ideal parabolic indenter. The second energetic definition is based on the average volume work of deformation of the material resisting hardness, in terms of pressure (stress). The preliminary experimental result showed that the HPV hardness measure is characterised by a lower correlation with the loading force than the Brinell measure on the transverse section of linden wood. This result reached a level of statistical significance of 0.03.