Hardness, Modulus, and Thickness

Abstract

Abstract Series expansions are used to show that a simpler, more practical formula can be adopted to replace previous expressions of correlation between international degrees of hardness and shear moduli. This formula also appears to be nearer to the one deduced from the theory for the Shore durometer. General application is also given to a law relating these factors to the thickness of the test strips, which law has been previously found applicable to indenter hysteresimeters. This formula, which could probably also be used with other instruments with differently shaped indenters, has been particularly carefully checked for the ISO durometer with a ball indenter, and agrees excellently with experimental data. The mathematical relation, which has a single parameter, probably related only to shape and size of the indenter, allows the definition of an exponential parameter which generalizes the use of Scott's formula to smaller thicknesses. Finally, combination of the two new expressions makes it possible to put the dependence of degrees of hardness on thickness into a general form.