Elastic properties determination from indentation tests

The knowledge of mechanical properties, and elastic modulus in particular, is necessary for a good understanding of the behaviour of materials subjected to static or dynamic loading. Accurate determination of elastic modulus is possible in the case of massive and homogeneous materials. For coatings the problem is more complicated but this determination is rendered possible using load and displacement sensing indentation tests or ultrasonic wave tests, for example. The purpose of this study is to determine elastic modulus of materials and specially that of coatings by analysing the morphology of indents obtained by the Vickers hardness test. During the withdrawal of the indenter, distortions of the faces of the indent are directly linked to the elastic properties of the material. Comparison between the true volume of the deformed indent and the ideal volume of the Vickers pyramid allows one, starting with Bulychev's relation, to achieve good estimations of the elastic modulus of massive materials as well as that of coatings. The model is first tested on massive material of known elastic properties (middle carbon steel, ferritic stainless steel and aluminium alloy), then it is applied to a chromium carbide coating obtained by hypersonic thermal spraying. Calculated elastic moduli are in accordance with literature data, except for the aluminium alloy, for which plastic flow around the indent is different from the other materials.