L’essai de dureté Vickers : Application et influence de la charge

Abstract

Indentation hardness testing is probably the most simple technique use to provide the mechanical characteristics of a materials. In first, different types of hardness are presented with there applications in fonction of range hardness. Vickers test is the one in most widespread used but for applied load less than 100 gf, it is experimentally well established that the apparent micro-hardness varies with applied load and this effect is known as the “Indentation Size Effect” (I.S.E.). This variation of the hardness with applied load was first compared with various existing models and the surface profile, near the indentation print, was measured by confocal microscopy. This measures shows a formation of a budge around the indentation print and so the real indentation surface can’t be obtained by the simple measurement of the contact surface. A model was developped for the geometry of budge and the real surface of contact between the indenter and the specimen was calculated by the length of the diagonal print and the width budge. For two materials investigated (TA6V titanium alloy and 2024 - T3 aluminium alloy), the I.S.E. effect is an artefact i.e. the variation of hardness with the applied load is only a consequence of the variation of the appeared contact surface between the specimen and the indenter. So, we show that I.S.E. allows to determinate others properties of samples such Young’s modulus, fatigue behaviour, or more residual stresses in materials, tenacity ....