Material hardness - Influence of elasticity

Elasticity plays a significant and often overlooked role in hardness testing, particularly with spherical indenters, and in tests to monitor the evolution of force with penetration, usually carried out on the nanometric scale. We first review the theory of elastic indentation and its application to the study of the discharge curve in nanoindentation tests on homogeneous and coated materials. We then analyse elastoplastic indentation, first by recalling the approximate but simple model of the expanding cavity, and then by presenting the results of finite element analyses in the case of spherical indenters, where the influence of elasticity decreases continuously for increasing forces, and conical indenters, where elasticity retains a non-negligible influence, notably on contact geometry.

This article is part of a series on hardness testing:

• Body hardness and qualitative analysis [M 4 154] ;

• Hardness of common metals. Rigid-plastic limit case [M 4 155] ;

• Hardness of materials. Influence of elasticity [M 4 156] ;

• Hardness of bodies. Analysis of other behavior [M 4 157] ;

• Find out more [Doc. M 4 158].

Most of the symbols used in this article have already been introduced in [M 4 154]. Readers may find it useful to refer to their table of symbols.