Absence of one-to-one correspondence between elastoplastic properties and sharp-indentation load–penetration data

Abstract

The connection between parameters that can be measured by means of instrumented indentation with the real mechanical properties has been a matter of discussion for several years. In fact, even hardness is not a readily measurable magnitude since the real contact area depends on both the elastic and plastic properties of the sample. Recently, Dao et al. [ Acta Mater49, 3899 (2001)] proposed a method based on numerical fittings to calculate by a forward-reverse algorithm the elastoplastic properties of a sample from the load-penetration curve obtained with a sharp indenter. This work will show, in contrast, that it is not possible to measure uniquely these mechanical properties of a sample in that way.

Determination of the mechanical properties of amorphous materials through instrumented nanoindentation

“…1. The main parameters obtained from the test are the maximum indentation load Anax, the maximum indentation depth /* max , and the elastic stiffness upon unloading S. Another interesting factor is the elastic energy/total energy ratio, was demonstrated [3] that only two of these parameters are independent, and thus extra hypotheses are necessary to determine the material properties from a single pyramidal indentation test, as the constitutive behaviour of an elastoplastic solid following the Drucker-Prager model is described by four independent constants (see Section 2.1). This additional information is provided by the characteristic indentation pressure concept, which is presented in Section 2.3.…”

“…An alternative approach is the use of two indenters with different geometry, as suggested for pressure-insensitive materials [3,38]. This approach was proposed by Ganneau et al…”

“…Most of these studies focused on polycrystalline solids, in which the flow stress follows the von Mises criterion and is equivalent under uniaxial tension and compression [1][2][3]. This criterion is not representative, however, of the behaviour of amorphous solids such as ceramic glasses, bulk metallic glasses and both thermoset and thermoplastic polymers.…”

“…Extracting material properties from instrumented indentation is, however, extremely challenging, because there is no one-to-one correspondence between the indentation curve and the material properties [3]. One of the main difficulties in relating both is found in the uncertainty in how the material accommodates the volume displaced by the indenter.…”

Quantitative assessment and prediction of contact area development during spherical tip indentation of glassy polymers

“…Compared to Berkovich indentation, the situation is more complex for spherical indentation as the amount of pile-up is a function of the indentation depth [5]. Some methodologies, alternative to that of Oliver and Pharr, attempt to account for the lack of knowledge of the true contact area in instrumented indentation [6][7][8], in particular for metals. In these approaches, however, the problem is that a single indentation load-displacement curve can have multiple solutions for the mechanical properties, except for special cases.…”