Indentation instrumentée multi-échelles appliquée à l’étude des matériaux massifs métalliques

Abstract

Résumé -L'essai d'indentation instrumentée est une technique très utilisée car elle permet d'estimer les propriétés mécaniques des matériaux comme la dureté et le module de Young. Cetteétude sur l'indentation multi-échelles (de 5 mNà 2 kN) aété réalisée sur des matériaux métalliques massifs (acier, acier inoxydable et aluminium) avec trois instruments : nano, micro et macro indenteurs, et différents types d'essais : classique, CSM et multicyclique. Nous avons constaté que, pour estimer les propriétés mécaniques, il est nécessaire de prendre en compte la correction du défaut de pointe et aussi de la complaisance du bâti quelle que soit l'échelle de mesure, et donc quelle que soit la conception de l'instrument pour la mesure du déplacement. Dans ces conditions, en considérant ces corrections, le module de Young reste quasi constant dans tout le domaine de forceétudié (<12 %), et est doncà ce titre une propriété intrinsèque. Par contre, la dureté décroit lorsque la charge augmente, ce qui est classiquement attribuéà l'effet de taille en indentation, mais qui peut aussiêtre imputé au mode de déformation autour de l'empreinte, au bourrelet prédominant (pile-up) pour leséchantillons en acier et aluminium, età la déflection des faces (sink-in) pour l'acier inoxydable. Mots clés : Indentation multi-échelles / module de Young / dureté / modes de déformationAbstract -Instrumented multiscale indentation applied to the study of bulk metallic materials. The instrumented indentation test (ITT) is a largely used technique, because it allows to estimate the mechanical properties of materials, as hardness and Young's modulus. This study about multi-scale ITT (from 5 mN to 2 kN) was performed on bulk metallic materials (steel, stainless steel and aluminum) using three instruments: nano, micro and macro indenter, and different kinds of test: standard, CSM and multicycle. We have found that for the estimation of the mechanical properties, it is necessary to consider the correction of the frame compliance and tip defect, for all the scales of measurement and instruments. In these conditions, considering these corrections, the Young's modulus is almost constant among all the range of studied loads (<12%), being an intrinsic property. On the contrary, the hardness decreases while increasing the load, which is typically attributed to the indentation size effect, but also it can be related to the deformation around the imprint, pile-up for the samples of steel and aluminum, and sink-in for the stainless steel.

Spin crossover molecular ceramics by Cool-SPS: consequences on switching features beyond microstructural effects

“…It was suggested that this microstructural fatigability was accompanied by a subtle structural variation corresponding to a slight rotation of the chain linked to the decrease of the a parameter. 67 Since a similar evolution of the a parameter is also detected on ceramics in addition to the reduction of the coherent domain size in the b direction, it seems that the sintering process leads to a very similar microstructural and structural evolution, but without cycling.…”

Study of mechanical performance of polymer nanocomposites reinforced with exfoliated graphite of different mesh sizes using micro-indentation

“…Elasticity and fracture toughness can also be calculated from the forcedisplacement curves recorded. This technique allows studying the mechanical properties of materials at different scales [34]. ¶…”

“…This technique allows studying the mechanical properties of materials at different scales. 34 The specific indication that we faced with the microindentation test is the indentation depths, which are, Figure 7: h t is the whole depth below a load P t , h e is the elastic rebound depth for the unloading duration, h f is the depth of the residual impression, h a is the surface displacement at the perimeter, h p is the depth of the contact indentation.…”