Mechanical property evaluation through sharp indentations in elastoplastic and fully plastic contact regimes
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ollowing the finite element simulations in our earlier work about the contact deformation regimes, mathematical formulations were derived to correlate hardness and the amount of pileup and sinking-in phenomena around sharp indenters with uniaxial mechanical properties. The formulations are applicable regardless of the deformation regime ruling the contact response of a strain-hardening solid. A methodology was devised where the use of these formulations in mechanical property assessments from indentation experiments was demonstrated. The current results make contact with existing methodologies using the II-theorem in functional analysis to extract uniaxial properties from instrumented indentation load depth of penetration curves. It is argued that since surface deformation is an essential feature of the contact response, it enters directly or indirectly in such existing methodologies. The paper considers how independent knowledge of surface deformation can be used to guide mechanical property assessments from load-depth of penetration curves. A discussion on the uniqueness of mechanical characterizations through indentation experiments is also provided. I. INTRODUCTION
The contact response of a material is conventionally evaluated through hardness measurements and with assessments of surface deformation effects (i.e., the amount of pileup and sinking-in induced at the contact boundary).1–3 With the advent of instrumented indentation techniques, research has been devoted to evaluating uniaxial mechanical properties from load (P)-depth of penetration (hs) curves, circumventing the need to perform direct measurements of the imprint size which require the use of sophisticated tools, especially in nanoindentation.4–17 [The depth of penetration measured by instrumented indentation is denoted as hs throughout this article, where subscript s refers to the distance from the original (undeformed) surface of the material to the indenter’s tip; i.e., disregarding surface deformation effects (Fig. 1 in Refs. 1 and 18)]. A significant amount of the research conducted along these lines focuses in the use of the II-theorem in dimensional analysis to evaluate mechanical properties through P-hs curves.6–9,13–15 In the past few years, however, commercial stand-alone nanoindenters have been equipped with atomic force microscopes (AFMs) to obtain detailed evaluations of the imprint’s topography. In addition, conventional stylus a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 7, Jul 2003
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profilometry is available to perform such topographical assessments in the micro- and macroindentation ranges. In view of the widespread use of AFM techniques, it now seems worthy to develop methodologies explicitly using surface deformation assessments and hardness to extract uniaxial mechanical properties.1,18–20 Motivated by our findings on the contact deformation regimes around a conical indenter with included halfapex angle of 70.3°,1 the
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