Introduction of the real tip defect of Berkovich indenter to reproduce with FEM nanoindentation test at shallow penetrat
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Leandro Jacomine and Herve Pelletiera) Institut Charles Sadron, CNRS UPR22, F-67034 Strasbourg Cedex2, France (Received 5 May 2011; accepted 29 August 2011)
Indentations tests have been performed on two standard materials SiO2 and Si (100) using two Berkovich indenters presenting different tip defects. Estimations of the tip radii deduced from analyses of maximal applied load versus contact depth and stiffness versus contact depth curves have been compared for experimental observation of each indenter tip obtained with atomic force microscopy (AFM). Results indicate that the determination of the tip defect from data extracted form load–displacement curves is partly dependent on the mechanical properties of the tested material. Then, an original study is proposed to evidence the influence of the tip defect on mechanical response during indentation. Experimental AFM observations of the tip indenter geometries have been introduced in finite element software MSC MARC to reproduce indentation tests on bulk material surfaces. We demonstrated at very shallow penetration depth (less than 50 nm) that the real indenter tip defects have to be considered in the simulation runs, especially to identify accurately the rheological parameters of the tested surface.
I. INTRODUCTION
Nanoindentation is one of the most popular experimental techniques for characterizing the mechanical properties of micro- and nanostructural materials. Since the past two decades, nanoindentation technique participates to the development of new materials, especially thin films that bring significant impacts on technology innovations and rapid growth of microelectronics, biomedical or microelectromechanical systems. An interesting review about nanoindentation measurement technique and its applications can be read in Ref. 1. Depth-sensing indentation method has been developed to continuously monitor penetration depth as a function of applied load during indentation test and then is now currently adopted in the characterization of the mechanical behavior of materials at small scales.2,3 However, the obtained experimental data can provide only the load– displacement curve, and mechanic models are therefore required to convert the test data into the corresponding materials properties.3,4 The accurate determination of mechanical properties, especially at nanometer scale, is directly related to the estimation of the true contact area between the rigid indenter and the deformed surface. The true contact area depends (i) on the estimation of the true contact depth, hc, and then (ii) on the relationship between the contact depth and the real projected contact area, Ac, of the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.387 28
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
Downloaded: 24 Mar 2015
indenter used experimentally, called the indenter area function, Ac 5 f (hc).3 All the mechanic models are usually developed according to certain assumptions, and certain imperfections
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