Characterization of homogenous and plastically graded materials with spherical indentation and inverse analysis
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livier Bartier and Gérard Mauvoisin LaRMAUR—Indentation, Campus de Beaulieu, 35042 Rennes, France
Philippe Pilvin Laboratoire d’Ingénierie des Matériaux de Bretagne, Université de Bretagne-Sud, BP 92116-56321 Lorient Cedex, France
Guillaume Delattre FAURECIA Automotive seating, Le pont de vère, 61100 Caligny, France (Received 5 May 2011; accepted 23 August 2011)
This study investigates spherical indentation of plastically graded materials (PGMs). The hardness of these materials decreases with depth due to microstructural or compositional changes. To predict the behavior of PGM, the knowledge of the plastic properties of the surface and the substrate is necessary. In this work, the spherical indentation technique is applied on carbonitrided steels to obtain their mechanical properties. First, spherical indentation was applied to characterize homogenous materials using inverse analysis. The comparison with tensile test’s results shows that the inverse analysis using spherical indentation data is a reliable method to determine the plastic properties of homogeneous materials. In the second part spherical indentation was used to characterize carbonitrided steels using inverse analysis to obtain plastic properties of the surface. The results show that spherical indentation using inverse analysis has a real potential for evaluating mechanical properties of PGM. I. INTRODUCTION
Surface treatments (carbonitriding, carburizing ...) are highly used in industry since they greatly improve the hardness of the material’s surface. Surface-treated materials have a high hardness on surface and a decreasing hardness profile with depth but have constant elastic properties.1–3 These materials are commonly called plastically graded materials (PGMs). The knowledge of the mechanical properties of PGM is necessary for the prediction of the mechanical behavior of many engineering parts such as gears and rollers. On such materials, a standard tensile test cannot be applied to obtain their mechanical properties. The indentation technique is increasingly used to determine mechanical properties of materials.4–13 This technique can be used to characterize the graded plastic properties of PGM because it characterizes locally the material from only a small volume of material. Moreover, the indentation test needs no or very simple sample preparation. Fewer studies were made on indentation of PGM than on homogenous materials. Two different procedures can be applied to characterize PGM. The first one consists to perform many tests in the section a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.303 20
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
Downloaded: 11 Apr 2015
of the sample.14 The second one consists to make only one indentation test at the surface and then to apply a mixture law.1,3,15–24 Applying the first procedure, Branch et al.14 have recently proposed a method to characterize PGM. They first applied a macro-Vickers indentation on the surface. The
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