Numerical analysis of plastic deformation evolution into metallic materials during spherical indentation process
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V. Fontanari and B.D. Monellia) Department of Materials Engineering and Industrial Technologies, University of Trento, 38100 Trento, Italy (Received 31 July 2008; accepted 11 December 2008)
The present paper deals with the plastic deformation process into metallic materials occurring in the subindenter region during the loading cycle of spherical indentation test. Load–indentation-depth curve and plastic strains field evolution in the region beneath the indenter are examined using finite element analysis (FEA). The FE model was set up and validated by comparison with experimental spherical indentations carried out on two different materials (Al6082-T6, AISI H13) under four different friction conditions, corresponding to friction coefficients equal to 0.0, 0.1, 0.3, and 0.5. It is confirmed that friction effects on load–indentation-depth curves are negligible for the investigated penetration depths, whereas the plastic deformation process is affected by the contact conditions. The investigation shows that, although the L–h curve is not affected by the contact conditions up to medium values of the penetration depth, remarkable effects are produced in the overall plastic core under the indenter. A strong correlation between plastic strains field and friction coefficient is especially observed at low values of this parameter, whereas a saturation of the phenomena is found for medium-high values of the friction coefficient.
I. INTRODUCTION
In recent years, depth-sensing instrumented indentation testing has become a very attractive method for obtaining mechanical properties of several engineering materials. Indentation tests are nondestructive, inexpensive, and can be applied to obtain local material properties in nonhomogeneous materials. In addition, no specimen has to be extracted from the component to be tested, which can be can relatively small in size. Elastic-plastic properties can be deduced either by sharp1–5 or spherical6–13 indentation. Unfortunately, when adopting the sharp indenters,11,14,15 at least two indentations with different tip angles have to be performed at a certain distance, thus increasing the uncertainties of the results and further complicating the application for nonhomogeneous materials. Spherical indentation that produces crater shapes during the penetration that are not self-similar requires individual tests to obtain the same information. Several procedures based on different approaches have been proposed6–13 to deduce the elastic-plastic properties of the material from the quantities that can be measured during indentations. This indicates that a complete and generally a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0142
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 07 Jan 2015
accepted model connecting material properties and indentation response is not available so far. As pointed out also by Lee et al.10 and Mesarovic and Fleck,16 this is a consequence of the complex evolution of
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