Determination of plastic material properties by analysis of residual imprint geometry of indentation
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A method is presented for the identification of plastic material properties, i.e., yield strength and work hardening rate, using the residual imprint geometry formed by a spheroconical indentation. A corresponding finite element simulation with the same tip geometry and maximum as applied in the indentation experiment yields a numerical imprint profile. Then, the imprint profiles resulting from simulation and experiment are compared, and the material parameters of the simulation are varied by an optimization procedure until a satisfying agreement between simulation and experiment is established. At this stage, the material parameters used for the simulation represent the true material properties. It is shown that this procedure yields unique results that are furthermore verified by independent uniaxial straining experiments. Finally, the reliability of this method with special emphasis on its sensitivity with respect to measurement errors of the imprint geometry is demonstrated. Hence, it is concluded that the residual imprint can be regarded as the fingerprint of a material that contains sufficient information on plastic material behavior to uniquely extract values for yield strength and work hardening rate. I. INTRODUCTION
In material science, indentation testing has a long history and represents an essential method for characterization of various material properties. Among these, determination of elastic properties like Young’s modulus and plastic properties like hardness have been the major and most successful applications of this technique. There are plenty of reasons for the widespread and growing use of indentation techniques: miniaturization in various scientific and technological fields necessitates the quantification of mechanical properties on a scale that has not been as extensively characterized as the macroscopic scale. Furthermore, various sources of size-dependent behavior exist that need to be tested and quantified, yet tensile tests below the millimeter scale pose severe challenges. Indentation techniques in general can be applied to assess local mechanical properties in varying microstructures, e.g., in a welded zone. The preparation and conduction of tensile tests on all scales is a time and costextensive procedure, whereas conventional hardness testing is readily applicable and quasi-non-destructive. However, (nano-)indentation requires a careful and at times tedious specimen preparation as well. As an alternative to conventional materials testing procedures or as a necessity, posed by difficulties in measuring local properties, material characterization by indentation techniques has become a standard method in material a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.212 J. Mater. Res., Vol. 27, No. 16, Aug 28, 2012
science. Nevertheless, the conventional use of indentation techniques is limited to the determination of hardness or microhardness values as strength parameters and does not include the widely used engineering quantities, yield stre
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