Identification of viscoplastic material parameters from spherical indentation data: Part II. Experimental validation of
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. Tyulyukovskiy and N. Huber Forschungszentrum Karlsruhe, Institut für Materialforschung II, 76021 Karlsruhe, Germany (Received 23 August 2005; accepted 22 November 2005)
A neural network-based analysis method for the identification of a viscoplasticity model from spherical indentation data, developed in the first part of this work [J. Mater. Res. 21, 664 (2006)], was applied for different metallic materials. Besides the comparison of typical parameters like Young’s modulus and yield stress with values from tensile experiments, the uncertainties in the identified material parameters representing modulus, hardening behavior, and viscosity were investigated in relation to different sources. Variations in the indentation position, tip radius, force application rate, and surface preparation were considered. The extensive experimental validation showed that the applied neural networks are very robust and show small variation coefficients, especially regarding the important parameters of Young’s modulus and yield stress. On the other hand, important requirements were quantified, which included a very good spherical indenter geometry and good surface preparation to obtain reliable results.
I. INTRODUCTION
The investigation of mechanical properties of small volumes by means of nanoindentation is of growing importance. While the recent development in micro- and nano-applications tend towards imaging of topography and scanning of mechanical properties over comparable large areas or cross sections using the same indenter tip, an interesting development in the macro range can be observed. New machines, like the Zwick hardness tester (Zwick/Roell), are designed to measure hardness with depth and force reading systems at higher force regimes and with larger tip radii compared to the common nanoindenter systems. Thus, analysis techniques can be applied to macro experiments as well, whose development was originally pushed by nanoindenter systems. On the other hand, there is a useful tradition of verifying new analysis techniques by macro experiments.1–5 In this way, common difficulties with nanoindenters, like surface effects due to polishing, zero point correction problems due to surface roughness, and systematic errors from imperfect tip shapes can be reduced to a minimum with comparable small effort.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0077 J. Mater. Res., Vol. 21, No. 3, Mar 2006
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The motivation of the present paper is caused by both reasons mentioned above. On the one hand, it uses macroindentation experiments to verify the proposed analysis methods developed in the first part.6 On the other hand, there is a great interest in providing new analysis techniques for macroindentation devices and to include them in current discussions on the future extension of the ISO standard.7 After the first part of the paper6 deals with the constitutive equation of the material and the identification of the materials para
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