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G.M. Pharrb) University of Tennessee, College of Engineering, Department of Materials Science and Engineering, Knoxville, Tennessee 37996-2200; and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6132 (Received 30 June 2008; accepted 15 September 2008)

The purpose of this work is to further develop experimental methodologies using flat punch nanoindentation to measure the constitutive behavior of viscoelastic solids in the frequency and time domain. The reference material used in this investigation is highly plasticized polyvinylchloride (PVC) with a glass transition temperature of
17  C. The nanoindentation experiments were conducted using a 983-mm-diameter flat punch. For comparative purposes, the storage and loss modulus obtained by nanoindentation with a 103-mm-diameter flat punch and dynamic mechanical analysis are also presented. Over the frequency range of 0.01–50 Hz, the storage and loss modulus measured using nanoindentation and uniaxial compression is shown to be in excellent agreement. The creep compliance function measured using a constant stress test performed in uniaxial compression and flat punch nanoindentation is also shown to correlate well over nearly 4 decades in time. In addition, the creep compliance function predicted from nanoindentation data acquired in the frequency domain is shown to correlate strongly with the creep compliance function measured in the time domain. Time–temperature superposition of nanoindentation data taken at 5, 10, 15, and 22  C shows the sample is not thermorheologically simple, and thus the technique cannot be used to expand the mechanical characterization of this material. Collectively, these results clearly demonstrate the ability of flat punch nanoindentation to accurately and precisely determine the constitutive behavior of viscoelastic solids in the time and frequency domain.

I. INTRODUCTION

Nanoindentation experiments are attractive because they provide the opportunity to characterize a wide range of materials with spatial resolutions in the nanometer to micrometer range. However, contact experiments introduce additional complexity in interpreting experimental data because the state of stress and strain in the volume of material being sampled is not uniform. While the instrumentation is capable of performing experiments at small length scales (tens of nanometers in contact size), the relationship between the measured quantities such as load, displacement, and stiffness, to a)

Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr_policy DOI: 10.1557/JMR.2009.0089 626

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J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 16 Feb 2015

the constitutive behavior of the sample is seldom clear, even from contact dimensions in the micrometer range. Only b