Development of an Advanced Dynamic Microindentation System to Determine Local Viscoelastic Properties of Polymers

Esther Ramakers-Van Dorp,Berenika Hausnerova,Thomas Haenel,Bernhard Möginger,Dominik Ciongwa

doi:10.3390/polym11050833

Esther Ramakers-Van Dorp, Berenika Hausnerova + Show 3 more

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https://doi.org/10.3390/polym11050833

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Abstract

This study presents a microindentation system which allows spatially resolved local as well as bulk viscoelastic material information to be obtained within one instrument. The microindentation method was merged with dynamic mechanical analysis (DMA) for a tungsten cone indenter. Three tungsten cone indenters were investigated: tungsten electrode, tungsten electrode + 2% lanthanum, and tungsten electrode + rare earth elements. Only the tungsten electrode + 2% lanthanum indenter showed the sinusoidal response, and its geometry remained unaffected by the repeated indentations. Complex moduli obtained from dynamic microindentation for high-density polyethylene, polybutylene terephthalate, polycarbonate, and thermoplastic polyurethane are in agreement with the literature. Additionally, by implementing a specially developed x-y-stage, this study showed that dynamic microindentation with a tungsten cone indenter was an adequate method to determine spatially resolved local viscoelastic surface properties.

Highlights

Micro- and nanoindentation and dynamic mechanical analysis (DMA) are methods used to determine mechanical and viscoelastic material properties
In order to investigate optimal testing conditions for tungsten cone indenters, load, and overtones of the first order frequency, dynamic microindentations were performed on the narrow parallel area in the middle of the injection molded high density polyethylene (HDPE) tensile bars
In the earlier study [5], we found that for a tungsten cone indenter with a diameter of 0.5 mm, the overtones of the first order resonant frequency were considerably higher (55%) than 10% proposed by the manufacturer of the DMA 242C

Summary

Introduction

Micro- and nanoindentation and dynamic mechanical analysis (DMA) are methods used to determine mechanical and viscoelastic material properties. Materials respond to deformation differently on a local or bulk scale. Instrumented micro- and nanoindentation provide information about, for example, material stiffness, indentation hardness, and indentation modulus by evaluating loading and unloading curves during loading and unloading, respectively. Oliver and Pharr [1,2] made an enormous contribution to the development and the analysis of the indentation technique. Based on the theories of Hertz [3] and Sneddon [4], Oliver and Pharr developed the evaluation for several indenter geometries, for example, for the three-sided diamond Berkovich indenter, which is commonly used (see Theoretical Consideration)

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