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Research Papers

Characterization and Modeling of Large Displacement Micro-/Nano-Indentation of Polymeric Solids

[+] Author and Article Information
Y. C. Lu1

Department of Mechanical Engineering, University of Kentucky, Paducah, KY 42002chlu@engr.uky.edu

D. M. Shinozaki

Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, N6A 5B9, Canada

1

Corresponding author.

J. Eng. Mater. Technol 130(4), 041001 (Aug 26, 2008) (7 pages) doi:10.1115/1.2969250 History: Received July 13, 2007; Revised December 18, 2007; Published August 26, 2008

Large displacement micro-indentation tests have been performed on various polymeric solids to measure the plastic properties. Cylindrical flat-ended indenters with diameter in the range of 1090μm are mostly used. The mechanism of large-strain indentation has been examined with optical microscopy and finite element simulations. Results show that under a flat-tipped indenter, the material can quickly reach a fully plastic state. The size (diameter) of the plastic zone is constant in large-strain regions and unaffected by the exact tip profile (flat, spherical, and conical). The indentation stress-displacement curve at large strains is linear as a result of the steady-state plastic flow, from which the mean indentation pressure, a measure of yield strength, can be readily extrapolated. The indentation stress-displacement response is independent of the indenter diameters but strongly dependent on the strain-hardening behavior of the material and the friction between a material and an indenter. Compared with other shaped indenters, the flat-ended indenter requires the least penetration depth in order to probe the plastic properties of a material or structure.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic showing the large displacement indentation test: (a) side view and (b) top view

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Figure 2

Transmitted light micrographs of HDPE under cross polarizers showing the development of the plastic zone surrounding the indenter (cross-sectional)

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Figure 3

Transmitted light micrograph of (a) PS and (b) PMMA under cross polar showing the development of the plastic zone surrounding the indenter (top views)

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Figure 4

Indentation stress-displacement curves of HDPE with different indenter diameters

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Figure 5

Indentation stress-displacement curves of polymeric solids

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Figure 6

Contours of equivalent plastic strain of HDPE showing the development of the plastic zone surrounding the indenter (cross-sectional view): (a) residual state and (b) fully loaded state

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Figure 7

Residual equivalent plastic strain of HDPE showing the development of the plastic zone surrounding the indenter (top view)

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Figure 8

Effect of interfacial fiction between indenter sidewall and surrounding material on indentation stress-displacement responses of HIPS

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Figure 9

Effect of indenter size on indentation stress-displacement response of HIPS

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Figure 10

Effect of elastic modulus on indentation stress-displacement responses of HIPS

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Figure 11

Effect of strain-hardening on indentation stress-displacement response of HIPS

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Figure 12

Contours of equivalent plastic strain under cylindrical indenters of various tip geometries in fully loaded state of HIPS: (a) flat tip with straight edge, (b) flat tip with rounded tip, (c) spherical tip, and (d) conical tip

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Figure 13

Effect of indenter tip profile on indentation load-displacement responses of HIPS

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