Research Papers

Mechanical Behavior of Epoxy-Graphene Platelets Nanocomposites

[+] Author and Article Information
A. Zandiatashbar, N. Koratkar

 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180

R. C. Picu1

 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180e-mail: picuc@rpi.edu


Corresponding author.

J. Eng. Mater. Technol 134(3), 031011 (May 07, 2012) (6 pages) doi:10.1115/1.4006499 History: Received October 16, 2011; Revised January 07, 2012; Online May 07, 2012; Published May 16, 2012

Various aspects of the mechanical behavior of epoxy-based nanocomposites with graphene platelets (GPL) as additives are discussed in this article. The monotonic loading response indicates that at elevated temperatures, the elastic modulus and the yield stress are significantly improved in the composite as compared to neat epoxy. The activation energy for creep is smaller in neat epoxy, which indicates that the composite creeps less, especially at elevated temperatures and higher stresses. The composites also exhibit larger fracture toughness. When subjected to cyclic loading, fatigue crack growth rate is smaller in the composite relative to neat epoxy. This reduction is important by at least an order of magnitude at all stress intensity factor amplitudes. Optimal property improvements in the monotonic, cyclic, and fracture behaviors are obtained for very low filling fraction of approximately 0.1 wt. %. Similar differences in the mechanical behavior are observed when the composite is probed on the local scale by nanoindentation.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

(a) SEM micrograph of a fracture surface of the 0.1 wt. % epoxy-GPL nanocomposite after failure. The inset shows a region of the main image at higher magnification. The inclusions can be easily distinguished from the river pattern features, as indicated in the inset. (b) Probability distribution function of inclusion size in 0.1 and 0.5 wt. % epoxy-GPL nanocomposites obtained by image processing of fracture surface micrographs [14].

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Figure 2

(a) Engineering stress versus engineering strain plots for neat epoxy, 0.1 and 0.2 wt. % epoxy-GPL nanocomposites. Symbols are added to the curve just for labeling. (b) Relative magnitude of the 0.2% yield stresses of the composite and neat epoxy (computed as (σycomp-σyepoxy)/(σyepoxy)), versus temperature. Data for composites with 0.1 and 0.2 wt. % GPL are shown. The nonmonotonic variation of the GPL0.1 curve is expected to be due to the variability from sample to sample. However, the increasing trend of the measure shown is clear and independent of the measurement noise.

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Figure 3

Log–log plot of creep strain versus time (in seconds) for neat epoxy and 0.1 wt. % epoxy-GPL showing a power law creep compliance function [14]

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Figure 4

Creep strain versus time for neat epoxy and 0.1 wt. % epoxy-GPL at a stress of 20 MPa and temperatures of 23, and 55 °C [14]

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Figure 5

Fracture toughness values for neat epoxy, 0.1, and 0.2 wt. % epoxy-GPL nanocomposites at room temperature, 55, and 70 °C

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Figure 6

Fatigue crack growth rate (da/dN) versus stress intensity factor amplitude (ΔK) for neat epoxy and 0.1 wt. % filled epoxy with SWNT, MWNT, and GPL [10]

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Figure 7

(a) Top-view optical image of the surface of a 0.1 wt. % epoxy-GPL nanocomposite film. Sites where nanoindentation is performed are indicated. (b) AFM 3D image of GPL protrusions on the film surface after being etched with acetone.

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Figure 8

(a) Load-displacement curves for single-cycle and multiple-cycle nanoindentation in the neat epoxy film (solid line) and the nanocomposite film (dashed line). The plot shows a good repeatability from indentation to indentation. (b) Multiple-cycle indentation in the nanocomposite film, at and away from GPL protrusions (Fig. 7) [20].



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