Research Papers

Effect of Distribution Media Length and Multiwalled Carbon Nanotubes on the Formation of Voids in VARTM Composites

[+] Author and Article Information
Levent Aktas, Duane P. Bauman, Scott T. Bowen, Mrinal C. Saha

 School of Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019

M. Cengiz Altan1

 School of Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019altan@ou.edu


Corresponding author.

J. Eng. Mater. Technol 133(4), 041006 (Oct 14, 2011) (9 pages) doi:10.1115/1.4004700 History: Received April 04, 2011; Revised July 19, 2011; Accepted July 22, 2011; Published October 14, 2011; Online October 14, 2011

The first part of this paper characterizes the effect of tooling and process parameters such as the length of distribution media used in vacuum assisted resin transfer molding (VARTM) of composite laminates. To achieve this goal, a number of 6-ply, woven carbon fiber/epoxy laminates are fabricated by using various lengths of distribution media. The spatial variations of mechanical properties of these laminates are characterized using a three-point bending fixture. It is shown that for relatively thinner laminates, extending the distribution media degrades the flexural properties by as much as 14%, possibly due to air pockets entrapped during through-the-thickness impregnation of the fibrous fabric. In the second part, a minimum distribution media length is used to investigate the mechanical property and microstructure changes due to multiwalled carbon nanotubes (MWNTs) dispersed in the composite laminates. In addition, effects of different nanotube functionalization and morphology are characterized via scanning electron microscopy and optical microscopy. To achieve adequate nanotube dispersion in the epoxy resin, both tip sonication and mechanical mixing have been used. The effect of sonication time on the dispersion of nanotubes is reported by monitoring the temporal changes in the nanotube cluster size. Even at volume fractions less than 1%, almost 10% improvements in flexural properties is observed. Extensive void formations are reported for laminates containing MWNTs, possibly preventing greater improvements in mechanical properties.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic representation of the VARTM process. (a) Top view and (b) side view. Note that the vacuum bag is not shown in the top view.

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Figure 2

Spatial arrangement of samples prepared from each laminate for three-point bending tests (samples 1–15) and void content characterization via optical microscopy (samples Void 1–Void 4). Dimensions are in millimeters.

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Figure 3

Effect of distribution media length on the flexural properties of composite laminates fabricated by VARTM

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Figure 4

Flexural properties and average void content, φ, of carbon/epoxy laminates containing different amounts of MWNTs

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Figure 5

Scanning electron micrograph of as-received –COOH functionalized, short MWNTs before mixing

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Figure 6

Scanning electron micrographs of three types of laminates studied. N: Nonfunctionalized, S: –COOH functionalized, short MWNT and L: –COOH functionalized, long MWNT.

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Figure 7

Optical micrographs of epoxy resin mixed with MWNT before (left) and after (right) sonication. N: Nonfunctionalized, S: –COOH functionalized, short MWNT and L: –COOH functionalized, long MWNT.

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Figure 8

Evolution of the MWNT average cluster area as the sonication progresses

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Figure 9

Flexural properties and void contents of carbon/epoxy laminates containing different types of MWNTs

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Figure 10

Typical, periodic void formation patterns observed in the nanocomposites fabricated with nonfunctionalized MWNTs. Scanning electron micrograph captured at 10X magnification.

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Figure 11

Void content distribution in the flow direction and its effects on the flexural properties of carbon/epoxy laminates containing different types of MWNTs. Bars graphs indicate void content. Line graphs indicate flexural strength.

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Figure 12

Flexural strength and stiffness of five samples with the highest values




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