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Research Papers

On the Use of Pressure-Loaded Blister Tests to Characterize the Strength and Durability of Proton Exchange Membranes

[+] Author and Article Information
David A. Dillard1

Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219dillard@vt.edu

Yongqiang Li2

Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219

Jacob R. Grohs, Scott W. Case

Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219

Michael W. Ellis

Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0238

Yeh-Hung Lai, Michael K. Budinski, Craig S. Gittleman

Fuel Cell Research Lab, Global R&D, General Motors Corporation, Honeoye Falls, NY 14472-0603

Nafion® is a registered trademark of E. I. du Pont de Nemours and Company of Wilmington, DE.

Swagelok® is a registered trademark of Swagelok Company, Solon, OH.

Gore™ Select® is a trademark of W. L. Gore & Associates, Inc. of Newark, DE.

Ion Power™ is a trademark of Ion Power, Inc. of New Castle, DE.

Devcon® is a registered trademark of ITW Devcon, Danvers, MA.

KDScientific® is a registered trademark of KDScientific Inc., Holliston, MA.

Becton Dickinson® is a registered trademark of Becton, Dickinson and Company, Franklin Lakes, NJ.

Sensotec® is a registered trademark of Honeywell International Inc., Columbus, OH.

LABVIEW® is a registered trademark of National Instruments, Inc., Austin, TX.

Fisher Scientific™ is a trademark of Fisher Scientific Inc., Pittsburg, PA.

TA Instruments™ is a trademark of TA Instruments Inc., New Castle, DE.

1

Corresponding author.

2

Present address: Fuel Cell Research Lab, Global R&D, General Motors Corporation, Honeoye Falls, NY 14472-0603.

J. Fuel Cell Sci. Technol 6(3), 031014 (May 15, 2009) (8 pages) doi:10.1115/1.3007431 History: Received June 26, 2007; Revised December 14, 2007; Published May 15, 2009

The use of pressurized blister specimens to characterize the biaxial strength and durability of proton exchange membranes (PEMs) is proposed, simulating the biaxial stress states that are induced within constrained membranes of operating PEM fuel cells. PEM fuel cell stacks consist of layered structures containing the catalyzed PEMs that are surrounded by gas diffusion media and clamped between bipolar plates. The surfaces of the bipolar plates are typically grooved with flow channels to facilitate distribution of the reactant gases and water by-product. The channels are often on the order of a few millimeters across, leaving the sandwiched layers tightly constrained by the remaining lands of the bipolar plates, preventing in-plane strains. The hydrophilic PEMs expand and contract significantly as the internal humidity, and to a lesser extent, temperature varies during fuel cell operation. These dimensional changes induce a significant biaxial stress state within the confined membranes that are believed to contribute to pinhole formation and membrane failure. Pressurized blister tests offer a number of advantages for evaluating the biaxial strength to bursting or to detectable leaking. Results are presented for samples of three commercial membranes that were tested at 80°C and subjected to a pressure that was ramped to burst. The bursting pressures exhibit significant time dependence that is consistent with failure of viscoelastic materials. Rupture stresses, estimated with the classic Hencky’s solution for pressurized membranes in conjunction with a quasielastic estimation, are shown to be quite consistent for a range of blister diameters tested. The technique shows considerable promise not only for measuring biaxial burst strength but also for measuring constitutive properties, creep to rupture, and cyclic fatigue damage. Because the tests are easily amenable to leak detection, pressurized blister tests offer the potential for characterizing localized damage events that would not be detectable in more commonly used uniaxial strength tests. As such, this specimen configuration is expected to become a useful tool in characterizing mechanical integrity of proton exchange membranes.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Plot of radial and tangential stress factors as a function of radial position for a pressurized circular blister

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Figure 2

Plot of the stress state uniformity within a pressurized circular blister, showing the ratio of tangential to radial stresses and the ratio of radial stress to the maximum central stress

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Figure 3

Illustrations of (a) a standard Swagelok® tube fitting (adapted from animations available at http://www.swagelok.com); (b) a cross-sectional diagram describing the sample preparation process (not to scale); (c) the clamping and pressurizing of a sample with the modified fitting (not to scale), and note the machined ferrule nut; (d) the connections involved in a blister test. After the specimen was clamped onto the tube fitting, it was inserted into the oven from the top.

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Figure 4

High speed photographs of a Gore™ Select® series 57 membrane rupturing at room temperature measured at 5500fps

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Figure 5

Illustrations of (a) a typical pressure trace of Gore™ Select® series 57 tested at 80°C at an infusion rate of 14ml∕min and (b) a typical pressure traces valid and invalid test results for specimens tested at 80°C with an infusion rate of 14ml∕min

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Figure 6

Illustration of typical pressure trace converted to stress history using Hencky’s solution (Gore™ Select® series 57 at 80°C with an infusion rate of 14ml∕min)

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Figure 7

(a) Burst pressures of blisters tested at different rates and with different sizes of ferrules; (b) time-dependent burst strength of Gore™ Select® series 57 at 80°C calculated from peak pressure shown in (a)

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Figure 8

Burst strengths of Nafion® NRE-211, Gore™ Select® series 57, and Ion Power™ Nafion® N111-IP

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