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Research Papers

Delamination at Thick Ply Drops in Carbon and Glass Fiber Laminates Under Fatigue Loading

[+] Author and Article Information
Daniel D. Samborsky, Timothy J. Wilson, Pancasatya Agastra, John F. Mandell

Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717

J. Sol. Energy Eng 130(3), 031001 (Jun 13, 2008) (8 pages) doi:10.1115/1.2931496 History: Received March 06, 2006; Revised February 03, 2007; Published June 13, 2008

Delamination at ply drops in composites with thickness tapering has been a concern in applications of carbon fibers. This study explored the resistance to delamination under fatigue loading of carbon and glass fiber prepreg laminates with the same resin system, containing various ply drop geometries, and using thicker plies typical of wind turbine blades. Applied stress and strain levels to produce significant delamination at ply drops have been determined, and the experimental results correlated through finite element and analytical models. Carbon fiber laminates with ply drops, while performing adequately under static loads, delaminated in fatigue at low maximum strain levels except for the thinnest ply drops. The lower elastic modulus of the glass fiber laminates resulted in much higher strains to produce delamination for equivalent ply drop geometries. The results indicate that ply drops for carbon fibers should be much thinner than those commonly used for glass fibers in wind turbine blades.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic and photograph of typical ply drop coupon (two plies dropped at surface of 0deg stack)

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Figure 2

Maximum absolute strain to failure fatigue data for [±45∕08∕±45] control laminate, R=0.1, 10, and −1 (no ply drops; 0deg plies are carbon and ±45deg plies are glass)

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Figure 3

Maximum absolute stress to failure fatigue data for [±45∕08∕±45] control laminate, R=0.1, 10, and −1 (no ply drops; 0deg plies are carbon and ±45deg plies are glass)

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Figure 4

Maximum absolute strain versus cycles to failure and/or delamination for thin laminates with double ply drops [±45∕02*∕09∕02*∕±45], R=0.1, 10, and −1 (0deg plies are carbon and ±45deg plies are glass)

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Figure 5

Maximum absolute stress versus cycles to failure and/or delamination for thin laminates with double ply drops [±45∕02*∕09∕02*∕±45], R=0.1, 10, and −1 (0deg plies are carbon and ±45deg plies are glass)

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Figure 6

Photograph of delamination crack growing from pore ahead of double ply drop (see Fig. 1), carbon 0deg plies, compression fatigue (crack path enhanced)

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Figure 7

Strain-cycle results for a [(±45)3∕0n*∕027∕0n*(±45)3] laminate with n=1,2,4; plies dropped at the surface of the 0deg stack, R=10 (0deg plies are carbon and ±45deg plies are glass)

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Figure 8

Stress-cycles results for a [(±45)3∕0n*∕027∕0n*∕(±45)3] laminate with n=1,2, and 4; plies dropped at the surface of the 0deg stack, R=10 (0deg plies are carbon and ±45deg plies are glass)

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Figure 9

Comparison of strain-cycles data for a thick [(±45)3∕02*∕027∕02*∕(±45)3] laminate and a thin [±45∕02*∕09∕02*∕±45] laminate; double surface ply drops (0deg plies are carbon and ±45° plies are glass)

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Figure 10

Comparison of strain-cycles data for surface [(±45)3∕02*∕027∕02*∕(±45)3] and internal [(±45)3∕09∕02*∕09∕02*∕09∕(±45)3] double ply drops, R=10 (0deg plies are carbon and ±45deg plies are glass)

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Figure 11

Strain-cycles results for an all-fiberglass laminate [(±45)3∕0n*∕027∕0n*∕(±45)3] with n=1,2, and 4; plies dropped at the surface of the 0deg stack, R=10 (0deg and ±45deg plies are glass)

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Figure 12

Stress-cycle results for an all-fiberglass laminate [(±45)3∕0n*∕027∕0n*(±45)3] with n=1, 2, and 4 plies dropped at the surface of the 0deg stack, R=10 (0deg and ±45deg plies are glass)

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Figure 13

Strain-cycles comparison for laminates with carbon versus glass 0deg plies; double interior ply drops [(±45)3∕09∕02*∕09∕02*∕09∕(±45)3] (±45deg plies are glass)

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Figure 14

Strain-cycle comparison for laminates with carbon versus glass 0deg plies; double exterior ply drops [(±45)3∕02*∕027∕02*∕(±45)3] (±45deg plies are glass).

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Figure 15

Finite element model showing internal ply drop, delamination cracks, and pore ahead of ply drop.

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Figure 16

Comparison of glass and carbon FEA results for internal ply drop under tensile load, total GII component for both cracks (GI≈0), thin side strain=0.5%

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Figure 17

Same FEA case as Fig. 1, but compression load (same strain), carbon 0deg plies

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