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RESEARCH PAPERS

Size Effect on Compressive Strength of Sandwich Panels with Fracture of Woven Laminate Facesheet

[+] Author and Article Information
John Bayldon

Department of Civil and Environmental Engineering,  Northwestern University CAT#326, 2145 Sheridan Road, Evanston, IL 60208j-bayldon@northwestern.edu

Zdeněk P. Bažant

Department of Civil and Environmental Engineering,  Northwestern University A135, 2145 Sheridan Road, Evanston, IL 60208

Isaac M. Daniel

Department of Civil and Environmental Engineering,  Northwestern University CAT#326, 2145 Sheridan Road, Evanston, IL 60208

Qiang Yu

Department of Civil and Environmental Engineering,  Northwestern University, 2145 Sheridan Road, Evanston, IL 60208

J. Eng. Mater. Technol 128(2), 169-174 (Nov 02, 2005) (6 pages) doi:10.1115/1.2172277 History: Received March 23, 2005; Revised November 02, 2005

Prismatic sandwich specimens of various sizes, geometrically scaled in the ratio 1:2:4:8, are subjected to eccentric axial compression and tested to failure. The sandwich core consists of a closed-cell polyvinyl chloride foam, and the facesheets are woven glass-epoxy laminates, scaled by increasing the number of plies. The test results reveal a size effect on the mean nominal strength, which is strong enough to require consideration in design. The size effect observed is fitted with the size effect law of the energetic (deterministic) size effect theory. However, because of inevitable scatter and limited testing range, the precise form of the energetic size effect law to describe the test results is not unambiguous. The Weibull-type statistical size effect on the mean strength is ruled out because the specimens had small notches which caused the failure to occur in only one place in the specimen, and also because the observed failure mode was kink band propagation, previously shown to cause energetic size effect. Various fallacies in previous applications of Weibull theory to composites are also pointed out.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 2

Specimens showing size variation

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Figure 3

Development of fracturing compressive kink band at the notch in the laminate skin

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Figure 4

Measured values (data points) of nominal strength σN of eccentrically compressed sandwich prisms of various sizes (thicknesses) D, plotted as log(σN−σr) versus logD, and the their fit by type 2 size effect law, Eq. (3). Left: Porous laminate skins from standard manufacture. Right: Nonporous laminate skins.

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Figure 5

The same data and fits as in Fig. 4, but replotted as (σN−σr)−2 versus D, to obtain a linear regression plot.

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Figure 6

Top: The same data as on top of Fig. 4, but fitted with the type 1 size effect law, Eq. 2. Bottom: The same as on top but replotted as σN−1∕r versus 1/D, to obtain a linear regression plot.

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