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Research Papers

The Through-Thickness Compressive Strength of a Composite Sandwich Panel With a Hierarchical Square Honeycomb Sandwich Core

[+] Author and Article Information
F. Côté, B. P. Russell, V. S. Deshpande, N. A. Fleck

Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK

Trade name of Dupont referring to an aramid paper impregnated with epoxy resin.

J. Appl. Mech 76(6), 061004 (Jul 23, 2009) (8 pages) doi:10.1115/1.3086436 History: Received August 09, 2007; Revised January 11, 2009; Published July 23, 2009

Sandwich panels with aluminum alloy face sheets and a hierarchical composite square honeycomb core have been manufactured and tested in out-of-plane compression. The prismatic direction of the square honeycomb is aligned with the normal of the overall sandwich panel. The cell walls of the honeycomb comprise sandwich plates made from glass fiber/epoxy composite faces and a polymethacrylimide foam core. Analytical models are presented for the compressive strength based on three possible collapse mechanisms: elastic buckling of the sandwich walls of the honeycomb, elastic wrinkling, and plastic microbuckling of the faces of the honeycomb. Finite element calculations confirm the validity of the analytical expressions for the perfect structure, but in order for the finite element simulations to achieve close agreement with the measured strengths it is necessary to include geometric imperfections in the simulations. Comparison of the compressive strength of the hierarchical honeycombs with that of monolithic composite cores shows a substantial increase in performance by using the hierarchical topology.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Sketch of a square honeycomb core with the cell walls of the core made from a mesoscopic sandwich panels, (b) schematic of the unit cell and geometrical parameters employed in the analytical model and finite element analysis, and (c) torsional-axial buckling mode of square honeycomb core

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Figure 2

Collapse mechanism map and contours of normalized strength σ¯≡Pcr/Pmb of the hierarchical square honeycomb made from elastic face and polymeric foam core of relative density (a) ρ¯=0.06 and (b) ρ¯=0.20. The six tested geometries are marked on the map (a).

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Figure 3

Photographs a specimen with l=75 mm and t=0.6 mm demonstrating the manufacturing technique: (a) a waterjet machined panel, (b) the assembling technique, and (c) the final product

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Figure 4

(a) The measured compressive and shear responses of the eight harness satin weave 7781 E-glass/epoxy composite and (b) the measured uniaxial compressive response of the PMI foam (Rohacell 71 IG) used for the mesoscopic sandwich panel

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Figure 5

The measured compressive response of square honeycomb specimens with (a) l=60 mm and t=0.2 mm, (b) l=30 mm and t=0.2 mm, (c) l=75 mm and t=0.6 mm, (d) l=60 mm and t=0.6 mm, (e) l=45 mm and t=0.6 mm, and (f) l=30 mm and t=0.6 mm. Also added in the figure is the compressive strength predicted by analytical models, FE buckling analysis, and FE static analysis with an imperfection of ς≡w/l=0.3%.

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Figure 6

Finite element predictions of the first eigenmode extracted for the specimen with (a) l=30 mm and t=0.2 mm, (b) l=75 mm and t=0.6 mm, and (c) l=30 mm and t=0.6 mm

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Figure 7

FE predictions of the compressive response of specimens with (a) l=30 mm and t=0.2 mm, (b) l=75 mm and t=0.6 mm, and (c) l=30 mm and t=0.6 mm. Imperfections in the first eigenmode with maximum amplitude ς≡w/l are specified.

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Figure 8

Sketch of a conventional monolithic square honeycomb showing the geometrical parameters along with the manufacturing technique of the monolithic square honeycomb

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Figure 9

Comparison between the measured and predicted compressive strength of square honeycombs made from monolithic GFRP laminates and sandwich walls with face sheets of (a) t=0.6 mm and (b) t=0.2 mm

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