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Research Papers

Quasi-Static Three-Point Bending of Carbon Fiber Sandwich Beams With Square Honeycomb Cores

[+] Author and Article Information
B. P. Russell1

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

T. Liu, N. A. Fleck, V. S. Deshpande

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

Intertronics, 17 Station Field Industrial Estate, Banbury Road, Kidlington, Oxfordshire OX5 1JD, UK.

Excel Composites, Duxford, UK.

Sika, Watchmead, Welwyn Garden City, Hertfordshire AL7 1BQ, UK.

1

Corresponding author.

J. Appl. Mech 78(3), 031008 (Feb 15, 2011) (15 pages) doi:10.1115/1.4003221 History: Received November 02, 2010; Revised December 07, 2010; Posted December 09, 2010; Published February 15, 2011; Online February 15, 2011

Sandwich beams comprising identical face sheets and a square honeycomb core were manufactured from carbon fiber composite sheets. Analytical expressions were derived for four competing collapse mechanisms of simply supported and clamped sandwich beams in three-point bending: core shear, face microbuckling, face wrinkling, and indentation. Selected geometries of sandwich beams were tested to illustrate these collapse modes, with good agreement between analytic predictions and measurements of the failure load. Finite element (FE) simulations of the three-point bending responses of these beams were also conducted by constructing a FE model by laying up unidirectional plies in appropriate orientations. The initiation and growth of damage in the laminates were included in the FE calculations. With this embellishment, the FE model was able to predict the measured load versus displacement response and the failure sequence in each of the composite beams.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 10

The measured (i) core compression εc, (ii) core shear strain γc, and (iii) face-sheet strain εf for three selected geometries A, C, and H. The simply supported beams are (a), (c), and (e), while the clamped geometries are (b), (d), and (f).

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Figure 11

Side views of the observed and predicted deformation/failure modes of three selected simply supported beam geometries just after the peak load was attained: (a) geometry A, (b) geometry C, and (c) geometry H. The FE predictions are shaded with contours of the damage variable ds, and the beam displacement δ for each case is indicated.

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Figure 12

Side views of the observed and predicted deformation/failure modes of three selected clamped beam geometries just after the peak load was attained: (a) geometry A, (b) geometry C, and (c) geometry H. The FE predictions are shaded with contours of the damage variable ds, and the beam displacement δ for each case is indicated.

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Figure 13

(a) Sketch illustrating the coordinate system for a single ply of a unidirectional laminate and (b) the assumed equivalent stress versus strain relationship for each of the four damage modes. Unloading from a damaged state occurs linearly toward the origin, as shown in (b).

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Figure 14

Images showing the FE predictions of damage ds just after the peak load has been attained in selected simply supported sandwich beams: (a) geometry A, (b) geometry C, and (c) geometry H. The roller is included to better illustrate the locations of the damage, and images with both the top face sheet present and absent are included so as to visualize the face sheet and core damage clearly.

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Figure 15

Images showing the FE predictions of damage ds just after the peak load has been attained in selected clamped sandwich beams: (a) geometry A, (b) geometry C, and (c) geometry H. The roller is included to better illustrate the locations of the damage, and images with both the top face sheet present and absent are included so as to visualize the face sheet and core damage clearly.

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Figure 16

Comparison of measured and finite element calculations for selected strains: (i) core compression εc, (ii) core shear strain γc, and (iii) face-sheet strain εf for three selected geometries A, C, and H. The simply supported beams are (a), (c), and (e), while the clamped geometries are (b), (d), and (f).

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Figure 1

Sketches of the slotting technique used to assemble (a) the square honeycomb sandwich cores and (b) the assembled sandwich beams. The coordinate system associated with the core and beam and the notation used to indicate the dimensions of the honeycomb core and sandwich beam are included.

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Figure 2

Sketches of (a) the clamping fixture for the sandwich beams and (b) the sandwich beams with end portions filled with epoxy so as to allow high clamping pressures to be applied

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Figure 3

The measured tensile and compressive quasi-static stress versus strain responses of the (a) laminate composite (comprising two orthogonal unidirectional plies) and (b) the woven composite materials. The responses are shown for both the 0–90 deg and ±45 deg orientations. The corresponding predictions of the calibrated constitutive model are also included.

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Figure 4

The measured compressive (σ33−ε33) and shear (τ13−γ13) responses of the ρ¯=0.1 composite square honeycomb core. From Russell (8).

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Figure 5

Sketches of the loading configuration of the sandwich beams in the (a) simply supported and (b) clamped configurations

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Figure 6

Sketches illustrating the four principal collapse modes of the clamped and simply supported composite sandwich beams

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Figure 7

Collapse mechanism maps for the (a) simply supported and (b) clamped sandwich beams with a square honeycomb core of relative density ρ¯=0.1. The beams have n=5 walls across the width b of the beams. The geometries tested in this study are marked on the map along with contours of the nondimensional collapse load F¯.

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Figure 9

The measured load versus displacement curves for three selected geometries A, C, and H. The simply supported beams are (a), (c), and (e), while the clamped geometries are (b), (d), and (f). The corresponding FE predictions along with the observed and predicted collapse modes are also included.

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Figure 8

Sketch illustrating the instrumentation employed to measure the core compression strain εc, core shear strain γc, face-sheet strain εf, and the roller displacement δ

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