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Research Papers

Sandwich Beams With Corrugated and Y-frame Cores: Does the Back Face Contribute to the Bending Response?

[+] Author and Article Information
L. St-Pierre, V. S. Deshpande

Department of Engineering,  University of Cambridge, Trumpington Street, Cambridge, CP2 1PZ, UK

N. A. Fleck1

Department of Engineering,  University of Cambridge, Trumpington Street, Cambridge, CP2 1PZ, UKnaf1@eng.cam.ac.uk

Damen Schelde Naval Shipbuilding, Glacisstraat 165, 4381 SE Vlissingen, Netherlands.

Astech Engineering Products Inc., 3030 Red Hill Ave., Santa Ana, CA 92705.

1

Corresponding author. Tel: +44 1223 748240 Fax: +44 1223 332662 Email: naf1@eng.cam.ac.uk

J. Appl. Mech 79(1), 011002 (Nov 14, 2011) (13 pages) doi:10.1115/1.4004555 History: Received February 01, 2011; Revised June 25, 2011; Posted July 11, 2011; Published November 14, 2011; Online November 14, 2011

Stainless steel sandwich beams with a corrugated core or a Y-frame core have been tested in three-point bending and the role of the face-sheets has been assessed by considering beams with (i) front-and-back faces present, and (ii) front face present but back face absent. A fair comparison between competing beam designs is made on an equal mass basis by doubling the front face thickness when the back face is absent. The quasi-static, three-point bending responses were measured under simply supported and clamped boundary conditions. For both end conditions and for both types of core, the sandwich beams containing front-and-back faces underwent indentation beneath the mid-span roller whereas Brazier plastic buckling was responsible for the collapse of sandwich beams absent the back face. Three-dimensional finite element (FE) predictions were in good agreement with the measured responses and gave additional insight into the deformation modes. The FE method was also used to study the effect of (i) mass distribution between core and face-sheets and (ii) beam span upon the collapse response of a simply supported sandwich panel. Sandwich panels of short span are plastically indented by the mid-span roller and the panels absent a back face are stronger than those with front-and-back faces present. In contrast, sandwich panels of long span undergo Brazier plastic buckling, and the presence of a back face strengthens the panel.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The Y-frame sandwich core in (a) double hull and (b) single hull designs

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Figure 2

The design space for mass distribution within a sandwich panel of areal mass m. The proportion of mass in the core, in the front face and in the back face are denoted by mc /m, mf /m and mb /m, respectively. The mass distribution of the test geometries is indicated for two choices of areal mass.

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Figure 3

Measured uniaxial tensile responses of as-brazed AISI 304 stainless steel and Lloyd’s Grade A steel, at a strain rate of 10−3 s−1

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Figure 4

Cross-sectional dimensions of the sandwich beams: (a) corrugated core and (b) Y-frame core. (c) The chosen values of face-sheet thickness used in the experimental study. All dimensions are in mm.

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Figure 5

The test fixtures used for (a) simply supported and (b) clamped beams. A sandwich beam with a Y-frame core and absent the back face is shown. All dimensions are in mm.

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Figure 6

Three-point bending responses of simply supported sandwich beams. Sandwich beams with an areal mass m = 9.1 kg/m2 are shown with (a) a corrugated core and (b) a Y-frame core. Likewise, sandwich beams with an areal mass m = 13.8 kg/m2 are shown with (c) a corrugated core and (d) a Y-frame core.

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Figure 7

Three-point bending responses of clamped sandwich beams. Sandwich beams with an areal mass m = 9.1 kg/m2 are shown with (a) a corrugated core and (b) a Y-frame core. Likewise, sandwich beams with an areal mass m = 13.8 kg/m2 are shown with (c) a corrugated core and (d) a Y-frame core.

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Figure 8

Photographs of the simply supported sandwich beams with a corrugated core (m = 13.8 kg/m2 ) (a) with front-and-back faces and (b) without a back face. Deformed finite element meshes of the same sandwich beam (c) with front-and-back faces and (d) without a back face. A side view showing half of the beam and a view of the core deformation at mid-span are given. To clarify the predicted deformation modes, the undeformed (dashed line) and deformed (solid line) cross sections at mid-span are included in Figs. 8(c) and 8(d). The images are for beams loaded to δ = 0.2L and then unloaded.

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Figure 9

Photographs of the simply supported sandwich beams with a Y-frame core (m = 13.8 kg/m2 ) (a) with front-and-back faces and (b) without a back face. Deformed finite element meshes of the same sandwich beam (c) with front-and-back faces and (d) without a back face. A side view showing half of the beam and a view of the core deformation at mid-span are given. To clarify the predicted deformation modes, the undeformed (dashed line) and deformed (solid line) cross sections at mid-span are included in Figs. 9(c) and 9(d). The images are for beams loaded to δ = 0.2L and then unloaded.

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Figure 10

Photographs of the clamped sandwich beams with a corrugated core (m = 13.8 kg/m2 ) (a) with front-and-back faces and (b) without a back face. Deformed finite element meshes of the same sandwich beam (c) with front-and-back faces and (d) without a back face. A side view showing half of the beam and a view of the core deformation at mid-span are given. To clarify the predicted deformation modes, the undeformed (dashed line) and deformed (solid line) cross sections at mid-span are included in Figs. 10(c) and 10(d). The images are for beams loaded to δ = 0.2L and then unloaded.

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Figure 11

Photographs of the clamped sandwich beams with a Y-frame core (m = 13.8 kg/m2 ) (a) with front-and-back faces and (b) without a back face. Deformed finite element meshes of the same sandwich beam (c) with front-and-back faces and (d) without a back face. A side view showing half of the beam and a view of the core deformation at mid-span are given. To clarify the predicted deformation modes, the undeformed (dashed line) and deformed (solid line) cross sections at mid-span are included in Figs. 11(c) and 11(d). The images are for beams loaded to δ = 0.2L and then unloaded.

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Figure 12

Cross-sectional dimensions of the sandwich panels considered in the numerical analysis: (a) corrugated core and (b) Y-frame core. (c) The sandwich panels, shown here with a corrugated core, are simply supported and loaded in three-point bending.

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Figure 13

Normalized peak load F∧=Fpk/(σYbc) as a function of the normalized span 2L/c for simply supported sandwich panels and selected values of mc /m (m/ρc = 0.052). Results are shown for sandwich panels with (a) a corrugated core and (b) a Y-frame core.

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Figure 14

The boundary conditions on FE models to simulate (a) indentation and (b) bending. A sandwich panel absent the back face is shown.

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Figure 15

(a) The predicted indentation response of sandwich panels with mc /m = 0.5 resting on a rigid foundation. (b) Normalized indentation strength F∧I=FI/(σYbc) as a function of mc /m (m/ρc = 0.052).

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Figure 16

(a) The predicted bending response of sandwich panels with mc /m = 0.5. (b) Normalized Brazier buckling moment M⌢=MB/(σYbc2) as a function of mc /m (m/ρc = 0.052).

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Figure 17

Normalized peak load F∧=Fpk/(σYbc) as a function of the normalized span 2L/c for simply supported sandwich panels and selected values of mc /m (m/ρc = 0.052). The three-point bending results are reproduced from Fig. 1. The indentation and Brazier buckling strengths are included as short and long dashed lines, respectively. Sandwich panels with front-and-back faces are shown with (a) a corrugated core and (b) a Y-frame core. Likewise, sandwich panels absent the back face are shown with (c) a corrugated core and (d) a Y-frame core.

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Figure 18

Normalized indentation strength per unit mass ρcF∧I/m as a function of mc /m for selected values of m/ρc. Results are shown for sandwich panels with (a) a corrugated core and (b) a Y-frame core.

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Figure 20

Sensitivity of the three-point bending response of a sandwich beam with a Y-frame core to the choice of material. (a) Front-and-back faces are present and (b) the back face is absent.

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Figure 19

Normalized Brazier buckling moment per unit mass ρcM∧/m as a function of mc /m for selected values of m/ρc. Results are shown for sandwich panels (a) with front-and-back faces present and (b) without a back face.

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