A Comparison of the Structural Response of Clamped and Simply Supported Sandwich Beams With Aluminium Faces and a Metal Foam Core

[+] Author and Article Information
V. L. Tagarielli

 Engineering Department, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdom

N. A. Fleck

 Engineering Department, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdomnaf1@eng.cam.ac.uk

European supplier, Karl Bula, Innovation Services, Ch-5200 Brugg, Herrenmatt 7F, Switzerland.

J. Appl. Mech 72(3), 408-417 (Sep 18, 2004) (10 pages) doi:10.1115/1.1875432 History: Received March 05, 2004; Revised September 18, 2004

Plastic collapse modes for clamped sandwich beams have been investigated experimentally and theoretically for the case of aluminium face sheets and a metal foam core. Three initial collapse mechanisms have been identified and explored with the aid of a collapse mechanism map. It is shown that the effect of clamped boundary conditions is to drive the deformation mechanism towards plastic stretching of the face sheets. Consequently, the ultimate strength and level of energy absorption of the sandwich beam are set by the face sheet ductility. Limit load analyses have been performed and simple analytical models have been developed in order to predict the postyield response of the sandwich beams; these predictions are validated by both experiments and finite elements simulations. It is shown experimentally that the ductility of aluminium face sheets is enhanced when the faces are bonded to a metal foam core. Finally, minimum weight configurations for clamped aluminium sandwich beams are obtained using the analytical formulas for sandwich strength, and the optimal designs are compared with those for sandwich beams with composite faces and a polymer foam core.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Geometries of simply supported and clamped sandwich beams transversely loaded by a flat punch

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Figure 2

Initial collapse by face yielding of sandwich beams (a) simply supported case and (b) built-in case

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Figure 3

Two alternative modes of initial collapse by core shear

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Figure 4

Initial collapse of sandwich beams by indentation of the upper face sheet

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Figure 5

Initial collapse mechanism map for simply supported and clamped sandwich beams in three-point bending. σ¯=0.034 and a¯=0.1. Test geometries are marked on the map.

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Figure 6

Stages of collapse of simply supported and clamped sandwich beams

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Figure 7

Tensile response of the annealed aluminium face sheets

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Figure 8

The loading configurations, with boundary conditions used in the finite element calculations

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Figure 9

Measured load vs deflection response and photographs of simply supported and clamped sandwich beams. Initial collapse is by (a) face yield, (b) core shear, and (c) indentation

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Figure 10

Comparison of measured and predicted collapse responses for sandwich beams collapsing by (a) face yield, (b) core shear, and (c) indentation

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Figure 11

Comparison of measure and analytical prediction of initial collapse strength for the specimens listed in Table 2

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Figure 12

Collapse mechanism map with contours of the nondimensional strength and mass index (σ¯=0.034,a¯=0.1,ρ¯=0.11). The minimum mass trajectory is included.

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Figure 13

Normalized minimum mass vs structural load index for a clamped sandwich beam of metallic construction and of composite construction (key: FM = face microbuckling, FY = face yield, CS = core shear, IN = indentation)

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Figure 14

Scanning electron micrographs of the tensile necks in (a) aluminium alloy face sheet with no foam support, and (b) aluminium alloy face sheet as part of a sandwich plate. (c) Measured tensile load vs strain response for a sandwich dog-bone specimen. The predicted response by an upper bound, rule-of-mixtures calculation is included.

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Figure 15

Sensitivity of tensile ductility of dog-bone sandwich specimens to the ratio of face sheet to core thickness



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