Metal Foams: A Design Guide

148 Metal Foams: A Design Guide
10.9 Recommendations for sandwich design
For those wishing to explore cellular metal core sandwich construction, the
following recommendations are pertinent:
1. Determine the constraints that govern the structure and, in particular,
whether it is stiffness or strength-limited.
2. If stiffness-limited, the procedure for determining the minimum weights is
straightforward, using the formulae summarized in the tables. It is important
to realize that there will always be lighter configurations (especially optimized
honeycomb or waffle panels). Those configurations should be explicitly
identified, whereupon a manufacturing cost and durability comparison
can be made that determines the viability of sandwich construction. Other
qualities of the cellular metal may bias the choice. It is important to calculate
the domains wherein the weights based on elasticity considerations
cannot be realized, because of the incidence of ‘inelastic’ modes: face
yielding, core yielding, face wrinkling. Some help in assessing these limits
has been provided.
3. When strength-limited (particularly when buckling-limited), the rules
governing sandwich construction are less well formulated. In general,
numerical methods are needed to compare and contrast this type of
construction with stiffened systems. Some general guidelines are given in
this Design Guide; these give insight into the loadings and configurations
most likely to benefit from sandwich construction. Configurations unlikely
to benefit are also described. It is recommended that where benefits seem
likely, detailed simulations and testing should be used to assess the viability
of sandwich construction.
References
Allen H.G. (1969) Analysis and Design of Structural Sandwich Panels, Pergamon Press, Oxford.
Andrews, E.H., Gioux, G., Onck, P. and Gibson, L.J. (1999) The role of specimen size, specimen
shape and surface preparation in mechanical testing of aluminum foams. To appear in Mat.
Sci. and Engineering A.
Bart-Smith, H. (2000) PhD thesis, Harvard University.
Budiansky, B. (1999) On the minimum weights of compression structures. Int. J. Solids and
Structures 36, 3677–3708.
Deshpande, V.S. and Fleck, N.A. (1999) Isotropic constitutive models for metallic foams. To
appear in J. Mech. Phys. Solids.
Gerard, G. (1956) Minimum Weight Analysis of Compression Structures, New York University
Press, New York.
Gibson, L.J. and Ashby, M.F. (1997) Cellular Solids, Structure and Properties, 2nd edition,
Cambridge University Press, Cambridge, Ch. 9, pp. 345 et seq.
Harte, A.-M. (1999) Private communication.
Hutchinson, J.W. and He, M.Y. (1999) Buckling of cylindrical sandwich shells with metal foam
cores. Int. J. Solids and Structures (in press).