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National Advisory Committee for Aeronautics, Report - Elastic and Plastic Buckling of Simply Supported Solid Core Sandwich Plates in Compression

A solution is presented for the problem of the compressive
buckling of simplyr supported, fiat, rectangular, solid-core sand-
wich plates stressed either in the elastic range or in the plastic
range. Charts for the analysis of long sandwich plates are
presented for plates having face materials of 2481—11? aluminum
alloy, 75S—T6 Alclad aluminum alloy, and stainless steel.

A com pa-rison of computed and experimental buckling stresses
of square solid-core sandwich plates indicates fair agreement
between theory and experiment.

The necessary condition that the wing surfaces of modern
high—speed aircraft remain smooth under high loads has led
to the use of the sandwich plate as a substitute for sheet«
stringer construction. Sandwich plates consist of two thin
sheets of metal separated by a low—density, low-stiffness core
which, though contributing little to the strength of the plate,
serves to increase tremendously the flexural stiffness of the
load-carrying faces. The increase in flexural stiffness is
somewhat ofi’set, however, by deflections due to shear which
become appreciable because of the low stiffness of the core.

Several papers, which extend ordinary plate theory to
take into account deflections due to‘ shear, have appeared
recently in this country. The extension is made approxi-
mately in reference 1 by means of the assumption that any
line in the core that is initially straight and normal to the
middle surface of the core will remain straight after deforma-
tion but will deviate from the normal to the deformed middle
surface by an amount that is proportional to the slope of
the plate surface, the proportionality factor being the same
throughout the plate. The theory is used to obtain approxi-
mate criterions for the compressive buckling of plates with
various edge-support conditions. The criterions are cor-
rected for the effects of plasticity by replacing the Young’s
modulus of the face material everywhere it appears in the
buckling formulas by a reduced modulus, this method of
correction being partly justified by the consideration of its
theoretical efi’ectiveness in connection with the plastic
buckling of simply supported sandwich columns