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National Advisory Committee for Aeronautics, Technical Notes - Bending and Buckling of Rectangular Sandwich Plates

Differential equations and. boundary conditions are derived for the .
bending and buckling of sandwich plates. The buckling load is calculated
for a simply supported plate subjected to edgewise compression. -The
formulas obtained are evaluated numerically and. the results are plotted
in a diagram. The theory is in satisfactory agreement with results of
tests carried out at the Forest Products Laboratory.

The expression "sandwich plate" designates a composite plate con-
sisting of two thin faces and a thick core. In airplane construction
the faces are usually of aluminum alloy and the core is of some light-
weight material such as an expanded plastic or balsa wood. In the latter
'case the fibers of the wood are in general arranged perpendicularly to
the plane of the plate. Since thus the modulus of elasticity of the core
in the plane of the plate is of the order of magnitude of one-thousandth
of that of the faces, the normal stresses in the core are of little
importance in resisting bending moments even though the usual ratio of
face thickness to core thickness is between one—tenth and one-hundredth.
0n the other hand the core performs a task in transmitting shear forces
and undergoes considerable shearing deformations because its modulus of
shear is low. Hence shearing deformations must not be disregarded in
the analysis of sandwich plates.

In an earlier paper (reference 1) the differential equations of
bending were derived by means of the principle of virtual displacements
for sandwich beams subjected-to transverse and axial loads. Integration
of the equations yielded formulas for buckling load and deflection which
were found to be in good agreement with test results. For this reason
in the present paper the bending and the buckling of sandwich plates are
analyzed on the basis of the same assumptions as those underlying the
earlier investigation.