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National Advisory Committee for Aeronautics, Technical Notes - Plastic Buckling of Simply Supported Compressed Plates

An investigation was made to ascertain the validity of various
theories for the plastic buckling of compressed simply supported plates
by means of local- ~instability tests of drawn square tubes of th-T6
aluminum alloy.

The results obtained were in excellent agreement with Stowell's
unified theory for the plastic buckling of columns and plates (NASA TN
No. 1556). This agreement, in addition to that previously obtained for
columns and flanges, is considered a satisfactory experimental verification
of this theory which is based on a deformation theory of Plasticity. Two
other plastic buckling theories of the deformation type and the empirical
ascent-modulus-method also gave a close correlation with the test results,
but a plastic buckling theory of the flow type showed a lack of agreement.

A theory was recently presented in.reference l for the plastic buck-
ling under compression of plates with different conditions of support and
restraint along the unloaded edges. Good experimental verification of the
theory was available at that time for the special cases of plates with the
two unloaded edges free (columns) and of plates with one unloaded edge
free and the other simply supported (flanges). No suitable experimental
data were then available, however, for plates with both unloaded edges
supported.

Various methods have been used to make buckling tests of simply sup-
ported plates in compression. One method utilizes plate-edge support
fixtures. (See, for example, reference 2.) Such fixtures have not always
proved satisfactory because of restraints and supporting conditions devel—
oped along the unloaded edges. A.method.which overcomes this difficulty
and has proved quite satisfactory for the determination of buckling makes
use of seamless square tubes, for which each of the four plates may be
considered simply supported.