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National Advisory Committee for Aeronautics, Wartime Report - An Investigation of Sheet-Stiffener Panels Subjected to Compression Loads with Particular Reference to Torsionally Weak Stiffeners

A total of 183 panel specimens of 248T aluminum alloy
with nominal thicknesses of 0.020, 0.025, and 0.040 inch
with extruded bulb~anqle sections of 12 shapes spaced 4
and 5 inches as stiffeners were tested to obtain the buck—
ling stress and the amplitude of the maximum wave when
buckled. Bulb angles from a to 27% inches-ions were test~
ed as pin—end columns. The experimental data are presented
as stress~strain and column curves and in tabular form.
Some comparisons with theoretical results are presented.

Analytical methods are developed that make it possible
for the designer to predict with reasonable accuracy the
buckling stress and the maximum~wave amplitude of the sheet
in,stiffened—panel combinations. The scope of the tests
was insufficient to formulate general design criteria but
the results are presented as a guide for design and an in—
dication of the type of theoretical and experimental work
needed.

This report presents the results of an investigation
on the behavior of sheet—stiffener panels subjected to end
compression.

A short discussion is also given in appendix A of the
preliminary work done on the theoretical calculation of
the stiffener stresses. Further necessary refinements in
the theory are pointed out.

Part II consists of the experimental results obtained
by testing a large number of panels in which the stiffen~
ers were bulb angles of the type commonly used in aircraft
construction. The effective width as a function of the
stiffener stress was determined for panels with stiffen~
ers of various cross sections and torsional rigidities.

The effect of panel length on the failing stress of the
stiffeners, the type of failure, and the panel deformations
were also determined.

A method of determining the buckling stress of the
sheet between stiffeners, y measuring the maximum—wave
amplitude, is given in appendix B.