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National Advisory Committee for Aeronautics, Technical Notes - Effect of Curvature on Axially Loaded Sheet Stringer Panels

Compressive tests were made on twenty—one 245-T aluminum—
alloy sheet-stringer panels 12 inches in length and 16 inches
in developed width, reinforced by four Z stringers spaced 4
inches apart, The radii of curvature R ranged from 19
inches to infinity, the sheet thicknesses t from 0.025 to
0.190 inch, and the rivet spacing frOm 0.5 to 3 inches.

The curvature increased the strain for buckling of
sheet between stringers up to 5.35 times. The critical
strain for the panels with the heavy sheet covering a range
of values of b3/Rt(b = stringer spacing) up to 6.4 agreed
with the range of values computed from NADA Technical Note
No. 895 for curved sheet with simply supported edges and
with a formula given by Leggett for simple support. The
critical strain for the panels with the thin sheet covering
a range of Values of b2/Rt up to 32. 5 agreed with another
formula by Leggett for clamped support. Panels of interme-
diate thickness covering a range of values of b 2/Rt up to
16 buckled at strains given approximately by Wenzek‘s formu-
la.

The critical strain for buckling between rivets in the
elastic range increased 100 percent with an increase of
balnt from o to 32.

The curvature of the panels generally increased the ef-
fective width after buckling, particularly at strains eIOse
to the buckling strain. At much larger strains the effec—
tive width for the curved sheet approached Marguerre‘s formu—
la for flat sheet with simply supported edges.

Fifteen of the panels failed by stringer instability,
two failed by separation of rivets, three failed by buckling
of stringers and sheet as a unit, and one failed by buckling
of sheet between stringers.

The strength of the panels did not differ by more than
6 percent from that computed from the nomogram in NAGA Tech-
nical Note No. 856 for flat panels of the same design except
for two panels which failed at loads 9 and 15 percent greater
than the computed loads.