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National Advisory Committee for Aeronautics, Technical Notes - Tests on Stiffened Circular Cylinders

Compressive tests were.nade of tWO series of stiff-_
ened circula.r .cylindrical shells under axial load. All_
the shells were 16 inches in diameter by 24 inches in

length and were. rade of aluminun~allov sheet curved to the_ ___—

proper radius and welded with one longitudinal weld. The __
ratios of diameter to thickness of shell wall in the two“
series of specimens were. 258 and 572. Strains were neas~

ured with Hussenoerger tensometers at a number of ease
lines on the stiffeners and shell. The test results are
discussed in the light of published information_on the
subject. 'mfl""

The results of these tests indicate that a spacing _
of circumferential stiffeners equal to 0.57 times the ra~
dius is too great to strengthen the shell wall apprecia—'_
bly. The results are not inclusive enouqh to Show therp~'
timum in stiffener size and spacing for loneitudinal.stiff-'
eners. Plain cvlinders without stiffeners developed ulti~_
mate strengths approximatelv half as great _as_the Buckling
strengths computed by the equation result in“ from the
classical theorv and slightlv greater than those computed ”
by Donnellls large deflection theor;n

In lightweight construction, especially i_n aircraft
and marine. structures, it is quite' comron to use" a stiff
framework covered bv a thin metallic sheet. Under service
loads the thin sheet and the frame act as a unit. “The
condition of the. desiPn mav require either that the shee t
retain its original curvature or degree of initial flat~
uses or .that' the sheet be allowed to develop elastic. _
wrinkles thus throwing most of the load onto the'freme. or
at least causinr a redistri'oution of stress. Sereral
articles in the literature Dive analvses_ of the action _of
seminonocoque structures under certain loading conditions.
(See references 1 to 10.)

Inasmuch as a stiffened cylinder is statically-inde—
terminate to a high dearee under certain conditions, anv
analvtical studv should be checked by tests of representa-
tive structures using the loading conditions treated in
the analvsis. As part of a program of study of the stre ~.lzth
and the stability of thin—sheet construction, tests vere
undertaken bv the Aluminum Research Laboratories for the
study of the distribution of stress in thin~wall struc~
tures. Stif fened flat sheet as well as stiffened circular
cvlinders were subjected to various loading conditions.
The results of bendinP tests on stiffened flat sheet are
discussed in reference 11.