• Version
• 68 Downloads
• 732.78 KB File Size
• 1 File Count
• November 25, 2016 Create Date
• November 25, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Strain Measurements on Small Duralumin Box Beams in Bending

Extensive strain—gage measurements were made chiefly
on the tension side of five small rectangular bourbeams‘"
constructed of sheet duralumin. The main conclusioh has”
that within the test range the tension cover may'be con~
sidered as being fully effective but that at any given
point on the beam there may be unaccountable vafiatione of
5 oercent from the calculated stresses'afi the thicker
sheets tested (0.044 and 0.023 inch) and of 1C percent or
more on the thinnest sheet tested (0.014 inch).

Present—day airplane construction is characterized by
thin— walled built— —up structures. Experience has shown
that established and tested formulas for st_rength of struc—
tures do not always give the required degree of aCcufaoy
when applied to such airplane structures. The reasofififbr
these discrepancies is that some of the fundamental assump—
tions of the theory are not fulfilled so well as they are
in the more solid structures used in other branches of en—
gineering.

One of the points in question is the beam action of
thin shells. The engineering theory assumes that plane'
cross sections remain plane and that no changes in Shape
of the cross sec't ions occur owing to loading or, if they
do occur, that they may be neglected. In beams'consisting
of thin shells it has been found, however, that these
changes may not be negligible in some cases.

It therefore seems highly desirable to check experi~
mentally how valid the usual formulas are when applied_to
various types and sizes of box beams. The present inves—
tigation deals with fairly small box beams of rectangular
section.

The tasts Were made of 178T aluminum—alloy beams.
The important (nominalJ dimensions of these beams are
given in figure 1; this figure also indicates fichemati- "
cally the jig used for attachingmthe beams to a heavy col—
umn.