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National Advisory Committee for Aeronautics, Technical Notes - Strain Measurements and Strength Tests of 25'' Diagonal Tension Beams of 75S-T Aluminum Alloy

A series of diagonal—tension beams were tested to
determine the accuracy of previously published design
charts and formulas for beams of ZMS-T aluminum alloy
when used to analyze beams of 7BS-T aluminum alloy.
Strain measurements were made to determine the stresses
in the uprights of the beams and to determine the ulti-
mate stresses that could be developed in the uprights.
The predicted stresses were in fair agreement with the
experimental stresses or.were conservative. The ulti—
mate stresses that could be developed in the beams were'
in agreement with stresses predicted_by previously pub-
lished formulas except for the stresses developed in the
uprights,which failed by forced twisting. For these
uprights, the developed stresses were greater than those
given by previously published .formulas derived from tests
of beams of 2&3- T aluminum alloy.

A semiempirical theory for the action of shear webs
in incomplete diagonal tension with design charts that
facilitate the use of themtheory and design formulas for
estimating allowable stresses is presented in reference l,
More refined design charts and design formulas are given
in reference 2. Empirical coefficients obtained from
tests of beams of ans-T aluminum alloy are employed in
the design charts and in some of the design formulas,_um4;
These coefficients may depend upon certain material
properties and, because the new high—strength 758— —T alu—
minum alloy is now being used in aircraft structures, it
was desirable to test beams of 753— —T aluminum alloy in
order to determine whether the charts and formulas of
reference 2 were applicable to these beams. Such beams
were tested in the Langley structures research laboratory
and the results are herein presented.

The test specimens consisted of eight beams of the
general dimensions shown in figure l(a).- Detailed dimen-
sions for each‘bemn are given in table 1, and dimensions
of the cross section of the uprights for each beam are _
given in figure l(b). The web and_uprights were_fastened"“
to the flanges as diagrammed in figure 1(a) for_the beams
with single uprights. _For the beams_With double uprights,
the web was placed between the flange angles and the
uprights were joggled at each flange. The webs and the
intermediate uprights were of Alclad'TSS-T aluminum alley:'
and the flanges and the loaded uprights were of abs-T alu-
minum alloy.