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National Advisory Committee for Aeronautics, Technical Notes - Investigation of Static Strength and Creep Behavior of an Aluminum Alloy Multiweb Box Beam at Elevated Temperatures

The results of an investigation to determine the static strength and
creep behavior at elevated temperatures of seven nominally identical
multiweb box beams made of ZAS-TB aluminum alloy are presented. The
methods that were used to predict failure stresses in the static—
strength tests were in good agreement with the experimental results.
Creep deflections and creep lifetimes are presented for beams subjected
to constant loads and to various heating conditions. Lifetime is sat-
isfactorily predicted from material stress—rupture data when tensile
failure occurs at both constant or varying temperatures.

Determination of static strength and creep behavior of fabricated
structures subjected to elevated temperatures is a problem of impor—
tance in the design of aircraft. Room-temperature static strength of
fabricated structures such as box beams can be estimated from methods
of the type outlined in reference 1. Although these methods may be
used to estimate elevated-temperature static strength of box beams, the
results have not been verified experimentally.

At present, no methods are available for predicting creep behavior
of fabricated structures. Studies have been made to obtain procedures
for determining creep behavior of structural components such as columns,
stiffened panels, and solid-section beams (for example, refs. 2 to A);
however, extension of these procedures for application to box beams has
not been made. The prediction of creep behavior of fabricated struc-
tures is a complex problem for which approximate or empirical solutions
may be most practical. In any case, the prediction of creep behavior
should be guided and confirmed by experimental data.

In the present paper, a study is made of the results obtained from
static-strength and creep tests at room temperature and elevated temper-
atures of seven nominalky identical multiweb box beams of 248—T5 alum- '
inum alloy. Static strengths are determined from procedures given in
references I, 5, and 6 and are compared with the experimental data.
Tensile and compressive failures of the box beams are predicted in the,
staticpstrength tests for different temperatures and different exposure
times.