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National Advisory Committee for Aeronautics, Technical Notes - Static and Impact Strengths of Riveted and Spot Welded Beams of ALCLAD 14S-T6, ALCLAD 75S-T6, and Various Tempers of ALCLAD 24S Aluminum Alloy

Static and impact tests were made on riveted and spot-welded beams
of various high-strength aluminum alloys. The beams of this investiga-
tion were spot-welded before present aircraft specifications for struc--
tural welding became effective. It is evident from radiographic analyses
that the soundness of the spot'welds of this investigation does not meet
these present specifications. In interpreting results, therefore, the
limitations should be considered.

For static loads on riveted beams, the values of modulus of failure
were about the same as tensile strengths for all the alloys except one;
for static loads on spot-welded beams, the values of modulus of failure
were lower than the tensile strengths for all the alloys.

In general, beams of highest-strength materials had the greatest
resistance to impact. The height of drop producing failure of the spot-.
welded beams averaged about 70 percent of that producing failure of the
riveted beams.

No direct relationship seems to exist between the toughness value
of the material as determined from the tensile properties and 'relative
ability to resist impact of the material in the form of a riveted or
welded structure. Aging of beams after assembly is not advantageous and
probably undesirable, at least for spot-welded beams, from the stand-
point. of static and impact strength.

The increased use in aircraft construction of higher-strength
aluminum alloys such as 758-T6 and the various tempers of Eli-S obtained
by artificial aging has made evident the need for information concerning
the behavior of structures of such alloys under static and impact
loading. It seemed. desirable to study the performance of riveted and
spot-welded connections in a structural member subjected to static and
impact beam tests in which the components of the built-up member bend
as a unit and cause the connections to undergo stresses of a different
type from those encountered in tests of simple Joints. Of particular
interest was the comparison of the resistance to tensile rupture of the
various alloys when used in riveted and spot-welded construction. Con-
sequently, the beams were proportioned so as to ensure failure in the
tension cover plate. This required making the compression cover plate
of sufficient thickness to prevent buckling and the web of sufficient
stiffness to preclude buckling due to shear or bending.