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National Advisory Committee for Aeronautics, Technical Notes - Ultimate Stresses Developed by 2S-T and Alclad 75S-T Aluminum Alloy Sheet in Incomplete Diagonal Tension

Strength tests were made on 2hS—T and Alch 758—513 alumimzm-alloy
sheet in diagonal tension. These tests indicated that the ultimate shear
stress was essentially independent of the rivet factor if the rivet factor
was greater than 0.6, which covers most of the practical range. Curves
showing the effect of diagonal tension on the ultimate shear stress in the
gross section are presenteMese curves supersede those given in
The strength of a shear web is frequently computed on the assumption
that failure occurs when the shear stress in the net section between
rivet or bolt holes reaches the ultimate shear stress of the material.

The main difficulty with this procedure is to find a reallyr satisfactory
method of determining the ultimate shear stress of the material. Another
difficulty is that stress concentration effects of holes may be encountered
at ultimate load similar to those encountered in tension and these effects
must be evaluated. When failure of the shear web occurs before buckling
takes place, the shear load on the web is resisted by true shear stresses.

If failure of the shear web occurs after buckling takes place, the stress
condition in the web is very complicated; however, it is convenient in
strength calculations to use as a reference value a fictitious shear stress
computed on the assumption that the web did not buckle. It then becomes
necessary to find a satisfactory method of determining a fictitious
ultimate shear stress of a thin shear web which fails after buckling occurs
and the relationship between the ultimate shear stress and the degree of
development of buckling.

The most expedient method of determining the ultimate stresses for
shear webs with rivet or bolt holes is by direct tests on shear webs
fastened with rivets or bolts and subjected to a pure shear load. The
stiffening of the webs should be varied in order' to determine the relation-
ship between the ultimate shear stress and the degree of development of
diagonal tension. The ratio of pitch to diameter of the holes should also
be varied in order to evaluate the combined effect of reduction in section
and stress concentration around the holes at ultimate load.