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National Advisory Committee for Aeronautics, Technical Notes - Bearing Strengths of Bare and Alclad XA75ST and 24S-T81 Aluminum Alloy Sheet

A report was recently issued covering an inve_stiga—
tion of the bearing properties of the wrought aluminum
alloys commonly used in ai.rcraft construction (reference 1).

Since this Work was undertaken, two new materials, XA758T
and 248—T81, have been developed to the commercial stage
for aircraft use. The object of this investigation was
to determine the bearing yield and ultimate strengths of
these new materials. in the form of bare and alclad sheet.

The test procedure used in_these determinations was
the same as that previously described (reference 1):
Figure l is a photograph of the test _setup. Brie_fly, the
tests involved. loading single thicknesses of O. 064—inch
sheet Zindrh;wide and cut parallel to the dir_elction 6f
rolling, in bearing on a O. 850—inch—diameter s'teel pin.
The proportions of specimens used were the same as found
to be satisfactory in previous tests.’ Measurements bf
the hole elougation were made with a filar micrometer
microsc0pe. Tests were made in triplicate for edge
distances of 1.5,"2, and 4 times the pin diameter.

The material used for these tests was nominally
O. GSA—inch sheet. The 24S—T81 samples were commercial
248— T sheet which had b.een artificially aged-12. hours
at 875°F.

Tensile properties for the material are shown’in
table I. The values given may, with one exception, be
classed as typical. The exception was the Alclad 24S- T81;
for .which the tensile strength was about 1 percent lower
than the tentative minimum value. This difference was
not considered sufficient, however,'to affect the ratios
of bearing to tensile properties determined.

The bearing yield strength values were obtained from
the bearing stress—hole elongation curves shown in figures
2 to 5, using an offset from the initial straight—line
portion of the curves equal to 2 percent of the pin diam—
eter (0.005 in.). Indicated also in table II are the
types of failure obtained. Failures by the tearing out
of— a _porti_on of the sheet above the pin were predominate
for edge distances of 1.5 and 2 _p_in diameters,_ and by _up—
setting or crushing the metal above the pin for edge dis—
tances of 4 diameters.