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National Advisory Committee for Aeronautics, Report - Axial Load Fatigue Properties of 24S-T and 75S-T Aluminum Alloy as Determined in Several Laboratories

In the initial phase of an NACA program on fatigue research,
axial-load tests on 248—513 and 75S—T6 aluminum-alloy sheet
have been made at the Battelle Memorial Institute and at the
Langley Aeronautical Laboratory of the National Advisory
Committee for Aeronautics. The test specimens were polished
and unnotched. The manufacturer of the material, the Alu-
minum Company of America, has made aerial-load tests on
24S—T4 and Wis-T6 rod material. The test techniques used
at the three laboratories are described in detail; the test results
are presented and are compared with each other and with results
obtained on unpolished sheet by the National Bureau of
Standards.

Many engineering structures and all machinery are sub—
jected to repeated loads and are thus potentially liable to
minor or major failures by fatigue. _ As designs become more
refined, fatigue generally changes first from a minor to a
major and costly nuisance and finally may become a domi-
nant design criterion. This stage has been reached for
several classes of airplanes.

Although fatigue research has been pursued for over a
hundred years, it is not possible at present to design against
fatigue failure with anywhere near the same confidence as
against static failure. In order to improve this situation
insofar as possible, the National Advisory Committee for
Aeronautics (NACA) initiated a long-range research pro-
gram about 1947.

This report gives results obtained in a fundamental phase
of the program, the determination of the fatigue properties
of two aluminum alloys (248-T3 and 7SS—T6) ’widely used
for airframe construction. The main purpose of the tests
was to furnish base-line data for succeeding phases of the
program, such as investigations of notch effect and cumula—
tive damage. A large amount of each material (about 5
tons) was purchased at one time in order to minimize the
problem of variation of material properties in subsequent
phases of the investigation.