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National Advisory Committee for Aeronautics, Technical Notes - Fatigue Strengths and Related Characteristics of Aircraft Joints - II - Fatigue Characteristics of Sheet and Riveted

This paper is a summary of an investigation of the fatigue properties
of sheet and riveted Joints in aluminum alloys. Reports of previous
investigations (references 1 to 5) have given tension-tension fatigue
strengths of 2hS-T Alclad sheet and of spot-welded and riveted lap Joints
in that material. The present investigation was planned to extend these
fatigue studies in the followi respect: (1) the inclusion of other
hi h-strength aluminum alloys,n?2) tests on additional types of Joints,
(3? survey tests of the effects of elevated temperatures on fatigue
properties of the sheet materials and Joints considered, and (h) tests
of fatigue damage-

The experimental equipment and techniques have been described in
detail in preceding reports (see particularly references 1 and 2). In
the present work, the range of stress for some sheet materials was
extended to include some compressive stresses. In these cases, specimens
were restrained from.buckling by the use of "guide plates." (See
reference 6.)

The sections of this paper are developed in the following order:

(1) A description is given of direct-stress fatigue tests of sheet
materials - 2hS-T hare, 2hS‘T Alclad, 75S-T Alclad, R303-T275 bars,
and R303-T275 clad - in the 0-0h0-inch gage. The tests included unnotched
specimens (both transverse and longitudinal), specimens notched by drilled
holes, and specimens with surface scratches-

(2) Results for fatigue tests of riveted lap Joints and riveted
butt Joints with various stiffeners are given, as well as the results <_
of a few tests of multi-arc-welded butt Joints. All Joints were of
0-OhO-inch sheet-

(3) Fatigue test results are presented for specimens of the sheet
materials and for riveted Joints at elevated temperature (375° F).

(M) The results of some tests of cumulative fatigue damage of sheet
materials and of various Joints in these materials are summarized-

In each section, the results of tests are presented with relatively
little discussion. In the CONCEUSIONS test results are recapitulated and
discussed with reference to present knowledge of the fatigue properties
of materials and Joints used in aircraft construction.

This investigation was conducted at the Battelle Memorial Institute
under the sponsorship and with the financial assistance of the National
Advisory Committee for Aeronautics.