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National Advisory Committee for Aeronautics, Technical Notes - Effect of Rivet Pitch Upon the Fatigue Strength of Single Row Riveted Joints of 0.025 to 0.025 inch 24ST Alclad

This investigation was conducted to determine the ¢~~
effect of rivet pitch upon the fatigue strength of sinélg— 'w a
row lap joints of 0. 025_ to O. 025- inch' 24S—T alclad, using' " ’"
One—eighth AK430 round—head rivets. A further object was
to determine the variation of the effectivé- stress concen— . :l:
tration factor in fatigue as a function bf rivet pitch and '
of load per rivet.

Single—row lap—joint fatigue specimens were fabri-
cated from 0 025-inch 248-? alclad sheet, using AN43ODD—4
rivets. The specimen dimensions and the rivet pitches_h_ .flu.1,w
are indicated in figure_ 4. The allowable_ design load for -m
AHéSODD—e rivets in 0.025 24S—T alclad sheet is 256 _pounds_
per rivet (ANCeS).

Because of a typographical error in ordering speci—
mens, the AN430 rivets were specified as the DD type in-
stead of the AD type. Failure always occurred in the
sheet, however, and check tests made with two specimens
using AD—type rivets agreed closely with results for
specimens using DD—type rivets.

All fatigue specimens were tested at 1800 cycles per
minute in the Lockheed vibrating beam machines, one ofi
which is shown in figure 1. Tests were conducted at an
R value of"0.2 (R; the range ratio, is the algebraic
ratio of minimum to maximum load).

The dynamic load was measured—by means of an elec—
trical strain gage bridge, installed 0n the upper speci—
men mount as shown in figure 2. This bridge was stati—
cally calibrated before-each teat-by means of dead weights
applied at known distances from the beam pivot and the
specimen center line. A percentage—of—nodulation meter,
used as a peak voltmeter, measured the bridge unbalance;
and the bridge unbalance corresponding to the known static
load was duplicated by the maximum and minimum peaks under_
dynamic loading.

All static tension tests were conducted in the
300.000—pound Southwark—Emery testing machine in the
Triplett and Barton laboratory. Load-deformation and
load—permanent—deformation curves were obtained, using
two dial gage extensometers over a 3.2—inch gage length
across the joint as shown in figure 3.