MIL-DTL-24643C
4.8.4.3 Procedure. The ends of the specimen shall be attached to the opposing tensile machine mandrels, such
that each specimen end is tightly wrapped circumferentially around its mandrel for not fewer than two complete
revolutions and then firmly secured at its extremity, to the mandrel. This is to assure that neither specimen nor any
internal components slip during the test. Care shall be taken during specimen mounting to assure that the specimen
shall be subjected only to axial forces and not lateral or torsional forces during the test. The specimen shall be
mounted such that it has free span of not less than 6 inches between its nearest points of contact on the opposing
mandrels at all times during the test. The test shall be initiated by starting the tensile machine motor, thereby
increasing the mandrel separation and applying increasing tension to the specimen. If specimen rupture occurs in a
location other than in the free span between mandrels, the test results shall be considered invalid and the test shall be
repeated using different specimen.
4.8.4.4 Observation. Specimen failure shall be construed if the maximum recorded specimen tension is less
than specified (see 3.1).
4.8.5 Cable aging (260 °C). This test shall be to determine the ability of armored cable with silicone rubber
insulation and jacketing to withstand accelerated heat aging.
4.8.5.1 Specimen. The specimen shall consist of a 48±1 inch length of completed cable.
4.8.5.2 Special apparatus. Apparatus shall include the following:
a. A forced fresh air circulating oven shall be used for supporting the requirements as specified in 4.8.5.3.
The oven air temperature shall be measured in the immediate vicinity of the specimen.
b.
Tensile strength and elongation test apparatus shall be as specified in 4.8.31.
4.8.5.3 Procedure. The specimen shall be bent at the approximate middle of its length to form a symmetrical U
shape, such that its inside diameter (i.d.) shall be six times the specified maximum overall cable diameter (see 3.1)
±¼ inch. The specimen shall be secured in this position using heat resistant twine and shall be freely suspended
vertically such that the specimen ends face downwards within the oven. The air temperature within the oven shall
be raised in a uniform manner from room temperature to a temperature of 260±10 °C over a period of not more than
three nor less than two hours. The oven air temperature shall be maintained at 260±10 °C for a period of not less
than 24 hours and shall then be returned to room temperature. Provision shall be made to catch, for later weighing,
any material which may fall away from the specimen ends during this test. Following the test, the air within the
oven shall be allowed to return to room temperature. The specimen shall then be removed from the oven.
4.8.5.4 Observation. Any of the following shall constitute specimen failure:
a.
The falling away of any material in excess of 1 gram from the specimen ends during the test.
b. Jacket exudation through the armor of an armored cable. (Jacket bulging, without actual flow or cutting, is
not considered to be exudation.)
c.
Jacket shrink-back in excess of
inch from either end of the specimen.
4.8.5.5 Further procedure. If the specimen shows no failure, its jacket shall be subjected to the tensile and
elongation tests as specified in 4.8.31.
4.8.5.6 Further observation. Specimen failure shall be construed if either the jacket tensile strength or
elongation is less than that specified (see 3.1).
4.8.6 Cable aging and compatibility (125 °C). This test shall be performed to detect any significant
degradation due to component incompatibility or prolonged over heating of completed cable containing
thermosetting or silicone rubber and glass tape insulation. This test permits either of two methods (the current
overload method or the hot air oven method) to be used for heat aging.
4.8.6.1 Specimen. Specimens for cable aging and compatibility test shall be as follows:
a.
For the current overload method, the specimen shall consist of a 40±4 foot length of completed cable.
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