MIL-DTL-24643C
4.8.19.3 Procedure. Specimens shall be maintained at ambient temperature for a period of not less than 30
minutes immediately prior to accelerated aging. Accelerated aging procedures shall be performed as follows, using
one specimen. Each specimen shall be freely suspended vertically, secured by one end, within the oven. The air
temperature within the oven shall then be raised to the value specified in table XII, and shall be maintained at this
value for a continuous period of not less than that specified in table XII. Each specimen shall then be removed from
the oven and tested as specified in 4.8.30.
TABLE XII. Details for accelerated aging procedures.
Temperature
Minimum period
Specimen material
Procedure
(°C)
(hours)
Insulation specimens
Thermoset
Air oven
121±2
168
Polyethylene
Air oven
100±2
48
Jacketing specimens
Silicon rubber
Air oven
260±2
24
Cross linked-polyolefin
Air oven
136±2
168
4.8.19.4 Observation. Any of the following shall constitute specimen failure:
a.
A specimen tensile strength which is less than that specified (see 3.1).
b.
A specimen elongation which is less than that specified (see 3.1).
4.8.20 Tear strength. This test shall determine the ability of elastomeric jacketing material to withstand the
propagation of a cut passing through a portion of its length.
4.8.20.1 Specimen. This test shall consist of a piece of jacketing material, which shall have been cut to the
dimensions specified in ASTM D470. Specimens shall be removed from completed cable. Not fewer than five
specimens shall be required.
4.8.20.2 Special apparatus. Apparatus shall include the following:
a. A micrometer with flat, parallel measurement surfaces on both spindle and anvil, which shall be for the
specimen measurements as specified in 4.8.20.3 and which shall exhibit a measurement error of not more than
±0.001 inch.
b. A motor driven tensile machine which shall be for applying increasing tension to the specimen, and which
shall automatically indicate within ±1 percent the maximum tension experienced by the specimen prior to tearing.
This tensile machine shall incorporate two parallel and opposing jaws, between which the specimen can be secured,
as specified in 4.8.20.3. The two jaws shall increase their separation at the uniform rate of 20±2 inches per minute
by means of the tensile machine motor.
4.8.20.3 Procedure. The specimen shall be tested in accordance with ASTM D470.
4.8.20.4 Observation. Specimen failure shall be construed if the median value of the measured tear strengths of
all specimens is less than that specified (see 3.1).
4.8.21 Twisting endurance. This test shall determine the ability of completed cable, which is intended to be
flexed during use, to withstand repeated and reversing torsional motion while subjected to a specified temperature.
4.8.21.1 Specimen. The specimen shall consist of a piece of completed cable which shall have a length of not
less than the sum of 18 inches plus 10 times the specified maximum overall cable diameter (see 3.1), except that no
specimen shall have a length of less than 24 inches. Specimen circuit is formed by the conductors. The two end
conductors of this series circuit shall be connected as specified in 4.8.21.3.
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