MIL-DTL-24643C
b. Circuit continuity monitor. Circuit continuity monitor is a means for continuously monitoring the electrical
continuity of the series through connected specimen conductors, which shall automatically stop the flexing machine
arm (as by removing motor power) when a specimen conductor breaks.
c. Test chambers. Test chambers are chambers for maintaining the specified air temperature within ±2 °C for
accommodating the flexing machine with the specimen attached and for supporting the requirements as specified in
4.8.3.3. The chamber air temperature shall be measured in the immediate vicinity of the upper roller of the flexing
machine. The chamber shall incorporate a viewing port for observing the specimen under test.
Voltage withstand test apparatus. Voltage withstand test apparatus is as specified in 4.9.8.2.
d.
4.8.3.3 Procedure. The flexing machine shall be installed in the test chamber and the specimen installed in the
flexing machine as shown on figure 5. The circuit continuity monitor shall be connected between the two end
conductors of the single series circuit within the specimen. The test chamber doors shall then be closed and the air
temperature within the chamber shall be brought to the specified value within ±2 °C. After the air temperature
within the chamber has been maintained at this value for a period of not less than one hour, the automatic counter
shall be set at zero and the bending endurance test begun by turning on the motor driven flexing machine arm. The
specified number of bending cycles shall be performed. At all times during the test, the air temperature within the
chamber shall be maintained as specified within ±2 °C, and the test chamber doors shall remain closed.
4.8.3.4 Observation. Either of the following shall constitute specimen failure, except the specimen damage
within 2 inches of the location where either specimen clamp had been fastened shall not constitute specimen failure,
but shall require a complete retest using different specimen from the same length of cable:
a. Stoppage of the flexing machine arm caused by the circuit continuity monitor (indicating conductor
breakage), prior to the completion of the specified number of bending cycles. (Loss of conductor continuity from
loss of connectors shall not be construed as failure. If this situation occurs, reconnect connectors and continue
testing).
b.
Rupture of the specimen jacket prior to the completion of the number of specified bending cycles.
4.8.3.5 Further procedure. If the specimen shows no failure, it shall be allowed to return to room temperature
and shall be subjected to the voltage withstand test as specified in 4.9.8, using the specified voltages. Following
this, that portion of the specimen which had been repeatedly bent over the upper rollers shall be dissected. Each of
the constituent components visually inspected for deterioration.
4.8.3.6 Further observation. Either of the following shall constitute specimen failure, except the specimen
damage within 2 inches of the location where either specimen clamp had been fastened shall not constitute specimen
failure, but shall require a complete retest using different specimen from the same length of cable:
a.
Specimen fails the voltage-withstand test (see 4.9.8).
b. Specimen upon dissection and inspection, exhibits visible distortion or cracking of any specimen
component, including strand breakage on any conductor or exhibits any other visible deterioration of such a nature
or extent as to impair the performance of the cable in service.
4.8.4 Breaking strength. This test shall determine the axial tension necessary to break complete cable.
4.8.4.1 Specimen. The specimen shall consist of a piece of completed cable which shall have sufficient length
for use in the test as specified in 4.8.4.3. Additional specimens may be required in the event of invalid test results
(see 4.8.4.3).
4.8.4.2 Special apparatus. Apparatus shall include a motor driven tensile machine, for applying increasing
axial tension to the specimen, which shall automatically indicate within ±1 percent, the maximum axial tension
experienced by the specimen prior to rupture. This tensile machine shall incorporate two parallel and opposing,
rigid and smooth cylindrical mandrels, between which the specimen can be secured, as specified in 4.8.4.3. The two
tension machine mandrels shall increase their separation at the uniform rate of 1± inch per minute during the test
by means of the tensile machine motor.
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