MIL-DTL-24643C
4.8.8.3 Procedure. The specimen shall be straightened. If it does not remain straight of itself, it shall be held
straight by securing it (as with twine to a straight wooden bar). The straightened specimen (including wooden bar if
applicable) shall be placed within the refrigeration chamber and subjected to an air temperature of minus 20±2 °C
(unless otherwise specified, see 3.1) for a continuous period of not less than 6 hours. Prior to any change of
chamber temperature, the specimen shall be removed from the chamber (following detachment from the wooden
bar, if applicable) and one specimen end shall be inserted into a clip which has been affixed to (or adjacent to) the
mandrel, such that the specimen is both in contact with the curved surface of the mandrel and also perpendicular to
the mandrel center of curvature axis. The opposite end of the specimen shall then be bent circumferentially around
the curved mandrel surface through an arc of not less than 170 degrees. This bending shall be accomplished at a rate
of not less than 20 degrees per second. The period of time between the removal from the refrigeration chamber and
the completion of specimen bending shall be not greater than 40 seconds. Care shall be taken to avoid heating the
specimen, as by excessive handling, during removal from the refrigeration chamber and during bending. Following
bending, the specimen shall be secured to maintain its bent shape (as with a piece of twine stretch taut and tied
between each end of the specimen) and shall then be removed from the mandrel. Not less than two thirds of the bent
portion of the specimen shall then be dissected and each of its constituent components visually inspected for
deterioration.
4.8.8.4 Observation. Specimen failure shall be construed if the specimen either during bending or upon
dissection and inspection, exhibits distortion or cracking of any specimen component, or exhibits any other visible
deterioration of such a nature or extent as to impair the performance of the cable in service.
4.8.9 Cold bending flexing cable. This test shall determine the ability of completed cable to withstand bending
at low temperature, such as might be encountered during shipboard construction or repair.
4.8.9.1 Specimens. The required specimens shall be as follows:
a. The cable specimen shall consist of a completed cable, which shall have a length of not less than the sum of
12 inches plus 60 times the maximum specified overall cable diameter (see 3.1).
b. Insulated conductor specimens shall consist of not fewer than two different insulated conductors removed
from the completed cable. Each insulated conductor shall have a length of not less than the sum of 12 inches plus
the sum of 30 times the maximum specified overall insulated conductor diameter (see 3.1).
4.8.9.2 Special apparatus. Apparatus shall include the following:
a. A refrigeration chamber for supporting the requirements as specified in 4.8.9.3. The chamber air
temperature shall be measured in the immediate vicinity of the specimen.
b. Two mandrels, as specified in (1) and (2), shall be provided and shall be mounted within the test chamber
such that the axis of each is horizontal and each supports the requirements as specified in 4.8.9.3. Provision shall be
made whereby each mandrel can be rotated about its axis at the rate specified in 4.8.9.3, by an operator located
outside the chamber (as by crank, the shaft of which passes through the chamber wall and mandrel axes to which the
mandrels are affixed, or by remotely controlled and appropriately geared motor, which is located within the
chamber) and whereby each mandrel can be locked in a desired rotational position.
(1) Cable mandrel shall be rigid, smooth cylinder and shall have a diameter of not more than three times
the specified minimum overall cable diameter (see 3.1). The mandrel shall be of suitable length and construction for
the specimen wrapping as specified in 4.8.9.3.
(2) Insulated conductor mandrel shall be a rigid, smooth cylinder and shall have a diameter of not more
than that of the specified nominal insulated conductor diameter (see 3.1) and which shall be of suitable length and
construction for the specimen wrapping as specified in 4.8.9.3.
A magnifying glass which shall provide a magnification of not less than three diameters.
c.
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