MIL-DTL-24640C
a. A micrometer with flat, parallel measurement surfaces on both spindle and anvil, which shall be for the
specimen measurements as specified in 4.7.13.3 and which shall exhibit a measurement error of not more than
±0.0001 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 4.7.13.3. The two jaws shall increase their separation at the uniform rate of 20±2 inches per minute
by means of the tensile machine motor.
4.7.13.3 Procedure. The specimen shall be tested in accordance with ASTM D470.
4.7.13.4 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).
4.7.14 Watertightness. This test shall determine the ability of completed cable, which is intended to pass
through watertight bulkheads, to prevent the longitudinal flow of low-pressure water (see figure 9).
4.7.14.1 Specimen. The specimen shall consist of a 60+2-inch length of completed cable. The specimen shall
be cut to length using a scissors-action cable cutter. (Saws shall not be used.)
4.7.14.2 Special apparatus. Apparatus shall include the following:
a. A source of pressurized water, which shall be provided at a regulated pressure of 27.5±½ lb/in2 and which
shall be for use with the terminal fitting (see (b)) as specified in 4.7.14.3.
b. A metal terminal fitting which applies the source of pressurized water to one end of the specimen, which
supports the requirements as specified in 4.7.14.3, and which shall be fabricated as specified in the following.
Figure 9 shows one possible arrangement for the terminal fitting. The fitting shall admit the specimen end for the
distance specified in 4.7.14.3, and shall have an inside diameter (i.d.), where it fits over the specimen, of not greater
than the measured overall specimen diameter +½ inch. The fitting shall have a means for introducing the source of
pressurized water to the specimen end, and means for bleeding off any air which might be trapped between the
specimen end and the source of pressurized water. The fitting shall also have an aperture for introducing a
hardening sealant (see (c) below), to produce a pressure-tight bond between the fitting and the specimen jacket. A
plug (such as a thick wrapping of rubber tape around the specimen) shall be provided at the place where the
specimen enters the fitting, to prevent sealant loss and to approximately center the specimen within the fitting.
c. A liquid hardening sealant which shall be for producing a pressure tight bond between the fitting and the
specimen jacket, when applied as specified (see 4.7.14.3) and allowed to harden. The sealant shall be at a
temperature of not more than 100 °C when poured into the terminal fitting, and shall not expand in volume while
hardening. An appropriate metal alloy is recommended as a sealant since it can be remelted and reused. Any metal
alloy used shall have a melting point of not greater than 88 °C.
4.7.14.3 Procedure. The specimen shall be secured in a vertical position, the terminal fitting (including the
plug) shall be fitted over its upper end, and the hardening sealant shall be poured through the appropriate terminal
fitting aperture to bond the fitting to the specimen. These shall be done such that the specimen is approximately
centered within the terminal fitting, such that not more than a 6-inch length of specimen jacket is exposed to the
sealant, such that the end face of the specimen is located a distance of not more than 1 inch above the sealant surface
and itself contains no sealant, and such that the aperture through which the sealant was introduced is itself made
pressure tight. The sealant shall be allowed to harden, following which the terminal fitting plug shall be removed or
cut away to the extent that it exerts no radial compression on the specimen. The specimen shall then be positioned
such that it is straight, and such that no portion of the specimen is at a greater elevation than the specimen end within
the terminal fitting. The fitting shall then be connected to the source of pressurized water, and excess air within the
fitting shall be bled off until it can be certain that the entire enclosed specimen end face is exposed to the pressurized
water for the remainder of the test. The source of pressurized water shall remain connected to the fitting for a
continuous period of 6+¼, -0 hours. During this test period, water (if any) leaking from the specimen end opposite
the terminal fitting shall be collected into an initially dry container. Following the test period, the volume of this
collected water shall be measured.
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