MIL-DTL-18240F
d. Test the torque values as indicated in 4.4.2, steps e through f, starting with the first
OFF PREVAILING TORQUE. Any torque determined in this test to be in excess
of 150 percent of the maximum prevailing torque values in table II or not meeting
the minimum prevailing torque in table II constitutes failure of this test.
4.4.4 OFF PREVAILING TORQUE at maximum temperature.
a. Assemble the same ten fasteners used in paragraph 4.4.3.
b. Bake the assemblies for one hour to 250°F ±10°.
c. While the fastener is still at 250°F, determine that the OFF PREVAILING TORQUE
value shall not be less than the minimum prevailing torque value listed in table II.
4.4.5 Vibration. Sample nuts and bolts of the size and quantities specified in table III shall
be subjected to the vibration test specified in MIL-STD-1312-7, Vibration. The sample nuts and
bolts shall be assembled to the specified torque in table III and disassembled 4 times, then
reassembled and tested. The fastener assembly shall traverse the entire length of the slots in the
test fixture during the test.
4.4.5.1 Vibration failure conditions. The self-locking element shall have failed the vibration
test for any of the following conditions:
a. When any structural failure occurs in the fastener in the region of the self-locking
element during the vibration test such as a crack intersecting the region of the
threads containing the self-locking element.
b. When any nut rotates greater than 360° during 30,000 cycles.
c. When any nut can be turned completely on or off the bolt or screw, with the fingers,
during or after completion of 30,000 cycles.
4.4.6 Reusability. At the conclusion of the tests specified in 4.4.2 (and 4.4.3 and 4.4.4 for
qualification testing), the test nuts and self-locking fasteners used in this test shall be examined for
damage to the threads. Noticeable distortion or scratches deep enough to reduce the efficiency of
the threads shall be considered a failure of the self-locking element. The threads shall remain in
serviceable condition and permit the installation of a new self-locking fastener or test nut (as
applicable) freely with the fingers up to the self-locking element.
4.4.7 Noncompliance. If a sample fails to pass Group B inspection of table VI, the
manufacturer shall notify the qualifying activity and the cognizant inspection activity of such
failure and take corrective action on the materials or processes, or both, as warranted, and on all
units of products which can be corrected and which are manufactured under essentially the same
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