MIL-DTL-8878L
4.6.2 Torsion. A turnbuckle assembly containing the sample component part with a
locking clip installed shall be subjected to the applicable torque load specified in table I, applied
in a clockwise and counterclockwise direction for five complete cycles. The turnbuckle shall
then be disassembled and the sample shall be inspected for evidence of failure per 3.7.2. There
shall be no evidence of cracks in the sample turnbuckle part of locking clip. Deformation of the
turnbuckle or locking clip is acceptable if parts can be disassembled by hand.
4.6.3 Tensile fatigue. A turnbuckle assembly containing the sample component part
shall be subjected to a tension load equal to 60 percent of the MBS specified on the applicable
MS sheet for the sample, applied repeatedly in tension at a rate of approximately one cycle per
second for 300 applications. The turnbuckle assembly shall be disassembled and the sample
parts shall be inspected for conformance to 3.7.3. Elongation of the sample turnbuckle part(s)
shall be determined per ASTM E8/E8M.
4.6.4 Breaking strength. A turnbuckle assembly containing the sample component part
shall be tested for MBS by an appropriate means per ASTM E8/E8M. The MBS value is that
specified on the applicable MS sheet. There shall be no evidence of failure in the sample part. It
may be necessary to fabricate special high strength fixtures for attaching to the parts to be tested
in order to develop the required loads.
4.6.5 Locking clip retention. A locking clip shall be installed in a turnbuckle per the
instructions specified on MS33736. A direct pull of 15 lbs. shall be applied to the locking clip as
shown on figure 1. The locking clip shall not break nor shall the retention feature become
disengaged.
FIGURE 1. Locking clip retention.
4.6.5.1 Functional acceptability. The turnbuckle body and mating terminals must be
assembled and the locking clip inserted in each end of the turnbuckle body. After removing
clips, except for -2, the terminals are rotated one half turn and the locking clip inserted once
again. This functional assembly requirement tests every combination of the locking capability of
the assembly.
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