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XPI and MF-PTFE (see figures 47 and 48).
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FIGURE 47. MODERATE WEAR OF XPI
AND PI/PTFE FROM STRAP IN
GROUP IIF
FIGURE 48. MODERATE WEAR OF
PI/PTFE FROM STRAP WHEN MIXED
WITH MF-PTFE IN GROUP IIF
5.2.5.1.2 Group IIM.
Table C-11 in appendix C shows that none of the bundles with metal shavings exhibited
moderate or severe wear from the straps. Only the PI/PTFE wire (code 10) had slightly more
wear when mixed with PI, XPI, XLETFE, MF-PTFE, and PTFE/glass (codes 2, 3, 4, 7, and 9,
respectively) than in the nonmixed condition.
5.2.5.2 Wear From Lacing String.
5.2.5.2.1 Group IIF.
Of the fluid-soaked bundles, only the PI wires (code 2) exhibited wear from the lacing string (see
figure 49 and appendix C, table C-12). A little wear was noted for the nonmixed bundle,
whereas moderate wear was noted when mixed with MF-PTFE.
5.2.5.2.2 Group IIM.
Of the metal contaminated bundles, the MF-PTFE wires (code 7) were the only ones that showed
slight wear from the lacing string. The metal shavings themselves may have induced this wear
by lodging between the wire and string.
5.2.6 Wire Wear From Vibration Fixture.
One PI/PTFE wire (code 10), in a bundle mixed with PI/PTFE alloy wire (code 11) and
contaminated with metal shavings, failed wet electrical testing. This bundle did exhibit some
wear from the plate, and some wire-to-wire wear, but the cause of the failure could not be
determined. A small mark, possibly a burn mark, was noted in an area that was inside a clamp,
so it is possible that a metal shaving penetrated the insulation, weakening the insulation system.
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FIGURE 49. MODERATE WEAR ON PI FROM LACING STRING WHEN MIXED
WITH MF-PTFE IN GROUP IIF
5.2.7 Wear on Support Components.
The clamps were the only support components that exhibited wear with a moderate or severe
rating, and in all but one case, one of the wire types was PVC/glass/nylon, MF-PTFE, or
PTFE/glass. The one case that did not include one of those wire types was the nonmixed bundle
of PI/PTFE alloy wires, which caused severe damage to the clamp.
The straps exhibited only slight wear from several of the wire combinations, but the lacing string
did not appear to cause wear on any of the wires in the bundles.
5.2.8 Wear of Single Wires Versus Twisted Pairs.
It was noted that the same number of wet electrical failures were detected on twisted pairs as on
single wires in group II.
5.3 TEST GROUPS I AND II COMPARISON.
The results indicate that in the mixed wire bundles, moderate wire-to-wire wear occurred on
more bundles contaminated with hydraulic fluid than with metal shavings. This condition was
most pronounced on the PI and XPI wire types (codes 2 and 3, respectively). One explanation
for this may be that many of the metal shavings in the unrestricted sections of the bundles fell out
of the bundles during vibration conditioning. Another explanation may be that in the areas of the
clamps, tie straps, and lacing string, the wires were restricted enough to prevent significant
movement and interaction of the wires against the metal shavings. Still another could be that the
hydraulic fluid, by swelling the insulation surface and softening the insulation, thereby reduced
the resistance to abrasive forces during vibration.
Some wire combinations in groups II exhibited slipping in clamps after 100 hours of vibration,
whereas no slipping was noted for the same combinations in group I after the same vibration
conditioning.
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The number of mixed wire bundles that showed more damage than the associated baseline
bundles was greater in groups II than in group I; however, most of the combinations displaying
this characteristic were different in groups I and II. There was more similarity between groups
IIF and IIM.
Seventy-seven percent of the group I bundles did not slip in the clamps after 100 hours of
vibration exposure, whereas the numbers for groups IIM and IIF were 38% and 25%,
respectively.
In both groups I and II, the sections of the wire bundles that were mounted to stationary plates
did not exhibit notable wire or clamp damage.
5.4 GROUP III CRUSH TEST RESULTS.
The crush test performed was a variation to the dynamic cut-through test that is define in SAE
AS4373, method 703 [5]. In this crush test, a defined load was applied to compress two
perpendicular wires, rather than compressing a blade against a single wire. The hardness of the
second wire directly affects the amount of damage suffered by the first wire.
The testing was performed on the same 24 wire combinations as selected for group II. The
complete results from the test are provided in appendix C, table C-13.
The results indicate that for the wire combinations tested, the MF-PTFE wire (code 7) always
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