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between the wires in the bundle to abrade or rub against each other. This may contribute
to the degradation mechanism occurring between mixed or similar wire types. The
introduction of chemicals, dirt, and debris can cause further damage to the EWIS when
this flexure occurs. A flexure test will not be used in this test since it accelerates the
same degradation mechanism as vibration. Flexure on its own may cause differences in
the failure rates due to potential differences in the blocking that may occur within the
conductors. Previous test data has shown that blocked conductor strands, which are
bonded together, dramatically decrease the flex life of the wire. Having an insulated wire
with a tin-coated conductor, which more easily blocks with exposure to high heat, mixed
with an insulated nickel-coated conductor could result in premature failure of the wire.
This is seen as a design flaw and is not specifically related to the interaction of the two
wires. Therefore, testing for this interaction was not included in this test program.
c. Wire-to-Wire Cut Through. Crushing two insulated wires together could cause the
failure of one of the wires preferentially over another. Although this may not be a
common failure mechanism, it does demonstrate differences in the physical
characteristics of the materials.
d. Wire Flexibility. Flexibility of the wires can affect the amount of stress that is imparted
on specific wires within the bundle. Rigid wires have the potential of creating more force
against other components or the structure since it cannot bend out of the way as easily.
Wire with softer type insulations may be more likely to suffer physically when mixed
with more rigid wires. The presence of mixed conductor types may cause the additional
stress to occur between the wires if there is additional stress placed on the bundles, and if
there is to be an alloy conductor wire mixed with annealed copper conductor wire. Since
the alloy does not have the same elongation properties, a disproportionate amount of
stress may be put on the alloy wire, increasing the chance of breakage. Furthermore, the
additional hardness underneath the insulation may cause increased wear on the wire
surface.
B-2
B.3. DESIGN OF TEST PROGRAM.
The performance baseline used the same type wires in the same configuration and under the
same stresses. Simulation testing was performed on the wire properties that are affected by the
mixing of different wire types. The wire types that were focused upon in group I were the
following:
• PVC/glass/nylon
• Wrapped aromatic polyimide (PI)
• Cross-linked polyalkane-imide (XPI)
• Extruded cross-linked ethylene tetrafluoroethylene (XLETFE)
• Mineral-filled and extruded polytetrafluoroethylene (MF-PTFE and PTFE)
• PTFE/glass outer braid
• Wrapped aromatic polyimide/wrapped PTFE composite (PI/PTFE)
• Annealed and alloy conductor
Group II of the test plan incorporated some specific examples of interaction with common
aircraft contamination: hydraulic fluid and metal shavings. Due to the limitations of this effort,
this portion was not extensively tested, but previous data and selected testing was performed to
generate conclusions and recommendations regarding the need for future testing.
The wire bundle samples consisted of a variety of mixed wire combinations using the
aforementioned wire types. The testing concentrated on the properties of the insulation of the
wires, with the failure criteria being the loss of the integrity of the wire insulation, leading to the
potential for direct electrical shorts. The wire-to-wire and bundle tests in tables B-1 and B-2,
respectively, were decided upon for the program, with the concentration being on the wire
bundles since that condition more closely simulates the actual environment of the aircraft.
TABLE B-1. WIRE-TO-WIRE TESTS
Test Purpose
Crush To determine which wire insulation types are most
susceptible to damage. One wire placed over another
perpendicularly.
TABLE B-2. BUNDLE TESTS
Test Purpose
Vibration Periodically perform visual and electrical evaluations to
monitor failures.
Vibration with foreign matter Periodically perform visual and electrical evaluations to
monitor failures.
Vibration with chemical
contamination
Periodically perform visual and electrical evaluations to
monitor failures.
B-3
Vibration testing was performed with the wire bundles clamped onto fixtures that allowed the
testing of 48 bundles concurrently. A vibration profile similar to the one documented in Naval
Avionics Center (NAC) report TR-2333, “Testing of Selected Aircraft Electrical Wire
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