Polyimide has been used extensively as the primary wiring insulation in commercial planes, military aircraft, and space vehicles due to its low weight, high service temperature, and good dielectric strength. New failure modes, however, have been associated with the use of polyimide because of the susceptibility of the insulation to pyrolization and arc tracking. A new wiring construction utilizing partially fluorinated polyimide insulation has been tested and compared with the standard military polyimide wire. Electrical properties which were investigated include AC corona inception and extinction voltages (sea level and 60,000 feet), time/current to smoke, and wire fusing time. The two constructions were also characterized in terms of their mechanical properties including abrasion resistance, dynamic cut through, and notch propagation. These test efforts and the results obtained are presented and discussed

Hammoud, Ahmad N.

Ide, James R.

Muegge, ED

Stavnes, Mark W.

English

NASA Technical Reports Server

NASA Contractor Report 198372
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Performance of Partially Fluorinated Polyimide
Insulation for Aerospace Applications
Ahmad N. Hammoud and Mark W. Stavnes
NYMA, Inc.
Brook Park, Ohio
James R. Ide and Ed Muegge
McDonnell Douglas Aerospace
St. Louis, Missouri
August 1995
Prepared for
Lewis Research Center
Under Contracts NAS3-27186 and NAS1-18580
National Aeronautics and
Space Administration
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https://ntrs.nasa.gov/search.jsp?R=19950026252 2020-06-16T06:22:04+00:00Z

Performance of Partially Fluorinated Polyimide Insulation for
Aerospace Applications
Ahmad N. I-Iammoudand Mark W. Stavnes
Nyma, Inc.
NASA Lewis Research Center
2001 Aerospace Parkway
Brook Park, Ohio 44142
James R. Ide and Ed Muegge
McDonneUDon#asAerospece
P.O. Box 516
St. Louis, MO 63166
Abstract tobeperformed revealed[2].
Polyimide has been used extensively as the primary
wiring insulation in commercial planes, military
aircraftand space vehicles due to its low weight, high
service temperatme and good dielectric strength. New
failure modes, however, have been associated with the
use of polyimide because of the susceptibility of the
insulation to pyrolization and arc lracking. A new
wiring construction utilizing partially fluorinated
polyimide insulation has been tested and
with the standard military polyimide wire. Electrical
properties which were investigated include AC corona
inception and extinction voltages (sea level and 60,000
feet), time/current to smoke and wire fusing time. The
two constructions were also characterized in terms of
their mechanical properties including abrasion
resistance, dynamic cut through and notch propagation.
In this paper, these test efforts and the results obtained
arepresented and discussed.
Introduction
Polyimide based wiring insulation (MIL-W-81381) is
widely used in electrical wiring systems for aerospace
applications due to its high dielectric slzength, low
weight, non-flammability and high temperature
capability. New failure modes, however, have been
rsportedbytheaerospacecommmityin whichdegraded
polyimide insulation becomes conductive upon me
initiation. These failures are detrimental to mission
completion and safety as they have proven to be very
costly in terms of loss of life and expensive
equipment.
An experimental insulation material developed by TRW
under the Air Force's More Electric Aircraft contract,
exhibited some very promising electrical and
mechanical properties for _ applications. This
insulation material uses a partially fluorinated
polyimide (PFPI) formulation and exhibits similar
mechanical and electrical properties to polyimide
material without the arc propagation tendencies. In
work, PFPI insulation was characterized according to
SAE AS-4373 standards in terms of the following:
Corona Inception/Extinction
Wire Fusing Time
Dynamic Cut Through
Weight Loss/Outgassing
Time/Current to Smoke
Abrasion Resistance
Notch Propagation
The NASA test program compared 20 AWG samples of
MIL-W-81381/7 and PFPI insulated wire produced by
TRW. The TRW sample was delivered with a solid
conductor instead of stranded. This reduced the
flexibility of the sample and promoted cracking in the
PFPI layers. Since the PFPI material is in the
developmental stages, the process of applying the
material to the conductor has not been perfected. The
process used to produce the samples permitted air
pockets to form in the insulated layers degrading the
materials performance. The conductor expenmced
tensile stress and flexure during processing which led to
the development of micro cracks forming in the
insulated layers. During the test, extreme care was
taken in the preparation and handling of the PFPI
samples in order to produce reliable results.
A NASA program whose objective is to increase the
safety of _ wiring systems is being managed at
NASALeRC. Theprogram usesa datahaseof testing
information on various candidates to replace MIL-W-
81381, and identifies the requirements which ate
relevant to the NASA missions. Specifically, an
extensive testing database was developed by the Air
Force Wright Laboratory under contract with
McDonnell Douglas Aerospace (MDA) which
thoroughly addressed the aircraft operational
environments [1]. By determining the opea_onal
environments for NASA, as compared to the aircraft
environments, the additional operational requirements
for NASA missions were determined and unique tests
PFPI/MIL-W-81381 Test Results
Corona Inception and Extinction T_'t
A 400 Hz power source was used to determine the AC
corona inception and extinction voltages. Tests were
performed on wire samples that were exposed to
ambient temperature at pressures of sea level and
60,000 feet. Three specimens of each wire sample were
wrapped for 10 equally spaced turns around a 10X
mandrel. Power was applied at a rate of 50 volts per
second until continuous corona discharges were
observed on the positive half cycle of the AC
wavef_rn. After the inception voltage was determined,
the voltage was lowered gradually until the discharges
were no longer detectable and this voltage was recoaled
as the extinction voltage.
Corona results at sea level ae shown in Figure 1 and
results at 60,000 feet are shown in Figure 2. In the
test, the inception and extinction levels for the MIDW-
81381 specimens were consistendy 140 Vans higher
than those of the PFPI construction. The differential
voltage required to extinguish the corona was
comparable for both constructions at 70 Vain.
Iloo
1050
1ooo
95o
9oo
85O
80o
75o
7oo
MIL-W-81381 Inception
MIL-W-81381 Extinction
! !
2 3
SPECIMEN NUMBER
Figure 1.
Level.
Corona Test Results at Sea
700
650
$00
i 550
500
O
450
400
3S0
MIL-Wdl1381 Inlmptlon
MIL-W-81381 Extindlon
I
PFPI Ini:Ipllon
PFPI ExtlnClion
I I
2 3
SPECIMEN NUMBER
Figure 2. Corona Results at Altitude.
Time/Current to Smoke Test
The time/current to smoke test was used to determine
the currentand duration required to Ixoduce smoke from
a finished wire Slx_imen. Six samples of each whe
type were used in this _ The test began by raising
the current through the specimen to I0 amps. Once 10
amps of current was achieved, a stop watch was started.
After 30 seconds, the currentwas increased 5 amps for
an additional 30 seconds. This process was repeated
until smoke was detected.
The results of the fime/cmrent to smoke test are shown
in Figure 3. All of the MIL-W-81381 samples
survived 40 amps. One sample failed at 45 seconds,
four at 50 seconds and one at 55 seconds with the
average being 10.2 seconds at 50 amps. The PFPI
samples did not perfmm as well. Two samples failed at
35 seconds while the other four samples failed at 40
seconds with the average being 0.2 seconds at 40 amps.
It should be noted that the smoke on the MIDW-81381
wire vented out of the seams of the tape construction
while the PFPI constntction vented fixan the bubbles
and imperfections present in the insulation.
35
_so
| 25
_- 20
W15
>
< 5
Figure 3.
Results.
MiL-W-81381
fl P_Pi
35 40 45 5O
CURRENT (A)
Time/Current to Smoke Test
Wire Fusin2 Tune Test
The wire fusing time test was used to determine the
time required to interrupt an insulated wire sample
during an overcurrem condition. Six samples of each
whe type were used in this test. A DC constant current
supply was set for 60 amps which is 2.5 times the
rated cmrent of 20 AWG silver plated copper conchr.mr.
The current was appfied to the specimen and the time to
intenupt was recoaled.
The results of the wire fusing time test arc shown in
Figure 4. The MIL-W-81381 samples averaged 24.8
seconds to intmalpt while the PFPI samples averaged
14.4 seconds. It should be noted that all the samples
tested were fairly cm_istent across the specimen base.
The MIL-W-81381 wire samples averaged 10.4 seconds
longer to intm-upt in the overcurrent condition than dd
the TRW PFPI samples. The PFPI consm_tion
started venting out of the bubbles and imperfections
present in the insulation within a few seconds of power
being applied. The disparity in performance between
the two specimens can be partially atlributed to the
immediate breakdown of the PFPI insulation through
the imperfections and pmti_y due to the u_on of
solid conductor in the PFPI construction.
30,
25,
It.
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O_ 10,
I-
ra 5
I= 0
Figure 4.
MIL-W-..01381 .
PFPI
I I I I I
2 3 4 5 6
9PECIMEN NUUBER
Wire Fusing Time Test Results.
O 600 Et MiL.W.81381500
- -
i 200
_ 100
0
Figure 6.
I 2 3
WEIGHT (LBG)
Abrasion Test Results at 150"C.
Abrasion Resistance Test
The abrasion test was used to provide a relative
abrasion resistance evaluation of wire insulations at
ambient temperature and 150 degrees celsius. Four
samples of each specimen were tested using weights of
one, two and three pounds at each temperatme rating.
Failure was determined by the abrading rod making
electrical contact with the conductor. The number of
cycles to faihue was receded.
The results of the abrasion resistance test at ambient
temperature are shown in Figure 5 and the results at
150 degrees Celsius are shown in Figure 6. At
ambient temperature, the MIL-W-81381 withstood
approximately seven limes more cycles than the PFPI
samples. With a 2 pound weight, the differential was
three times and at 3 pounds the diffezence less than two
times. At elevated temperatures, the MIL-W-81381
withstood eighteen times more cycles as did the PFPI
construction. With both the 2 and 3 pound weights,
the differential was two times. The imperfections in
the PFPI insulation made this test very difficult to
perform. The abrading tool would catch the edge of a
hole or crack and rip the insulation as opposed to
cutting through it. Individual datapoints indicate that
the PFPI conslrucfion has the potential of peafonning
as well as MIL-W-81381 in this test, providing the
imperfections in the insulation are removed.
1::_ r'l PFPI
1 2 3
WEIGHT (LB$)
Figure $. Abrasion Test Results at
Ambient Temperature.
Dynamic Cut Through Test
The dynamiccut through test was used to evaluate the
resistance of the insulation system to penetration by a
cutting surface at various temperatm_. Eight samples
of each wire type were tested for dynamic cut through at
ambient, 70, 150 and 200 degrees Celsius. The cutting
tool was a 20 mil tungsten cable rod with a 4-6 mil
finish. The test concluded when continuity was noted
between the conductor and the cutting tool rod.
Results of the dynamic cut through test are shown in
Figure 7. The MIL-W-81381 samples withstood
approximately twenty percent greater force at each
temperatm'etested. Part of the performance margin cm
be _ to using samded coaducton in the MR.-W-
81381 which permitted some compression of the wire
and produced a greater surface area for the rod to
pmeuate.
.,o,, ]uu,L.w4,,,___
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2$ 71 110 =O|
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Figure 7,
Results.
Dynamic Cut Through Test
Notch Prvva_atlon Test
The notch propagation test was used to evaluate the
ability of a wire insulation to withstand notching or
nicking without propagating the damage down to the
conducts. Six specimens of each sample weae wrapped
around a 0.25 inch mandrel at a rate of 30 revolutions
per minute. One revolution was noted as the winding
and unwinding of the wire in front of and then behind
the notch. Any visual indication of bare conductor was
consideredafailure. After 100cycles,thesamples
weresubmergedin a saltbathfor oneminuteand
subje_edtoa2500volt,60Hzvoltagewithstandtest.
All sixsamplesoftheMIL-W-81381wiresuccessfully
passedthetest. Thebendradiusof 0.25incheswas
toosevereforthePFPIconstruction.Theinsulation
wouldcrack and expose bare conducl_r as soon as the
wire began wrapping around the mandrel. The
insulation in the location of the notch remained in tact.
Mandrel size was increased to determine the Im3p_
bend radius of the construction. With a 0.50 inch
mandrel, the PFPI construction averaged 53 3 cycles
before failure. Two samples broke in half and the
voltage withstand test could not be performed, while
the third sample passed. Cracking was noted away
fi'om the notch on all three samples. Wire Ixeakage
can be attributed to the flexing of the solid conductor
and is not a characteristic of the insulation. With a
0.75 inch mandrel, the three samples su_y
completed the I00 cycle requirement along with the
voltage withstand test.
Wei2ht Loss/Ouumssin2 Test
The weight loss under temperature and vacuum test
was used to determine the weight loss of a
Weconditioned insulated wire when subjected to a
vacuum at temperature. Six specimens of each sample
were _ditioned at 95% relative humidity and 38
degrees Celsius for 72 hours. Another six specimens
of each sample were preconditioned at less than 5%
relative humidity and 38 degrees Celsius for 72 hours.
After preconditioning, the samples were weighed and
placed in a temperatm'e altitude chamber preconditimed
to 200 degrees Celsius. The chamber was sealed and
pressure was reducedto 33 Tc_r fc_ 384 hours. At the
completion of the 384 hours, the specimens w_e
removed and weighed to acquire a weight loss
(outgas_g) value.
2.00%'
,J
.t!'°°"
_ 0.50%
L
0.00%
B MIL-W-81381
0 PFPI
t,
RELATIVEHUWDITY
Figure 8.
Results.
Weight Loss/Outgassiug Test
The weight lnss/outgassing results are shown in Figure
8. The PFPI insulated wire demonslxat_l a 0.9%
greater weight loss than did the MIL-W-81381. Based
on the percentage of weight gain/loss present in the
PFPI material after preconditioning, moisture which
was trapped in the imperfections of the insulation
coating, was released during the test skewing the
results.
Conclusions
The tests performed to date demonstrated the similar
perfc_nance characteristics bexween MIL-W-81381 and
PFPI insulations in the areas of AC corona inception
and extinction and dynamic cut through. The MIL-W-
81381 consuuction outperformed the PFPI cons_
in the areas of wire fusing time, time/current to smoke,
abrasion resistance, notch propagation and weight
loss/outgassing. Based on the results of this
evaluation, the present pmccss of applying the PFPI
coating to the conductor must be improved prior to
conducting additional testing. The PFPI matea_
demonstrated many outstanding qual/ties during this
evaluafim, but the presence of voids and imperfections
in the PFPI coating negatively impacted its overall
performance. Future evaluations of the PFPI material
should focus on casting films which can he used in a
multiple tape insulation construction.
Acknowledgment
The authors would like to thank Dr. Daniel R.
Mulviile, Director of NASA HQ OS&MA, Technical
Standards Division for his continuedsupport and
technical guidance. The testing effort was performed by
McDonnell Douglas Aerospace under contract NAS1-
18580, Technology for Hyperspa_ Vehicles - Task #12
Feasibility Study of New Wire Insulation
Constructions for NASA Aerospace Wiring
Applications. Work was also peffmned trader contract
NAS3-27186.
References
o Soloman, R., Woodford, L., Domalewski, S., New
Insulation Constructions for Aerospace Wiring
Applications, McDonnell Douglas Aircraft
Company, June 1991, WL-TR-91-4066.
. Stavnes, M.W., Hammoud, A.N., NASA
Requirements and Application Environments for
Electrical Power Wiring, Sverdrup Technology,
Inc., August, 1992, NASA CR-191064.

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August 1995 Final Contractor Report
4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Performance of Partially Fluorinated Polyimide Insulation for Aerospace
Applications
6. AUTHOR(S)
Ahmad N. Hammoud, Mark W. Stavnes, James R. Ide, and Ed Muegge
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
NYMA, Inc.
NASA Lewis Research Center
2001 Aerospace Parkway
Brook Park, Ohio 44142
and
McDonnell Douglas Aerospace
P.O. Box 516
St. Louis, Missouri 63166
I. SPONSORING/MONITORINGAGENCYNAME(S) ANDADDRESS(ES)
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
WU-297-50--00
C-NAS 3-27186
C-NAS 1-18580
8. PERFORMING ORGANIZATION
REPORT NUMBER
E-9820
q0. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA CR-198372
11. SUPPLEMENTARY NOTES
Prepared for the 1995 Conference on Electrical Insulation and Dielectric Phenomena, sponsored by the IEEE Dielectrics and Electrical
Insulation Society, Virginia Beach, Virginia, October 22-25, 1995. Abroad N. Hammoud and Mark W. Stavnes, NYMAInc., 2001
Aerospace Parkway, Brook Park, Ohio 44142 (work funded by NASA Contract NAS3-27186); James R. Ide and Ed Muegge,
McDonnell Douglas Aerospace, P.O. Box 516, SL Louis, Missouri 63166 (work funded by NASA Contract NAS1-18580). Respon-
sible person, Ronald Cull, organization code 5430, (216) 433-3948.
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13. ABSTRACT (Maximum 200 words)
Polyimide has been used extensively as the primary wiring insulation in commercial planes, military aircraft and space
vehicles due to its low weight, high service temperature and good dielectric strength. New failure modes, however, have
been associated with the use of polyimide becauseof the susceptibility of the insulation to pyrolization and arctracking.
A new wiring construction utilizing partially fluorinated polyimide insulation has been tested and compared with the
standard military polyimide wire. Electrical properties which were investigated include AC corona inception and
extinction voltages (sea level and 60 000 feet), time/current to smoke and wire fusing time. The two constructions were
also characterized in terms of their mechanical properties including abrasion resistance, dynamic cut through and notch
propagation. In this paper, these test efforts and the results obtained are presented and discussed.
14. SUBJECT TERMS
Polyimide insulation; Space wiring; Corona
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Performance of Partially Fluorinated Polyimide Insulation for Aerospace Applications

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