23
Flammability Properties of Aircraft Carbon-fiber Structural Composite J. G. Quintiere, U of MD R. Walters, S. Crowley, FAA
Flammability Properties of
Aircraft Carbon-fiber
Structural Composite
J. G. Quintiere, U of MD
R. Walters, S. Crowley, FAA
Composite Material
• Consider Material BMS 8-276, Toray Composites (America)• Carbon fiber density = 1750
kg/ m3
• Volume fraction of carbon in the composite = 0.60
• Resin density = 1220 kg/ m3
• Char fraction (typical) of resin alone in flaming combustion = 0.25
Facsimile to Boeing 787
• No surprises in the performance of a new material
• Measure basic flammability performance
• Establish data and properties to explain fire scenario hazards
Objectives
• Measure fire behavior over range of heat flux, to 100 kW/m2
• Establish behavior and limits • Ignition
• Flame spread
• Burning rate
• Carbon smoldering
• Determine properties useful in modeling
Properties
• Thermal conductivity
• Specific heat
• Heat of decomposition
• Kinetics
• Combustion
Thermal Conductivity
k =′ ′ Ý q δ
∆T
Power = VI
T2-T1
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 100 200 300 400 500 600 700
k = 0.023 xT(ºC)0.46, R = 0.95
k W
/m-K
Temperature ºC
DecompostionRange
of Resin
Compositeoriginal
composition
MostlyCarbonFiber
composition
~ -20% errorDue to heat losses
Thermodynamic properties
0
5
10
15
20
25
30
0 100 200 300 400 500 600
Cp
Eff
ecti
ve S
pecif
ic H
eat,
Cp
(J/K
-g o
rig
inal)
Temperature (°C)
Heat of DecompositionArea under curves shaded
2.07, 2.22, 3.12 kJ/gAverage = 2.5 +/-0.5 kJ/g
Specific Heats per original mass
original CP = 0.75 +0.0041 T (ºC) J/K-g original
residue, CP,O
= 0.84 +0.0035 T (ºC) J/K-g original • Specific heat
• Heat of decomposition
• By DSC
Decomposition properties
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
160 240 320 400 480 560 640 720
TGA data and theory Data
Model
Ma
ss
Fra
cti
on
(--
)
Temperature (°C)
1°C/min
30°C/min3°C/min
10°C/min
Residue fraction, Xc = 0.74
• By TGA
• First order Arrhenius
(1 )( )
(1 )c
dk T
dt X
α α−=
−
1
1i i
f i c
mm m m
m m Xα
−−
= =− −
aERT
pk a e
−
=
E = 182 kJ/mol ap = 9.67 x 1010 s-1
Ignition: by radiation
0
50
100
150
200
250
300
350
0 20 40 60 80 100 120
Ignition
Pilot smoothPilot roughAuto rough
tig= 2x10
4 * q"
-1.5) R= 0.99
tig= 3x10
4 * q"
-1.6) R= 0.98
tig= 23x10
5 * q"
-2) R= 0.97
Tim
e (
s)
Incident Heat Flux (kW/m2)
Auto
&
Piloted
Burning: Cone Calorimeter
0
50
100
150
200
250
0 100 200 300 400 500
Incident Heat Flux: 25 kW/m2 Rough 1
Smooth 1
Rough 2
Smooth 2
HR
R (
kW
/m2)
Time (s)
Avg. Peak130 +/- 30
0
50
100
150
200
250
300
350
0 100 200 300 400 500
Incident Heat Flux: 50 kW/m2
Rough 1
Smooth 1
Rough 2
Smooth 2
HR
R (
kW
/m2)
Time (s)
Avg. Peak250 +/- 50
0
50
100
150
200
250
300
350
400
0 100 200 300 400 500
Incident Heat Flux: 75 kW/m2
75R1
75S1
75R2
75S2
75R3
HR
R (
kW
/m2)
Time (s)
Avg. Peak290+/-40
0
50
100
150
200
250
300
350
400
0 100 200 300 400 500
Incident Heat Flux: 100 kW/m2
100R1
100S1
100R2
100S2H
RR
(k
W/m
2)
Time (s)
Avg. Peak315+/- 40
Average Burning Rate
0
50
100
150
200
250
300
350
0 20 40 60 80 100 120
Peak Average for all data
HRR= 76.8 + 2.87q" R= 0.93
Avera
ge P
eak H
RR
(kW
/m2)
Incident Heat Flux (kW/m2)
OSUvertical
HRP = 2.87
Heat of Combustion ~ 20 +/- 3 kJ/g-vapor
L = 7.0 kJ/g-vapor
Xc = 0.74 g residue/g-original
hg = (7.0)(1- 0.74) = 1.8 kJ/g-original
HRR crit,b
Heat of Combustion
0
5
10
15
20
25
30
0 20 40 60 80 100 120
Heat of Combustion(based on overall average for flaming)
∆h
c k
J/g
vapor
Incident Heat Flux kW/m2
Burning in OSU Calorimeter
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.Jet-like flames
Overall Burning
0
5
10
15
20
25
30
35
40
0 20 40 60 80 100 120
Total Heat Released based on Flaming
smooth rough
TH
R (
MJ/m
2)
Incident Heat Flux (kW/m2)
CHF (pilot ignition) ~ 18 kW/m2
But can continue flaming to ~ 8 kW/m2
Smoldering
• After flaming, smoldering can continue
• Blue flame also possible
• Energy rate ~
5 – 35 kW/m2
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120
Estimated Burn Rate of Carbonat end of Cone Tests
Bu
rn R
ate
(g
/m2-s
)
Incident Heat Flux (kW/m2)
Blue CO flame seen
Temperatures in smoldering
0
200
400
600
800
1000
0 20 40 60 80 100 120
Carbon temperature following Flaming
Surface TemperatureFlux Blackbody Temperature
Su
rface T
em
pera
ture
(ºC
)
Incident Heat Flux (kW/m2)
Convection + conduction lossesminus energy of smoldering
Morphology of residue
FIGURE 19A. AFTER BURNING FRONT AND BACK, 8.2 kW/m2
FIGURE 19F. AFTER BURNING FRONT AND BACK, 85 kW/m2
Morphology properties
0
0.5
1
1.5
2
2.5
0 20 40 60 80 100 120
Morphology of degradation
Porosity fraction, final
Final Vol./ Initial Vol.
Final thickness to original @ center
Resin and its Char fraction, final
Fra
cti
on
Incident Heat Flux (kW/m2)
char fraction expected
char oxidized
resin remains
Volume expansion
Thickness expansion
Final Porosity
Resin and char Char fraction of Resin ~ 0.25
Residue Fraction: carbon+
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0 20 40 60 80 100 120
Final Residue FractionCarbon fibers + Resin char
Cone Tests
Fra
cti
on
of
Mass R
em
ain
ing
Incident Heat Flux (kW/m2)
TGA result
Flame Spread
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Flame Spread Results
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20
Spread Rate
UpwardDownHorizontal
Velo
cit
y
mm
/s
Heat Flux kW/m2
No hor. spread No down spread
Upward
CH
F
Concluding Remarks
• Properties determined for predicting hazards
• The sample can swell to over twice its volume, and its porosity after burning is about 65 %.
• The minimum heat flux required • for auto-ignition is 32 kW/m2,
• for piloted is 18 kW/m2, and
• for burning is about 10 kW/m2.
• Flame spread will occur for heat fluxes below 18 kW/m2
after pre-heating for 4 minutes
• The remaining carbon fiber can smolder
End
