parameters for the thermal decomposition of epoxy resin/carbon fiber composites in cone calorimeter...
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Parameters for the thermal decomposition of epoxy resin/carbon fiber composites in cone calorimeter
4th ICHS Conference, September 14, 2011
D. Quang DaoJ. Luche, F. Richard T. RogaumeC. Bourhy-Weber S. RubanL. Bustamante Valencia
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 2Public
Epoxy resin/carbon
fiber composite wall (few cm)
ContextThe high-pressure (70 MPa/10.1 kpsi) fully wrapped
epoxy resin/carbon fiber composite cylinder is currently the preferred option for fuel cell electric vehicle
Epoxy resin/carbon fiber composite cylinder
Liner: H2 tightness (few mm)
CostCostGravimetric
capacity
Gravimetric capacity
Volumetric capacity
Volumetric capacity
Light weight Excellent mechanical performance
High capacity of H2 storageGood chemical and electrical resistance
H2 vehicle refilling station
Type 2Type 1 Type 4Type 3Type 2Type 1 Type 4Type 3
Cylinder connector
Fire safety strategy: preventing the cylinder from bursting
Releasing hydrogen through a thermal pressure relief device and/or using a thermal protection
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 3Public
Objective
To optimize the design of the fire protection of the cylinder by improving the understanding of the thermal behavior of the epoxy resin/carbon fiber composites
The thermal behavior is influenced by (Pilling et al.):Decomposition temperatureCarbon fiber fraction Nature of carbon fiber
Experiments showed:
CF fraction & temperature
Conductivity & decomp. rate
Fire resistance of composite
The thermal parameters such as mass loss, mass loss rate, piloted ignition time, thermal response parameter
and temperature of ignition are investigated
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 4Public
Materials studied
The epoxy resin/carbon fiber composites are pre-impregnated bands of commercial references
Two representative references are tested:56 vol% Carbon fiber59 vol% Carbon fiber
Results of elementary analysisElement Epoxy resin
Composite 56 vol% CF
Composite 59 vol% CF
C 70.1% 81.6% 84.6%O 17.0% 6.6% 5.4%H 8.7% 4.6% 2.9%N 3.1% 5.1% 5.4%
Water 1.1% 0.5% 0.3%Total 100% 98.4% 98.6%
Thermal property Value
Density (r) 1472 ± 20 kg.m-3
Specific heat capacity (Cp) 0.9 kJ.kg-1.K-1
Thermal diffusivity parallel to CF (α) 2.75 ± 0.10 mm2.s-1
Thermal diffusivity transverse to CF (α) 0.40 ± 0.04 mm2.s-1
Thermal conductivity parallel to CF (λ)a 3.30 ± 0.30 W.m-1.K-1
Thermal conductivity transverse to (λ)a 0.48 ± 0.05 W.m-1.K-1
a Calculated from the heat capacity and the diffusivity
Thermal properties measured
These results are key to understand the fire behavior of the composite samples
The carbon fiber fraction [vol%] is determined experimentally by the acid attack method:
1. Density measurement of the virgin composite
2. Resin dissolution in sulfuric acid +H2O2
3. Mass measurement of the fibers (known density)
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 5Public
HORIBA PG250 IRTF
13
HORIBA PG250 FTIR
13
Cone calorimeter experiments
Heat fluxes: 14-75 kW.m-2
Spark ignition was usedAtmosphere: airTest procedure: ISO 5660
100 ± 0.5 mm long × 100 ± 0.5 mm wide × 10.1 ± 1.5 mm thick
Composite Masses56 vol% CF 171.2 ± 2.8 g59 vol% CF 148.7 ± 1.8 g
Sample masses
Measurements:Mass lossMasse loss rate (MLR)
Piloted ignition time (tig)In-depth temperature
Two k-type thermocouples in-depth
Composite samples
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 6Public
Ignition time and critical heat flux (CHF)
Where:
qe: Heat flux [kW.m-2]
Tig, T: Ignition and ambient Temp. [K]: Thermal conductivity [kW.m-1.K-1]r: Density [g.m-3]
Cp: Thermal capacity [kJ.g-1.K-1]
The model of Hopkins and Quintiere (1996) for tig:
CF fraction & temperature
tig & critical heat flux Fire resistance of composite
t = 0 s is the exposition to external heat flux
Heat flux
[kW.m-2]56 vol%
CF59 vol%
CF56 vol%
CF59 vol%
CF
14 - 1515 - 1417 - 1413 - 2118 830 1089 22 -20 750 659 26 2430 390 238 30 2540 152 150 32 2850 94 64 33 3060 51 40 36 3375 40 32 35 36
Ignition time, tig [s]
Mass loss [%]
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 7Public
Thermal parameters
TRP: Thermal response parameter characterizes the material resistance to generate a gas combustible mixtureP: Thermal inertia is a measurement of a material ability to resist to a temperature variation
Allows calculation of TRP & P
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 8Public
In-depth temperature
Summary of the thermal parameters
The ignition temperatures of samples are between 240 °C and 300 °C
56 vol% 59 vol%
CHF Tig TRP P
[kW.m-2] [°C] [kW.s1/2.m-2] [kW2.s.m-4.K-2]56 vol% CF 18 240 435 5.07 This work59 vol% CF 14 300 370 2.25 This work
Nylon 14 380 275 0.87 Hopkins, 1996Polyethylene (PE) 9 200 310 1.80 Hopkins, 1996
Polypropylene (PP) 5 210 227 2.20 Hopkins, 1996PMMA 4 180 198 2.10 Hopkins, 1996
Epoxy resin - - 457 - Scudamore, 1991
Material Reference
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 9Public
Mass loss and mass loss rate
Heat flux Ignition time Mass loss
56 vol% 59 vol%
59 vol%56 vol%
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 10Public
1) Resin devolatilization
2) Resin decomposition and production of liquid residue
3) Acceleration of the decomposition rate & combustion of the liquid residue
4) Char pyrolysis and oxidization
The four stages are:
Heat flux = 50 kW.m-2
Decomposition stages
The thermal decomposition of the epoxy resin / carbon fiber composite takes place in four stages
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 11Public
Stage 1Stage 2
Stage 3
Stage 4
Sample combustion in cone calorimeter
Heat flux = 50 kW.m-2
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 12Public
Mass loss rate MLR
The increase of carbon fiber fraction leads to the MLR peak amplitude decrease at a given external heat flux
Heat flux MLR peak width
MLR amplitude Thermal resistance
In accordance to the observations of Pilling et al.
56 vol% 59 vol%
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 13Public
Heat of gasification
Where: L: Heat of gasification [kJ.g-1]
qfl: Heat flux of the flame [kW.m-2]m: Specific MLR (SMLR) [g.s-1.m-2]
Tig, T: Ignition and ambient Temp. [K]: Emissivity [-]σ: Stefan-Boltzmann constant [W.m-2.K-4]
Tv: Vaporisation temperature [K]
TRP L
[kW.s1/2.m-2] [kJ.g-1]56 vol% CF 435 48 This work59 vol% CF 370 44 This work
Nylon 275 3.80 Hopkins, 1996Polyethylene (PE) 310 3.60 Hopkins, 1996
Polypropylene (PP) 227 3.10 Hopkins, 1996PMMA 198 2.80 Hopkins, 1996
Material Reference
CF vol% TRP (volatile production resist)
L (energy to produce volatiles)
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 14Public
ConclusionThe influence of the carbon fiber volume fraction on fire behavior of two epoxy resin (56 and 59 vol% CF) composites was assessed:
The increase of the carbon fiber fraction in the composites leads to a lower thermal resistance of the materialIt was found that all the parameters that characterize the material thermal resistance such as piloted ignition time, thermal response parameter, heat of gasification, thermal inertia and critical heat flux for ignition, decrease when the carbon fiber volume fraction increases from 56 to 59 vol%The thermal decomposition of the composite occurs in four stages: devolatilisation, solid to liquid transition, combustion of liquid residue and char formation
The choice of an optimal carbon fiber fraction is critical to maintain simultaneously good mechanical and thermal resistance properties for epoxy resin/carbon fiber composites
S. Ruban – ICHS2011, Paper No. 182, Sept. 14th 2011 15Public
Acknowledgements
To OSEO for the funding for this projectTo all the team of the Pprime Institute for the laboratory work and their scientific support
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