Modelling the damage to
carbon fibre composites
due to a lightning strike
R. D. Chippendale, I. O. Golosnoy, P. L. Lewin, G.S. Murugan, J Lambert
University of Southampton, UK
19th January 2011
What are Carbon Fibre Composites
• Multi layers of long carbon fibres which have been impregnated into a
polymer matrix
• In each layer the fibre direction is pointing along different orientations
Illustration of few layers of CFC [1]
[1] Composite material revolutionise aerospace engineering, Ingenia, 2008, http://www.ingenia.org.uk/ingenia/issues/issue36/edwards.pdf
Purpose of this Study
•
Growing interesting in using Carbon Fibre
Composite (CFC) as a high tech construction
material. Examples: Wind turbines & Aircraft,
•
This is due to CFC having:
a)
– High strength
– Low weight
•
Problem: Unlike traditional building materials
(aluminium), CFC are highly anisotropic and are
poor electrical and thermal conductors
•
Aim: Optimise the CFC Layout to reduce the
damage caused. This will be done by building a
numerical model to investigate the physical
processes which result from a lightning strike
impacting CFC
[2] Feraboli, P. and M. Miller, Damage resistance and tolerance of carbon/epoxy composite coupons subjected to
simulated lightning strike. Composites Part A: Applied Science and Manufacturing, 2009. 40 (6-7): p. 954 - 967
[3] Uhlig, F., Contribution `a l’´etude des effets directs du foudroiement sur les mat´eriaux structuraux constituant
un a´eronef. 1998, Universit´e de Paris.
b)
Images show the typical damage from
a lightning strike to a) Carbon Fibre
Composite [2] and b) Aluminium [3]
Physical Processes –
Overview
Main Physical Components
•
Initial Carbon fibre composite
material
CFC Cross
section
Main Physical Components
•
Initial Carbon fibre composite material
•
Two inputs into the system:
Plasma channel
– Heat flux from the plasma
channel
– Injection of current into the
material
Injected Current
Main Physical Components
•
Initial Carbon fibre composite material
•
Two inputs into the system:
– Heat flux from the plasma channel
– Injection of current into the material
•
Temperature profile in the material
due to volumetric Joule heating
and the plasma heat flux
Temperature profile
Main Physical Components
•
Initial Carbon fibre composite material
•
Two inputs into the system:
– Heat flux from the plasma channel
– Injection of current into the material
•
Temperature profile in the material due to
volumetric Joule heating and the plasma heat
flux
•
Thermal-chemical degradation
(polymer pyrolysis or phase
change)
•
Due to degradation need to
consider the change in internal
energy and change in materials
Change in material
Main Physical Components
•
Initial Carbon fibre composite material
•
Two inputs into the system:
– Heat flux from the plasma channel
– Injection of current into the material
•
Temperature profile in the material due to
volumetric Joule heating and the plasma heat
flux
•
Thermal-chemical degradation (polymer
pyrolysis or phase change)
•
Due to degradation need to consider the
change in internal energy and change in
materials
•
Gas transport inside material inc.
conservation of energy and mass
•
As hot gas escapes from the
degradation site – change in
internal energy
Gas transport
Numerical Model
•
Built a numerical model to replicate of physical process which occur in a CFC
due to a lightning strike
•
The numerical model is based on an FEA approach
•
Main assumptions of our model:
– Can assume CFC material to be a homogenous anisotropic material
– Only considering the polymer pyrolysis degradation process (Previous
work has shown this to be dominate degradation process) [4]
– Once gas is produced (due to pyrolysis) it immediately escapes. Therefore
we do not consider the gas transport process
– All material properties are assumed constant with temperature
– Material properties are taken for a typical CFC after a literature review
[4] Chippendale, R. D. et. al. MODEL OF STRUCTURAL DAMAGE TO CARBON FIBRE COMPOSITES DUE TO THERMO-ELECTRIC EFFECTS OF
LIGHTNING STRIKES, Proc. 30th International Conference on Lightning Protection
Model Verification
Numerical Model Verification – Experiment?
• Experimental verification was conducted by decoupling the thermal
physical process from the electrical process by using a laser with a well
controlled power input
• Damaged sample was then investigated using X-ray Tomography From these scans the spatial extent of the damage can be determine
• Previous simulations have shown that the majority of volumetric Joule
heating occurs in top few CFC layers. Therefore the joule heating from
a lightning strike can be roughly approximated to surface heating
Experimental Set-up
• Experiment was set up as shown below
• A 6W laser beam operating in 00 mode
• Laser beam had 2mm beam diameter
• Laser beam radiated the CFC for 180 s continuously
• A power density of the chosen laser beam has approximately to be
comparable to that of a lightning strike – however the total power input
is different
CFC
CFC
2mm
Laser beam
source
Laser beam
Side view
Top view of sample
7mm
Results
Experimental Results
•
Cross section X-ray tomography image shown: black is no CFC material, grey is
CFC material
•
Gas was visible given off during first 30 seconds and then stopped being visibly
produced
•
Very localised damage
– No damage visible on sides CFC
– Most of the damage is limited to the top two layers
•
Carbon fibre evaporation is noticed
4.2 mm
0.5 mm
Comparison
•
Similar shape in damage in damage
•
Reasonable agreement between the spatial extent of the damage
Experimental Results
Numerical Model
8 mm
4.6 mm
0.6
7 mm
6.37 mm
Top
down
Volume fraction of
polymer (φ)
Z
X
0 mm
2.25 mm
Cross
section
7.4 mm
2 mm
X
0 mm
10 mm
4 mm
4.2 mm
0.5 mm
0.5 mm
Y
0.3
0 mm
5 mm
0 mm
10 mm
0
Conclusion
Conclusion
• Damage predicted by numerical model agrees fairly
accurately with the experimental results
• Possible reasons for inaccuracies:
– No exact material properties are known (thermal
conductivity, pyrolysis energies)
– No gas transport included
• Next steps: Inclusion of gas transport
Main Physical Components
Plasma surface
heating around
attachment area
Lightning strike
current Profile
Electrical conduction
resulting in
volumetric joule
heating
Variation in
bulk material
properties
Temperature profile
inside material
Thermo-Chemical
degradation (phase
change & pyrolysis)
Gas transport in
material inc.
Conservation of
energy and mass
Thermo-mechanical
response – differential
thermal expansion,
delamination of CFC
ply and internal cracks
(not included here)