1. Modelling the damage to carbon fibre composites due to a lightning strike
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R. D. Chippendale, I. O. Golosnoy, P. L. Lewin, G.S. Murugan, J Lambert
University of Southampton, UK 19th January 2011

2. 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
The reason for considering anistropic materials is the focus of my research is regarding CFC Carbon fibre composites are made from long highly conductive carbon fibres, which are encapsulated in poorly conductive polymer. As a result CFC are highly anisotrpoic
CFC are constructed from several layers (as shown) and so the conducive nature of CFC is complex
As a result of our models we notice highly unexpect results
Illustration of few layers of CFC [1]
[1] Composite material revolutionise aerospace engineering, Ingenia, 2008,

3. Purpose of this Study a) b)
Growing interesting in using Carbon Fibre Composite (CFC) as a high tech construction material. Examples: Wind turbines & Aircraft,
This is due to CFC having:
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 a) b)
Images show the typical damage from a lightning strike to a) Carbon Fibre Composite [2] and b) Aluminium [3]
[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, (6-7): p
[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.

4. Physical Processes – Overview

5. Main Physical Components
Initial Carbon fibre composite material
CFC Cross section

6. 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
Plasma channel
Injected Current

7. 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

8. 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

9. 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

10. 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

11. Model Verification

12. 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

13. 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
7mm
Laser beam source
Laser beam
Side view
Top view of sample

14. Results
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15. 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

16. Volume fraction of polymer (φ)
Comparison
Similar shape in damage in damage
Reasonable agreement between the spatial extent of the damage
Experimental Results
Numerical Model
Volume fraction of polymer (φ)
8 mm
0.6
4.6 mm
7 mm
Top down
6.37 mm Z X
0 mm
7.4 mm
0.3
0 mm
10 mm
2 mm
4 mm
2.25 mm
Cross section
4.2 mm
0.5 mm Y
0.5 mm
0 mm X
0 mm
5 mm
10 mm

17. Conclusion
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18. 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

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20. Main Physical Components
Temperature profile inside material
Electrical conduction resulting in volumetric joule heating
Lightning strike current Profile
Plasma surface heating around attachment area
Variation in bulk material properties
Thermo-Chemical degradation (phase change & pyrolysis)
Thermo-mechanical response – differential thermal expansion, delamination of CFC ply and internal cracks (not included here)
Gas transport in material inc. Conservation of energy and mass
Thermo-chem reduce temp due to endothermic and thermal transport due to different c, den , K
Gas transport changes temp
Variation in material properties, due to reaction and sublimation effects
Change in properties effects tharmal expansion
Gas causses intertnal stress, further stress strain due to expansion
Variation of properties effects joule heating