Lightning-Induced Ablation CFRP Composites

Surface Ablation in Fiber-Reinforced Composite
Laminates Subjected to Continuing Lightning Current
Yeqing Wang
Advisor: Dr. Olesya Zhupanska
Mechanical Engineering Department
The University of Iowa
01/05/2016
57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference,
4-8 Jan, 2016, San Diego, CA.

 Introduction
 Problem description
 Development of physics-based model describing electrical and thermal
interaction between the lightning channel and composite structure
1. Characterization of lightning arcs (current density, heat flux)
2. Temperature-dependent density, electrical, and thermal properties of
CFRP composite
3. Modeling of lightning-induced ablation in composite structure
 Case study
1. NASA carbon fiber polymer matrix composite panel
 Conclusion
Outline

Composite Materials for Aerospace Industry
 Composite materials on B787
Glass fiber
composite fabric
Carbon fiber
composite fabric
B787 Materials [1]
[1] http://aviationknowledge.wikidot.com/aviation:boeing-787-advancements

Motivation
 One strike is expected during every 3000 flight hours for a typical commercial
aircraft, or approximately one strike per year per plane [2]
 Fiber reinforced polymer matrix composites are vulnerable to lightning strikes
[2] Rakov, V. A., and Uman, M. A., Lightning: Physics and Effects. Cambridge University Press, 2007.
[3] http://www.telegraph.co.uk/news/aviation/11814112/Lightning-strikes-Boeing-737-plane-preparing-for-take-off.html
[4] https://www.quora.com/What-happens-if-lightning-strikes-a-plane
The moment direct lightning strikes a Delta Airlines
plane about to take off in Atlanta [3]
8:47AM BST 21 Aug 2015
https://youtu.be/HZVX921Z0wc
[4]

Direct Effects of Lightning Strike on Composites
 Rapid temperature rise, melting or burning at the lightning attachment points
 Mechanical damage due to magnetic force and acoustic shock wave
Lightning
Current
Injection:
High-intensity
Short-duration
Rapid
temperature
rise
Resin starts to
decompose:
~330 °C
Fully
decomposed:
~800 °C
Fiber rapid
sublimation:
Ablation

How Does Lightning Strike Form?
1. Lightning stepped leader (weakly luminous) travels through the air towards
the ground structure
2. Ground structure emits answering leader to meet lightning stepped leader
3. Once they are connected, the first luminous return stroke forms
Lightning
stepped leader
Answering
leader
First return
stroke

Objectives
1. Develop a physics-based model describing electrical and thermal
interaction between the lightning channel and the composite structures
2. Develop computational procedures for predicting lightning-induced
ablation damage in composite structure
3. Perform case study:
1. NASA Carbon Fiber Reinforce Polymer Matrix (CFRP) composite panel
Lightning channel
Joule heating
CFRP composite panel
Conduction heat flux

Problem Description
1. Characterization of lightning arcs
(current density, heat flux)
• Lightning arc radius expansion
• Conduction heat flux
• Joule heating
2. Temperature-dependent material
properties of CFRP composites
• Density
• Electrical and thermal conductivities
3. Heat transfer problem formulation
• Highly nonlinear
• Moving boundary conditions
Lightning
channel
Joule heating
CFRP composite
panel
Conduction
heat flux

Outline
 Introduction
2. Temperature-dependent density, electrical, and thermal properties of CFRP
composite
 Case study
 Conclusion

Lightning Channel Radius Expansion
 Lightning channel expansion during initial discharge stage:
h
a
bz
rO
R(t)
Q(r, t)
Lightning Current
Injected Heat Flux
1/3 1/2
( ) 0.097 , 50 μspeakR t I t t 
<Lightning channel radius expansion>
[5] Braginskii, S. I. (1958).. SOVIET PHYSICS JETP-USSR, 7(6), 1068-1074. [6] Plooster, M. N. (1971). Physics of Fluids (1958-1988), 14(10), 2124-2133.
[7] Paxton, A. H., Gardner, R. L., & Baker, L. (1986). Physics of Fluids (1958-1988), 29(8), 2736-2741. [8] Hill, R. D. (1990). Physics of Fluids B: Plasma
Physics (1989-1993), 2(12), 3209-3211.
1/3 1/2
( ) 0.28 ( ) , 50 μsR t I t t t 
<Standard lightning current waveform>

Lightning Current Density
 Experimental measurements indicate that electric arc current density J(r) has a
non-uniform Gaussian-like spatial profile:
2
max ( )( , ) , ( ).cr
J r t e rJ t R t
 
• c is determined by fitting
experimental data
• Jmax is determined by the
relationship: the integral of current
density equals to the total current
<Current density profile on composite surface>
[9] Nestor, O. H. (1962). Journal of applied physics, 33(5), 1638-1648. [10] Tsai, N. S., & Eagar, T. W. (1985) Metallurgical Transactions B, 16(4), 841-846.
[11] Lowke, J. J., & Tanaka, M. (2006). Journal of Physics D: Applied Physics, 39(16), 3634. [12] Chemartin, L., Lalande, P., Delalondre, C., Cheron, B., & Lago,
F. (2011). Journal of Physics D: Applied Physics, 44(19), 194003.
0
1
2
3
4
5
6
7
0 0.002 0.004 0.006 0.008 0.01
CurrentDensity(·106A/m2)
Radial Distance (m)
Nestor, 1962
Tsai & Eagar, 1985
Lowke & Tanaka, 2006
Chemartin, et al., 2011
Our Model
I=200 A
R=10 mm
 2
( )
( )
( , ) , ( ).
1 cR t
c I t
J r t r R t
e 

 


Lightning-Current-Induced Conduction Heat Flux
 Lighting-current Induced heat flux (Q) is approximately linear to the lightning
current density (J):
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.002 0.004 0.006 0.008 0.01
TotalHeatFlux(107·W/m2)
Radial Distance (m)
Tanaka et al., 2002
Nestor, 1962
Tsai & Eagar, 1985
Lowke & Tanaka, 2006
Our Model
I=150 A
R=10 mm
0
2
4
6
8
10
12
14
0 0.002 0.004 0.006 0.008 0.01
TotalHeatFlux(107·W/m2)
Radial Distance (m)
Nestor, 1962
Lowke et al., 2007
Gonzalez et al., 2005
Lago et al., 2004
Our Model
I=200 A
R=10 mm
<Amplitude of heat flux due to lightning on the composite material surface>
[9] Nestor, O. H. (1962). Journal of applied physics, 33(5), 1638-1648. [10] Tsai, N. S., & Eagar, T. W. (1985) Metallurgical Transactions B, 16(4), 841-846.
[11] Lowke, J. J., & Tanaka, M. (2006). Journal of Physics D: Applied Physics, 39(16), 3634. [13] Tanaka, M., Terasaki, H., & Ushio, M. (2002). ISIJ international,
42(9), 1005-1009. [14] Lago, F., Gonzalez, J. J., Freton, P., & Gleizes, A. (2004). Journal of Physics D: Applied Physics, 37(6), 883.
 
5
10
2
b
a mat arc anode
k
Q J U T T J

 
      
 

Outline
 Introduction
2. Temperature-dependent density, electrical, and thermal properties of
CFRP composite
 Case study
 Conclusion

Why Material Properties are Temperature Dependent?
 Resin decomposition
 Thermal oxidation (e.g., C+O2 = CO2), for carbon fiber composites
 Fiber phase transition:
• Sublimation temperature: CFRP: ~3316 °C
Lightning-
induced heat
flux:
High-intensity
Short-duration
Rapid
temperature
rise
Resin starts to
decompose:
~330 °C
Fully
decomposed:
~800 °C
Fiber rapid
sublimation:
Ablation
Mass loss and Temperature-dependent electric, thermal and
physical properties

0
10
20
30
40
50
60
70
80
90
100
0 500 1000 1500 2000 2500 3000 3500
ElectricalConductivity(S/mm)
Temperature (°C)
Resin starts to
decompose
Carbon
sublimation point
Temperature Dependent Material Properties for CFRP Composites
 NASA CFRP composite substrate
• Unidirectional Hexcel 8552/AS4 composite lamina
• Woven fabric Hexcel 8552/AS4 composite lamina
Electrical Conductivity
(1/Ω·m)
Carbon fiber AS4 5.88·104
Hexcel 8552 resin 4.9·10-16
 Temperature-dependent
• Anisotropic electrical conductivity
• Anisotropic thermal conductivity
• Specific heat
• Density
<Electrical conductivity in fiber direction>
 Effect of carbon oxidation is not
considered

Lightning-Current-Induced Electric-Thermal Coupling
h
a
bz
rO
R(t)
Q(r, t)
Lightning Current
Injected Heat Flux
 Governing equations:
 ( ) ( ) J
T
T T C T Q
t


    

k
0
( ) ( , )z
z
T
k T Q r t
z 

 

 4 4
0
( )z
z
T
k T T T
z
 


  

0
( ) ( , )z
z
T J r t
z




 

0  J Maxwell's equation of
conservation of charge
 Boundary conditions:
 Coupling arises from:
JQ  J E
JQ  J E
( )T
1. Source 1:
2. Source 2:

Moving Boundary Conditions
 Moving boundary conditions come from:
1. Lightning channel expansion (during initial stage of lightning discharge)
2. Material instant removal due to fiber sublimation
• When temperature exceeds sublimation temperature, material will be
instantly removed (i.e., ablation takes places)
Current Density and Heat flux boundaries needs to be
updated during the computational procedure

Tracking Moving Boundaries in FEM: Existing Tool
 Method 1: Abaqus subroutine Umeshmotion+ALE:
• Can handle moving boundary, but cannot handle multiple material domains
Receding surface, T=Tabl
N1 N2
N3N4
x
y
yabl
N1’ N2’
(a)
ξ
η
(-1,-1) (1,-1)
(-1,1) (1,1)
ηabl
N1 N2
N4 N3
N1’ N2’
(b)
Heat Flux
Heat Flux
T=sublimation
temperature
T>sublimation
temperature
T<sublimation
temperature
<physical coordinate> <normalized coordinate>

 Method 1: Abaqus subroutine Umeshmotion+ALE:
• Can handle moving boundary
• Cannot handle multiple material domains
• Cannot be used in electric-thermal coupled analysis
Material 1
Material 2
Interface
Ply 1
Ply 2
Interface
Tracking Moving Boundaries in FEM: Existing Tool Limitation

 Method 2: Element Deletion Method:
• Can handle moving boundary and multiple material domains
• Can be used in electric-thermal coupled analysis
Receding surface, T=Tabl
Volume of material needs to be removed theoretically
Element numerically removed by ABAQUS
N1 N2
N3N6
yabl
Heat Flux
N4N5
t=t1
(a)
1, 2
1
N N
t ablT T
ablT
3, 6
1
N N
t ablT T
1
2
(b)
N1 N2
N3N6
yabl
N4N5
2 1
1, 2 1, 2N N N N
t t ablT T T 
ablT
2
3, 6N N
t ablT T
t=t2 (t2>t1)
1
2
(c)
N3N6
yabl
N4N5
2
3, 6N N
t ablT T
t=t2 (t2>t1)
2
(a) t = t1 (b) t = t2 > t1
Tracking Moving Boundaries in FEM: Newly Developed Tool
<Element deletion method>

Start FEA Analysis
in ABAQUS
Identify the
element IDs
Remove these
elements
Calculate the
new boundary to
apply heat flux
Time
Increment i
Read temperature at bottom
nodes of each element after
time increment i
Temperature
> Tabl
i=1
i = final
increment ?
End
i=i+1
Restart the analysis
at increment i
i=i+1
Yes
No
YesNo
Matlab-Abaqus Integrated
Computational Procedure
Element Deletion Method Implementation in FEM

Case Study: NASA Carbon Fiber Composite Panels
 Consists of 16 unidirectional Hexcel 8552/AS4 composite lamina layers and 2
woven fabric Hexcel 8552/AS4 composite lamina layers
 Laminate schedule: [(0/90F)/45/90/-45/0/45/90/-45/0/0/-45/90/45/0/-
45/90/45/(0/90F)]
 Total thickness: 2.47 mm
h
a
bz
rO
R(t)
Q(r, t)
Lightning Current
Injected Heat Flux
CFRP composite
panel
<NASA CFRP panel installed in test bed>
Laboratory
artificial spark
generator
CFRP Panel

Case Study: Lightning Current Applied
 Lightning channel radius during component C
• Experimental test (laboratory artificially generated electric spark): Not
mentioned
• Computational study: 18.87 mm (calculated using our model)
<Lightning current waveform used in NASA
tested >
 Ablation due to the lightning current
component D is not considered (extreme
short and insignificant ablation)
 Only the ablation due to the lightning current
component C is predicted
1/3 1/2
( ) 0.097 , 50 μspeakR t I t t 
Time
(not to scale)
Current
(not to scale)
D B C*
Current Component
Waveforms
Component Component D Component B Component C
Specifications
kA ×106 A2·s
Not Applied
A ms Coulombs
20.8 0.220 368 468 172

Computational Result: Ablation Profile
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0 0.1 0.2 0.3 0.4 0.5
DepthofAblation(·10-3m)
Time (s)
Layer 1, [(0/90F)]
Layer 2, [45]
Layer 3, [90]
Layer 4, [-45]
Layer 5, [0]
Layer 6, [45]
Layer 7, [90]
Layer 8, [-45]
Layer 9, [0]
 Maximum ablation depth in the center:
1.02 mm
 Radius of the ablation area is: 13 mm
 Approximately 7 laminate layers are
completely consumed
<Ablation depth vs. time> <Ablation zone profile>
Thickness:
1.75 mm ~12 mm
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
-20 -10 0 10 20
DepthofAblation(·10-3m)
Position in the x Direction (·10-3 m)
t = 0.468 s
t = 0.300 s
t = 0.150 s
Layer 1,
[(0/90F)]
Layer 2, [45]
Layer 3, [90]
Layer 4, [-45]
Layer 5, [0]
Layer 6, [45]
Layer 7, [90]
Layer 8, [-45]
Layer 9, [0]
13 mm

Computational Result: Ablation Profile
z
x
y
o
t = 0.150 s
t = 0.468 s

NASA Experimental Result: Ablation Profile
<Ultrasonic C-scan damage> <Ablation profile by Pulse Echo Unit>
 Maximum ablation depth in the center: 1.016 mm
• Computational result: 1.020 mm (Match well)
 Radius of the ablation area is: 23 mm
• Computational result: 13 mm
• Mismatch between the predicted lightning channel radius used in FEA
simulation and the laboratory generated artificial lightning spark channel
radius in the experimental tests

Conclusion
1. Developed a physics-based model describing electric, thermal interaction
between the lightning channel and CFRP composite panel
• Most advanced model related to lightning strike damage in composite
structure in existing literature
2. Applied the developed models for evaluation of material ablation in the
NASA carbon fiber-reinforce polymer-matrix composite substrate due to
simulated lightning current injection

Acknowledgements
The authors would like to acknowledge the support from the National Science
Foundation under Grant Number EPS-1101284. Any opinions, findings,
conclusions or recommendations expressed in this work are those of the author
and do not necessarily reflect the views of the National Science Foundation.
The authors thank Drs. Brett A. Bednarcyk, Evan Pineda, and Paria Naghipour
(NASA Glenn) for pointing out to the experimental study and for many helpful
discussions.
Yeqing Wang also thanks the Air Force Research Lab (AFRL) Mathematical
Modeling and Optimization Institute and Dr. Crystal Pasiliao (AFRL) for the
support of this research during Summer 2015.

Thanks for Attention!
Questions?

Lightning-Induced Ablation CFRP Composites

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