Factors affecting direct lightning strike damage to fiber reinforced composites: A review

Journal Pre-proof Factors affecting direct lightning strike damage to fiber reinforced composites: A review Vipin Kumar, Tomohiro Yokozeki, Christian Karch, Ahmed A. Hassen, Christopher J. Hershey, Seokpum Kim, John M. Lindahl, Abigail Barnes, Yashwanth K. Bandari, Vlastimil Kunc PII:

S1359-8368(19)32249-8

DOI:

https://doi.org/10.1016/j.compositesb.2019.107688

Reference:

JCOMB 107688

To appear in:

Composites Part B

Received Date: 19 May 2019 Revised Date:

4 October 2019

Accepted Date: 4 December 2019

Please cite this article as: Kumar V, Yokozeki T, Karch C, Hassen AA, Hershey CJ, Kim S, Lindahl JM, Barnes A, Bandari YK, Kunc V, Factors affecting direct lightning strike damage to fiber reinforced composites: A review, Composites Part B (2020), doi: https://doi.org/10.1016/ j.compositesb.2019.107688. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Factors Affecting Direct Lightning Strike Damage to Fiber

1

Reinforced Composites: A Review

2

Vipin Kumar1*, Tomohiro Yokozeki2, Christian Karch3, Ahmed A. Hassen1, Christopher J.

3 4

Hershey1, Seokpum Kim1, John M. Lindahl1, Abigail Barnes1, Yashwanth K. Bandari1, Vlastimil

5

Kunc1

6 7

1

Material Science and Technology Division, Manufacturing Demonstration Facility (MDF), Oak Ridge National Laboratory (ORNL), Knoxville, TN 37932, USA

8 2

9

Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan

10 3

11

Airbus Defence and Space GmbH, Manching, 85077 Germany *[email protected]

12 13 14

Abstract:

15

In recent years, Carbon Fiber Reinforced Plastics (CFRP) or Glass Fiber Reinforced Plastics

16

(GFRPs) have become a very common material for aircraft and wind turbine structures. These

17

structures are often protected from lightning strikes using conventional metal-based protective This manuscript has been authored by UT-BATTELLE, LLC under contract no. De-AC05-00OR22725 with the U.S. Department of Energy. The United States government retains and the publisher, by accepting the article for publication, acknowledges that the United States government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States government purposes. The department of energy will provide public access to these results of federally sponsored research in accordance with the DOE public access plan (http://energy.gov/downloads/doe-public-accessplan).

1

films/foils. Non-conventional, non-metallic lightning strike protection (LSP) technologies have

2

not yet been fully realized, but research on non-conventional LSP systems for CFRPs has gained

3

momentum in the last few years. The discovery of new structural conductive materials and

4

improvements in the processing of carbon nano-filler based composites have challenged the

5

conventional metal-based LSP systems by providing the potential for lightweight, non-metallic

6

alternatives. However, a major challenge in using non-conventional LSP is the complex nature of

7

a lightning strike event and its complicated thermal and mechanical impact on CFRP structures.

8

Understanding the direct effect of a lightning strike on a CFRP structure requires understanding

9

multiple transient loads, such as electrical, thermal, magnetic, acoustics, shock, and inertia. This

10

review article focuses on new findings and discusses the complex direct effects of lightning on

11

CFRPs. The focus is to find the important factors that regulate and control the damage to FRPs

12

are classified and discussed with the help of available literature based on experimental results.

13

Possibilities and limitations to these new findings are also discussed.

14 15

Keywords: Polyaniline, CFRP, Adhesive, Lightning Strike Protection, Multifunctional Composites.

16

Abbreviations:

17

CFRP, Carbon Fiber Reinforced Plastic; LSP, Lightning Strike Protection; FRP, Fiber

18

Reinforced Plastics/Polymer; EMF, Expanded Metal Foil; CNT, Carbon Nanotube; RGO,

19

Reduced Graphene Oxide; CNF, Carbon Nanofiber; SWCNT, Single Wall Carbon Nanotubes;

20

MWCNT, Multi-Wall Carbon Nanotubes; BP, BuckyPaper; PCFP, Pitch-Based Carbon Fiber

21

Paper; PANI, polyaniline; DBSA, Dodecylebenzenesulfonic Acid; Ag, Argentum (Silver); C,

22

Carbon; P, Phosphorus; Sn, Stannum (Tin); CF, Carbon Fiber; NCF, Non-Crimp Fabric; BMI,

2

1

Bismaleimide;

PEEK,

Polyetheretherketone;

2

Aeronautics and Space Administration

DVB,

Divinylbenzene;

NASA,

National

3

4

1.

Introduction

5

Metal-based structures are becoming less prevalent in the modern advanced aircraft.

6

Manufactures are seeking lightweight alternative structures, such as Carbon/Glass fiber

7

reinforced plastic (CFRP/GFRP) composites, to replace them [1]. Fiber reinforced composites

8

have revolutionized industries in which the primary focus is on weight reduction and design

9

improvements. Examples include the aerospace, energy, sports, marine, and automobile

10

industries [2,3]. While CFRPs have addressed issues regarding weight reduction, high specific

11

stiffness or strength, tunable mechanical properties, and corrosion resistance, etc., they still face

12

significant challenges related to the material, manufacturing, maintenance and repair costs [4].

13

The traditional metal frames of aircrafts, due to their high electrical conductivity, were highly

14

effective in dissipating lightning strike currents and suppressing their direct effects, although

15

there was still a concern regarding indirect effects and the induced effect of lightning strikes on

16

fuel tanks and electronics [5–7]. However, these traditional metal frames are being replaced

17

mainly by advanced CFRP composites in modern aircrafts. A less frequently discussed property

18

of CFRPs is their low and anisotropic electrical conductivity which can be an advantage or

19

disadvantage depending on its application [8]. The low electrical conductivity of CFRP can be a

20

considerable disadvantage in the event of a lightning strike on CFRP structures [7,9–11]. A

21

lightning strike on aircraft might not seem common, but reports show that there are

22

approximately 216 million flash counts (any kind of lightning) during a decade time (1989-98) in

23

the USA alone [12] and, on an average, every aircraft gets struck by at least one lightning strike 3

1

at some point during its 2000-5000 hour lifetime. The Tampa-Orlando-Cape corridor across

2

Florida is known as the lightning capital, with a flash density of nine flashes per km2. When in

3

areas with a high flash density such as this corridor, aircrafts and windmill farms are at an

4

especially high risk of impact from a lightning strike [13–17]. If these structures are composed of

5

CFRPs, they require additional lightning strike protection systems due to the vulnerability of

6

CFRPs to damage from lightning strikes [18].

7

The current LSP systems mainly consist of metal-based material, which are associated with

8

issues such as parasitic weight, integration cost, debonding with CFRP substrate and a very high

9

repair cost. The most advanced commercially available lightning strike protection products are

10

shown in Table 1. Another emerging issue with current LSP system is their non-compatibility

11

with thermoplastic composites (thermoplastic composites are being researched extensively to

12

replace thermosetting composites in future aircraft). From this literature review, it is confirmed

13

that a few research areas still require comprehensive studies, such as effect of carbon fiber type,

14

effect of sizing on electrical conductivity and thermal stability of carbon fiber weave-patterned

15

hybrid layups (combination of conductive layers and insulating layers). With the introduction of

16

new LSP materials, their integration method and cost are also worth investigation.

17 18

Table 1. Most advanced commercially available lightning strike protection products. LSP Type

Supplier

Product

Metallic Mesh/foil

1

Dexmet Corp. (now PPG)

MicroGrid®

(Al,Cu)

2

Astroseal Products Mfg. Corp.

Aerostrike

3

The Gill Corporation-Maryland

PAA-CORE®, Strikegrid®

1

Cytec Engineered Materials

SURFACE MASTER

Hybrid LSP (Mesh +

4

adhesives)

2

Hexcel

Hexply, IWWF fabric

3

Henkel

LOCTITE® EA 9845 LC AERO, SynSkin

4

3M

3MTM Scotch-WeldTM AF536

5

Toray

Toray TC235SF surfacing films Toray Cetex® RTL

Metalized fibers for

1

Hollingsworth & Vose Co.

Surfacing Veils

LSP (Ni/Cu coating

2

Conductive Composites

Ni-Shield

on CF)

3

Veelo Tech.

VeeloVEILTM

4

Technical Fiber Products Inc.

20444A/B

1

LORD Corporation

UltraConductive

Conductive surfacing film 1 2

A 2013 review by Gagne et al. covered a wide range of LSP technologies which were being

3

used or could be used in the future [19]. They reviewed the lightning phenomenon, LSP

4

principles, electromagnetic shielding, government regulations, and industry standard. Gagne et al.

5

presented detailed literature about current technologies and potential candidates for lightning

6

protection in the future. Another very informative review article by Karch et al. reviewed the

7

traditional metal-based LSPs, lightning current waveforms, zoning of aircraft according to

8

lightning strike probability, and discussed nano-composite LSP technologies [20]. Both reviews

9

by Gagne et al. and Karch et al. provide an excellent starting point regarding current status of the

10

LSP technology. However, neither review covers the full scope of the current research on LSP of

5

1

CFRPs. In the last five years, there has been a surge in research resulting in more than 150

2

articles published on the experimental and numerical aspects of LSP of CFRPs. Numerical

3

simulation of such a complex phenomenon itself is a huge challenge, which requires a lot of

4

assumptions [21–26]. The direct effect of lightning strike on CFRPs is difficult to simulate

5

accurately by numerical methods [27–31]. Researchers have reported persuasive numerical

6

modeling, which will not be addressed in this paper. This review paper focuses on new

7

technologies which are experimentally tested and reported. Factors affecting direct damage to

8

CFRPs is are the main topics of interest, and non-metal based LSP techniques are given special

9

attention as well. Advantages and disadvantages of new findings are presented and discussed.

10

This review also attempts to address some misconceptions in order to assist future research in

11

this area.

12 13

2. The Components of a Lightning Strike

14

Generally, a lightning strike is caused by the high voltage electric breakdown of the air

15

between highly charged storm clouds with high electric strength. An aircraft can trigger these

16

breakdowns, due to enhancement of the electric field strength at the aircraft extremities.

17

Lightning can occur from cloud to cloud, cloud to ground or ground to cloud. Cloud to cloud

18

lightning is a concern for the aerospace industry since aircraft at cruising altitude between highly

19

charged clouds is very susceptible to a lightning strike. However, the major concern is cloud to

20

ground lightning discharge, because of high susceptibility of the aircraft during take-off and

21

landing as well as high current loads at low altitudes [32]. Some basic terminologies, test

22

environment and waveform of lightning strike are defined by the SAE ARP-5412B standard as

23

shown in Figure 1.

6

1 2

Fig. 1 Lightning waveform defined by SAE ARP-5412B [33].

3

The lightning waveform standard is comprised of multiple strokes of different intensities and

4

dwell time. The first component of the defined waveform is high intensity current “Component

5

A”. The return stroke is the bright flash caused by the rapid discharge of lightning current from

6

negatively charged stepped leader to the positively charged ground or streamer. The conductive

7

path left behind by the initial return stroke can be used by remaining charge for a smoother

8

discharge to the ground. According to standard SAE ARP-5412B, Component A is followed by

9

an intermediate intensity current termed as Component B. Components A and B are part of the

10

first return stroke of the lightning strike.

11

Component B is followed by a continuous current stroke termed as Component C. This

12

waveform is associated with what is called the “hang on phenomenon” of current on the surface

13

of an aircraft (from the attachment point in the backward direction due to forward motion of

14

aircraft) and therefore also known as swept stroke. A crucial parameter is the dwell time, which

15

is a function of the aircraft’s speed and the type and thickness of the dielectric coating on the

16

airframe structure. According to European standard for lightning environment and waveform

17

(ED-84), the dwell time of 20 ms is recommended. In European aerospace companies, the upper

18

limit of dwell time of 50 ms is widely used as default as the worst-case scenario for continuing

19

lightning current tests [34,35]. A rough total charge of 28 C, which include contribution of 7

1

current component B (10 C) + contribution of current component C (45 ms × 400 A = 18 C) is

2

transferred during current component during dwell time. This large amount of current is the most

3

important parameter for melting and puncture of metallic structures [36]. The final waveform is

4

component D, which is also known as the re-strike current [37]. Generally, transient component

5

A and D cause the most significant damage to the CFRP structure. Most of the experimental and

6

numerical studies covering Component A induced damage except a few [38].

7

According to ARP5414 standard, the lightning current waveforms which are applied for an

8

assessment of structural damage in a laboratory experiment depends upon the location of the

9

considered airframe part (on the aircraft zoning area) [39] as shown below.

10

Zone 1A

A+B+C* (C* is a reduced C component)

11

Zone 1B

A+B+C+D

12

Zone 1C

Ah+B+C*. The impulse Ah corresponds to a « lower » impulse A.

13

Zone 2A

D+B+C*

14

Zone 2B

D+B+C

15

Zone 3

A+C. The lightning current is applied by conduction.

16

3. Direct Effects of Lightning Strikes on FRPs

17

The probability that lightning might strike an aircraft depends on geographical location,

18

cruising altitude, temperature, and weather during operation. Most lightning strike events on an

19

aircraft are reported during the climb and descent phases of flight [40]. The intensity of lightning

20

current can vary from a few hundred amps to over 200,000 amps. The transient current is

21

transmitted to the CFRP structures during the lightning event over a very short period [40].

22

Chemartin et al. presented a comprehensive study of direct lightning strike effects on FRPs,

23

detailing the lightning arc attachment phenomenon through separate analysis of thermal and 8

1

mechanical loads during lightning strike events [35]. The thermal loading was attributed to the

2

heat generated by the Joule heating effect; the sudden increase in the temperature was due to

3

resistive heating caused by current flowing in a resistive material. Joule’s heating is one of the

4

main factors of the direct damage to the CFRP structures due to lightning strikes. The sudden

5

increase in temperature around the lightning attachment zone can cause melting, sublimation, or

6

evaporation of the matrix material, leading to the generation of hot gases. Entrapment of these

7

hot gases within laminates can create transient mechanical loads due to thermal expansion and

8

contraction, resulting in delamination, puncture, and fiber breakage in the CFRP laminate

9

[9,41,42]. Figure 2 illustrates various direct loads on composite structure at the lightning

10

attachment zone [35]. Karch et al. reported earlier that the contribution of thermal radiation from

11

the hot plasma has a negligible effect on the damage to the substrate structures [43]. His work on

12

mechanical loads and their effect during lightning strikes is important for understanding the

13

complex behavior of lightning strikes [44–47].

14 15

Fig. 2. Illustration of the various direct loads at composite structure at the lightning attachment

16

zone [35]. 9

1

A return stroke of lightning current heats the weak ionized dart leader in a very short time

2

span, which causes a rapid increase of plasma pressure [48,49]. According to Karch et al., this

3

overpressure gives rise to the expansion of the plasma channel and generates a shockwave. He

4

explained that shockwaves produced by lightning discharge can induce significant damages to

5

the structures. In case of lightning strike-protected CFRP, the sublimation and evaporation of the

6

LSP and epoxy resin generates a hemi-spherical shock wave at the upper side of the protected

7

CFRP laminate [50]. Moreover, dielectric coatings like polyurethane paints confine the current

8

flow and enhance the shockwave generated on the underlying CFRP laminates. There is

9

currently very little experimental research conducted to measure the shock loading on the CFRP

10

structure directly due to lightning strikes [51]. Therefore, work by Hirano et al. on the effect of

11

shockwaves and the subsequent initial displacement of substrate CFRP structure is of very high

12

importance. His group utilized a high speed camera to show the generation of different

13

shockwaves with different kinds of discharge probes, as shown in Figure 3 [52]. In this work,

14

they also experimentally studied the material deformation and damage behavior due to a

15

shockwave. A few theoretical, semi-analytical and numerical prediction studies are also available

16

regarding shockwave effects [53,54].

17

10

1

Fig. 3 (a) and (b) shows the result of visualized shockwave propagation with needle electrode and with jest divertor electrode, respectively [52].

2 3

Another crucial mechanical load during lightning attachment is generated by the magnetic

4

forces induced by the tidal high-intensity current, which result in internal arcing between plies or

5

conductive carbon fibers that can lead to damaged CFRP structures. The exact amount of

6

magnetic forces on the substrate structure during a lightning strike has not been broadly explored

7

using experimental methods. A few analytical solutions are available that provide an underlying

8

mechanism of the magnetic forces due to lightning strikes [55]. Karch et al. also applied an

9

analytical approach for current flow distribution and generated magnetic field thereof. They used

10

an analytical approach to derive numerical data for FEM analysis and estimated the mechanical

11

loads during a lightning event [56,57]. The derivation of these forces is outside the scope of this

12

review.

13

The effect of waveform parameters (maximum current, rise time, electric charge and specific

14

energy) can also significantly affect the damage extended to the CFRP structures. The earlier

15

work of Hirano et al. showed how the extent of damage of an unprotected CFRP structure is

16

directly proportional to the applied specific energy (action integral) [58]. Different waveform

17

parameters have also been studied, particularly how they cause different kinds of damage to the

18

structure [59]. Li et al. also discussed how charge transfer, action integral and acoustic shock are

19

directly related to resin pyrolysis, delamination and fiber damage areas respectively [60].

20

4. Factors affecting lightning strike damage to FRPs:

21

4.1 Effect of in-plane and through-thickness electrical conductivity of CFRP

22

The primary cause of catastrophic damage to CFRP structures is either the

23

degradation/evaporation of the resin of the CFRP laminate or the hemi-spherical evaporation of 11

1

the LSP and epoxy at the top of protected CFRP laminates. These effects are mainly fed by the

2

heat generated by the Joule heating from the transient current components of the impressed

3

lightning, and the heat transfer from the hot plasma channel at the arc root. Therefore, most of

4

the work to mitigate the lightning damage to CFRPs is based on improving the surface, in-plane

5

and through-thickness electrical conductivity of different LSP measures of CFRP laminates,

6

using various techniques. The most reported method involves the placement of an electrically

7

conductive coating on top of less-conducting CFRPs or the addition of electrically conductive

8

fillers to increase the electrical conductivity of the composite itself [61,62]. While carbon fibers

9

are electrically conductive, they are embedded in insulative resins, which make the CFRP a less-

10

conducting material than metals like copper or aluminum. An another logical way to improve

11

CFRP conductivity is to embed conductive fillers in a resin to make the resin more electrically

12

conductive. Martin et al. and Karch et al. both summarized formulations of epoxy resins with

13

carbon allotropes in their respective review articles [19,20,63]. They compiled a large number of

14

carbon nanotube and graphene-based literature and discussed their merits and demerits. They

15

summarized that the dispersion and distribution problems associated with nanoparticles need to

16

be addressed to get the best results. In both aforementioned reviews, the authors underlined the

17

challenges related to carbon nanomaterial-based nanocomposite such as low electrical

18

conductivity, feasibility, and reparability cost.

19

4.1.1 Effect of conductive layers and coatings

20

This section evaluates the improved surface conductivity, and its effect on lightning damage,

21

of CFRP panels due to the addition of conductive layers or coatings. Most common metal-based

22

lightning strike protection techniques are primarily designed to enhance the surface electrical

23

conductivity using supplementary materials, for example, expanded metal foils (EMF), metal-

12

1

mesh, conductive strands under laminates, ply-integrated LSP and metalized fabric [41,64–66].

2

Most of the above-mentioned commercial LSP technologies are based on metals. However,

3

recently researchers have reported a few non-metallic LSP techniques as well. LSP based on

4

carbon-based nanomaterials, i.e. carbon nanotube (CNT), graphene, and carbon nanofibers, are

5

the most studied. For example, many researchers have studied the MWCNT buckypaper (BP)

6

layer as a potential LSP material due to its high conductivity/density ratio [67]. This technique

7

looks very promising as it will also help avoid galvanic corrosion (corrosion to the metal-based

8

LSP due to direct contact with carbon fiber), which is a prevalent problem in aluminum mesh-

9

based LSP systems [68]. However, carbon-nanotube are considered hazardous material [69] and

10

spreading them into the air after lightning hit may cause long-term issues.

11

Wang et al. successfully deposited reduced graphene oxide (RGO) on the composite surface

12

using a percolation-assisted resin film infusion method [70]. They reported a rather high surface

13

electrical conductivity value (440 S/cm), which was relatively very high compared to other

14

reported non-metallic LSPs. The focus of this study was to enhance the surface electrical

15

conductivity of the CFRP substrate to achieve effective lightning-strike dissipation by providing

16

a safe conductive path. The preparation of the RGO layer in this work was similar to the

17

preparation of MWCNT buckypapers in that it is based on the filtration effect, but the electrical

18

conductivity obtained in RGO layers is much higher than the reported electrical conductivity of

19

buckypapers. Authors showed improved performance of the RGO layer as an LSP, but a 23%

20

reduction in residual flexural strength. It is assumed that only improving surface conductivity

21

using an RGO layer was not enough to disperse a large amount of lightning current, as the

22

thickness of the RGO layer was very small and aerial weight might be too little to handle such a

23

high intensity of current (see Figure 4). In the figure, the x-direction is the fiber direction and the

13

1

y-direction is normal to the fiber direction. In the future, it would be worthwhile to study the

2

effect of increased RGO layer thickness on its performance.

3 4

Fig. 4. Cross-section view of the prepared sample using side-light transmission

5

photomicrographs in the y-direction (a and c) and in the x-direction (b) [70]

6 7

Zhang et al. also prepared a thin flexible surface film made of graphene and applied it on

8

the top of the CFRP structure (see Figure 5). They performed LSP simulation and, using image

9

processing, calculated the damaged volume and damaged area after a lightning test [71]. They

10

reported that the control panel (without GO layer) had a damage area and damage volume of

11

1.39 × 104 mm2 and 7.07 × 103 mm3, respectively, which was significantly higher compared to

12

the graphene-coated panel, which had damage area and damage volume of 8.77 × 102 mm2 and

13

3.06 × 102 mm3, respectively. However, the experiment setup and actual CFRP panels were not

14

shown in this work.

14

1 2

Fig. 5. Flexibility of the fabricated graphene thin film [71].

3

Gou et al. used carbon nanofiber paper (CNF) and nickel nanostrands as a surface layer to

4

enhance the surface electrical conductivity of the composite material [72]. They used the

5

papermaking process to prepare a CNF paper which was then incorporated on to the top of the

6

CFRP structure via resin transfer molding. The lightning test confirmed that the lightning strike

7

damage was correlated with the surface conductivity of the composite panel. Figure 6 shows the

8

SEM images of the CNFP-1 at different level surfaces.

9 10

Fig. 6. SEM images of the CNFP-1: (a) top surface at 5 µm; (a0) top surface at 1 µm; (b) bottom

11

surface at 5 µm; (b0) bottom surface at 1 µm [72].

15

1

Han et al. also prepared carbon nanotube paper, namely buckypaper (BP), and studied its

2

effectiveness when combined with an insulating adhesives, as shown in Figure 7 [73]. They

3

bonded BP onto the surface of CFRP laminates with three kinds of adhesives that possessed

4

different electrical conductivities and breakdown strength as shown in Table 2.

5

Table 2. Electrical conductivities and breakdown strength of cured adhesives [73]. Material

6 7 8 9 10 11

Electrical Conductivity (S/m)

Breakdown (kV/mm) 101.5 ± 21.4 2.1 ± 0.2 185.9 ± 7.7

Strength

Pure EP ͠ 2.3 × 10-8 CNTs/EP ͠ 0.4 BN/EP ͠ 6.8 × 10-12 *(EP, bisphenol-A type, EEW = 185 g/eq, Wuxi Resin Factory of Bluestar New Chemical Materials Co., Ltd., China); the conductive adhesive was made of epoxy resin filled by 1.0 wt% CNTs (CNTs/EP); the highly insulating adhesive was composed of epoxy resin with 20 wt% hexagonal boron nitride (BN, av. size = 5 µm, Shanghai ST-NANO Science and Technology Co., Ltd, China) and was denoted as BN/EP.

Han et al. concluded that merely having an insulating adhesive layer is not enough; a

12

combination of an adhesive layer with a enough thickness and BP layer is needed for best LSP

13

results. They based this conclusion on the breakdown strength of the adhesive layer. It is argued

14

that, due to the low breakdown strength of the conductive adhesive, a strong lightning current

15

will puncture the conductive adhesive layer and cause more damage to the structure. An adhesive

16

with high breakdown strength could hinder the transfer of the current in the through-thickness

17

direction. Similar finding is also supported by another recent work by Guo et al. and is discussed

18

separately in later sections [74]. However, as a point of concern, it is important to know that

19

laboratory scale high current generators usually generally work below 20-30 kV, while the

20

natural lightning strike driving voltage can be well above 100 kV. Therefore, the hypothesis of

21

improved LSP behavior using high dielectric materials needs to be reestablished with high

22

voltage induced lightning strike tests. Indeed, it is a fact that during laboratory testing high

23

voltage means low current and vice-a-versa. High voltage (60-200 kV) lightning test and high

24

peak current lightning test (200kA) should be conducted separately. Therefore, LSP based on 16

1

high dielectric strength of an adhesive or separation layer should not be considered an effective

2

way to achieve protection from natural lightning strikes.

3 4

Fig. 7. The BP and the laminate samples: (a) a digital picture of BP, (b) a schematic diagram of

5

the structure of the laminate samples coated with BP. [73]

6 7

Non-metallic LSP layers are promising because they counter the main drawbacks of metallic

8

LSP, i.e., galvanic corrosion and weight. Hence, many researchers dedicate their work to finding

9

a suitable LSP without any metal part in it. Lee et al. used pitch-based carbon fiber paper (PCFP)

10

to protect carbon/epoxy composites [75]. They concluded that the variation in the in-plane and

11

through-thickness thermal conductivities did not affect the damage behavior of structures

12

significantly. They attributed this behavior to a longer thermal diffusion time compared to the

13

total lightning strike duration. The in-plane electrical conductivity of PCFP was identified as the

14

most critical factor in reducing the lightning damage. A high thermal conductivity is considered

15

desirable to dissipate the Joule’s heating quickly in the case of a continuing current component C,

16

but not in the case of fast, transient current components A and D.

17

Kumar et al. also reported in their recent work that an electrically conductive polymer,

18

polyaniline (PANI)-based all-polymeric adhesive layer can be employed as useful LSP

19

technology for high residual strength of the substrate structure even after a lightning strike of 100

20

kA current intensity (see Figure 8) [76]. They attributed this behavior to the self-assembly of 17

1

PANI chains that form a 3D electrically-conductive network and dissipate incident lightning

2

current effectively [77]. The electrical conductivity of PANI-based LSP reported by the Kumar

3

et al. was much less compared to the reported electrical conductivities of RGO and BP-based

4

LSPs, but PANI-LSP performed better dramatically. It is assumed that, in the case of carbon

5

nanomaterial based LSPs, there can be multiple sparks/breakdowns between adjacent nano-fillers

6

as the conduction mechanism is mostly based on percolation threshold, hopping and tunneling

7

mechanism leading to some damage to the structure. In PANI-based LSP, a large amount of

8

PANI filler (15 wt. % of total weight of polymeric layer) was used and direct contact between

9

PANI chains dominated the conduction behavior, which proved to be highly effective in

10

dissipating current without any internal sparks and with reduced resistive heat [78]. The result of

11

thermography confirmed the low heat generation during a lightning strike, and an inspection with

12

a high speed camera showed a fast and effective current dissipation in perpendicular directions

13

[79]. These results established an effective Faraday cage made up of a non-metallic material.

14

However, the thickness of the layer was between 0.2-0.4 mm without any additional

15

supplementary material and hence defies the initial requirement of lightweight LSP. Therefore,

16

minimum required thickness and the effect of other supporting materials (paints, adhesive, etc.)

17

on performance should be considered in future studies.

18

1 2

Fig. 8. Video frames of CFRP specimen during lightning attachment (a) Unprotected CFRPs (b)

3

PANI-layer protected CFRP [76].

4 5 6

Rajesh et al. studied various conductive materials as the coating on CFRP structure for LSP. They used metallic coatings made up of different combinations as shown in Table 3 [80].

7 8

Table 3. Manufacturing details and sample properties of conductive coatings utilized for

9

lightning strike protection in this study. Coating ECF Ag Ag-C

Ag-P

Cu/Sn

Fabrication process ECF overlaid with Cytec Surface Master 905 surfacing film and co-cured Electroless plating; sintered in vacuum for 0 6 h at 120 C [13] Vacuum-assisted transfer of Ag-C particles onto β-stage epoxy surfacing film. This film is placed over CFRP and cured under 0 vacuum at 150 C Spray coating of silver nano particles dispersed in PEDOT:PSS; annealing at 0 200 C for 10 min Cold-spray of 10% copper-tin powder with 0 a gas temperature of 300 and a pressure

Estimated density (g/m3) 2 0.020 g/cm

Thickness (µm) N/A

Avg. 4-point probe resistivity (Ω⋅⋅m) N/A

10.5

~5

0.3

2.4

8-10

0.9

1.7

10-20

28.5

7.5

380

0.12

19

Sn

of 60 psi Cold-spray tin powder with a gas 0 temperature of 300 C and a pressure of 70 psi

7.3

125-350

0.24 (60 psi)

1 2

They compared the damages sustained to CFRP structures after a lightning strike of around 40

3

kA current intensity and found that continuous metallic coatings performed better than hybrid

4

coatings, and the performance of ECF was the best. The damage penetrated the composite

5

substrate in the cases of Ag-P protected, Ag-C protected and neat CFRP composite panels. Ag

6

coating was good enough to protect carbon fibers from damage but showed resin evaporation.

7

Damage was limited to the surface area in the ECF protected sample. They reported that Ag-P

8

and Ag-C protected CFRP samples were more damaged than the baseline CFRP panel, even

9

though the surface conductivity was better with Ag-P and Ag-C. Rajesh et al. provided two

10

hypotheses to explain this behavior. Firstly, they used a marginal experimental error as a reason

11

to discard the Ag-P damage and secondly argued that, in the case of the Ag-C specimen with

12

silver coating on CNF, the lightning current distributed over a larger area on top of the CFRP

13

after LSP succumbs to Joule’s heating and therefore caused a border resin evaporation due to

14

Joule heating. A possible arrest of ejected gases forced them to broader and deeper into

15

composite laminates.

16

conductive coatings for LSP because conductive coatings can add to the damages unless used or

17

applied correctly.

As noted by the Rajesh et al. this is crucial in the development of

18 19

4.1.2 Effect of through-thickness electrical conductivity of CFRP

20

In most cases, resin system is modified to provide or add additional conductive paths to the

21

CFRP structure other than the existing carbon fibers. Many authors have reported additional

22

ways to impart electrical conductivity in the through-thickness direction [81]. Changing fiber 20

1

type, fiber volume fraction, fiber surface modification or modifying the resin system were the

2

common ways to achieve different electrical conductivity in a laminate. However, it was a

3

challenge to detect the exact effects of lightning strike damages when the electrical conductivity

4

of a CFRP laminate was changed without changing the constituent components of the laminate.

5

Kumar et al. reported a way to vary the through-thickness electrical conductivity of CFRP

6

laminate without modifying its constituents (fiber or resin) [79]. They prepared four panels using

7

PANI-based resin and optimized their curing profile to degrade the electrical conductivity of the

8

composites by utilizing the de-doping phenomenon of PANI (see Figure 9) [77]. De-doping is

9

defined as the reduction of electrical conductivity in a PANI polymer due to the detachment of

10

the DBSA molecule from its chains or degradation of its backbone chain. Using this technique,

11

they were able to tune the electrical conductivity by several orders of magnitude, as reported in

12

their other work [82]. The difference in lightning-induced damage was significant when the

13

through-thickness electrical conductivity was reduced. The delamination area between plies

14

increased drastically. This suggests that, with a higher through-thickness electrical conductivity,

15

the current passed over to the next CF layer, which effectively dissipated it using highly

16

conductive carbon fibers. On the other hand, in the absence of sufficient through-thickness

17

electrical conductivity, the first several CF layers of the composite absorb all the current and

18

hence were exposed to higher resistive heat, as captured by a thermal camera during the lightning

19

event (see Figure 10).

21

1 2

Fig. 9. Temperature distribution during current arc attachment to the sample versus specimen

3

length. Number written after CFPANI in the title of the graphs represent the through-thickness

4

electrical conductivity (S/m) values of the CFRP panels.[79]

22

1 2 3

Fig. 10. Damage evaluation using visual and NDI testing. Number written NDT images represent the through-thickness electrical conductivity (S/m) values of the CFRP panels [79]

4 5

Zhao et al. used conductive veils interleaved with a CFRP laminate to increase the through-

6

thickness electrical conductivity [83]. To prepare the electrically conductive veil, they used

7

chopped CF and dispersed them on a releasing film, which was a BMI wet film impregnated

8

onto short fibers. Kumar et al. also used the interleaving method to enhance the through-

9

thickness electrical conductivity of a CFRP laminate by inserting MWCNT buckypaper between

10

CFRP layers [84]. Interleaving conductive layers by replacing the resin-rich insulating area

11

between CF laminate seems to be a straightforward and practical approach to impart through-

12

thickness electrical conductivity [85]. They reported a 697 and 643% improvement in in-plane

13

and through-thickness electrical conductivity by interleaving 7 films of MWCNT buckypaper

14

with 8 CF layers. Zhao and Kumar both confirmed that the composite had an improved

15

resistance to lightning damage with this technique. However, a reduction in the mechanical

16

performance of the composite was also reported. Further investigation of interleaving conductive

17

layers with CF laminate layers without compromising the overall mechanical performance is

18

desired.

23

1

Johannes et al. employed another technique to enhance the through-thickness electrical

2

conductivity of the non-crimp fabric (NCF)-reinforced CFRP composite. They used silver coated

3

yarns with NCF textile. By changing the yarn counts, they successfully modified the through-

4

thickness electrical conductivity and reported a maximum value of more than 100 S/m. They also

5

combined conductive knitting yarn with conductive toughening interleaves and further increased

6

the through-thickness and in-plane electrical conductivity. They successfully demonstrated the

7

superior performance of this technique compared to unprotected composites. However, adding

8

conductive silver knitting yarns to large CF laminates is a high-cost process, which should be

9

considered in the future.

10

In a separate work by Lee et al. [86], the effect of through-thickness stitching on the direct

11

lightning damage done to a NCF-reinforced structural panel was analyzed. It was demonstrated

12

that the electrically conductive through-thickness stitching threads locally improved electrical

13

conductivities in the through-thickness direction, and thus helped in mitigating lightning damage

14

to the composite panel. Another point of consideration could be enhanced interlaminar strength

15

after stitching, which can be an important factor to mitigate mechanical damages due to

16

shockwave or electromagnetic loads.

17 18

4.2 Effect of resin type

19

Kamiyama et al. prepared and studied CFRP using the same type of carbon fibers but three

20

different kinds of resin systems, namely epoxy, bismaleimide (BMI), and polyetheretherketone

21

(PEEK) [87]. They showed that, while all the three resin systems were insulative, the BMI and

22

PEEK-based CFRPs performed better against a simulated lightning strike of 100 kA, compared

23

to the more common epoxy type resin (see Figure 11). They attributed this behavior to the high

24

1

onset temperature of thermal degradation, the char yield, and increased high fracture toughness.

2

The onset temperature of thermal decomposition was 280 °C and the char yield was 75% in the

3

CF/epoxy. While, in the CF/BMI and CF/PEEK, the onset temperatures of thermal

4

decomposition were 370 °C and 530 °C, respectively, and the char yield was 85% and 82%,

5

respectively. However, better dynamic/impact behavior of thermoplastics like PEEK, compared

6

to brittle thermosets resins like epoxy, could be another important aspect to inspect. Better

7

impact behavior can be highly effective at absorbing mechanical loads generated during

8

lightning strike. The authors also mentioned different through-thickness electrical conductivity

9

of the CFRPs, but that was attributed to the different volume fractions of the CFRP structures. In

10

this work, the volume fraction of all three panels was different. Therefore, the distinct

11

contribution of resin type on the electrical conductivity and damage behavior of the CFRPs

12

should be investigated further. Their work established that, in addition to the electrical

13

conductivity of the CFRP, thermal degradation onset temperature and char yield of resin are also

14

essential factors for the performance of CFRPs against lightning strikes.

15

Nano-filler filled resins are also considered a different resin in this section. Therefore, few

16

studies related to this category are also included. Divya et al. first coated the SWCNT with nickel

17

and dispersed them into BMI resin [88]. The composite prepared using this resin was tested

18

against an artificial lightning strike, but no detailed explanation was provided on the waveform

19

of the lightning strike components except that it was conducted as per MIL STD 1757 standard

20

(Zone 2A lightning strike). They also performed a dispersion and surface-coverage study. They

21

confirmed the increased surface conductivity and reported reduced damage to the CFRP sample

22

with Ni-SWCNTs in it.

25

1 2

Fig. 11. Arc attachment surface [87].

3

Yokozeki et al. changed the traditional resin system completely. They invented a new

4

thermosetting resin system based on divinylbenzene [89,90]. Divinylbenzene is known as a

5

cross-linking agent with low viscosity that improves the quality and performance of sheet

6

molding composites. Yokozeki et al. mixed it with a complex of PANI-DBSA and cured it in a

7

manner such that no additional initiator was utilized [91,92]. They showed that a strong protonic

8

acid could be simultaneously used as a curing agent for the DVB and a doping agent for PANI.

9

This finding led to the synthesis of a highly electrically conductive thermosetting resin. They

10

further utilized this matrix to prepare CFRP panels and showed that the CFRP made of the

11

PANI-based resin (CF/PANI) had 5.92 and 27.4 times better electrical conductivity in in-plane

12

and through-thickness directions, respectively, compared with traditional epoxy-based CFRPs

26

1

(CF/epoxy). The CFRP made up of PANI-based resin showed remarkable resistance to the

2

lightning strikes (see Figure 12) [90].

3 4 5

Fig. 12. Specimen damage after simulated lightning current tests: a) CF/epoxy 40 kA (E-1), b) CF/epoxy 100 kA (E-3), c) CF/PANI 40 kA (P-1), and d) CF/PANI 100 kA (P-3).) [90].

6 7

Katunin et al. utilized a similar principle and incorporated a CSA-doped conductive PANI

8

filler into an epoxy (Epidian 6) and amine hardener based resin system [93–97]. They tested

9

samples against a low intensity lightning current, i.e. around 10 kA. Therefore, improved

10

effectiveness of this PANI-epoxy system has yet to be explored.

11 12

4.3 Effect of stacking sequence

13

Work regarding the effect of the stacking sequence of unprotected CFRP laminates was done

14

by Li et al. [98] They reported that the stacking sequence could influence the failure behavior 27

1

significantly in the case of unprotected CFRPs. They concluded that, with specially designed

2

stacking sequences, lamina thickness and weft nylon binder could improve the performance of

3

CFRP structures against lightning strikes. They prepared two types of laminates with a stacking

4

sequence of [452/02/-452/902]s and [302/02/-302/902]s. They argued that the main damaging factor

5

was Joule’s heating, which produces the hot gases at the same intensity of lightning strike. They

6

observed that in 30° specimens, fibers were distributed to form smaller cells compared to 45°

7

specimens. Therefore, hot gases generated due to Joule’s heating got trapped in a small and

8

narrow area, causing severe damage to the specimen (see Figure 13). Another important factor

9

that could be crucial in different layup sequences is the influence of the surrounding return

10

connection in the test rig. The amount of continuous carbon fibers connecting the arc attachment

11

zone to the grounding set up is critical in terms of current dissipation. Carbon fibers are the main

12

current carrying components in CFRP structures and therefore their layup surely affect the

13

current dissipation efficiency of the composite and its eventual performance against lightning

14

strikes. It is also worth to investigate the effect of stacking sequence, when samples are protected

15

by LSP.

16

28

1 2 3

Fig. 13. Damage profile for post-lightning 45 specimen (a) and 30 specimen (b) under 38 kA strike [98]. 4.4 Effect of fiberglass layer and moisture

4

To avoid galvanic corrosion of aluminum based LSP, it is common to have glass fiber layer

5

between the LSP layer and the CFRP substrate. Having a separation layer depends on the

6

industry; some prefer a separation layer, and some don’t. Li et al. studied the effect of the

7

fiberglass layer on the lightning strike damage response of CFRP laminates and concluded that a

8

fiberglass layer does not contribute to the protection of CFRP against a lightning strike (see

9

Figure 14) [21][60]. In this work, “hybrid” was defined as the combination of glass fiber and

10

carbon fiber laminates, and a solely carbon fiber-based laminate was referred as “carbon”. A

11

fiberglass layer was placed only at the top and bottom of the laminate. They compared the

12

performance of both type of laminates in a simulated lightning strike test under dry and wet

13

conditions. Their results provide a compelling argument that moisture significantly affects

14

lightning resistance. CFRP panels with high moisture were more susceptible to damage

15

compared to dry panels (see Figure 15). It is expected that moisture could influence the current

16

penetration ability and could contribute to the generation of hot gases during the lightning arc

17

attachment to the specimen. It is assumed that moisture affected the expansion volume of hot

18

gases and therefore the shockwave also acted over a larger area.

19

Although it is generally believed that fiberglass is used between metal-based LSP (especially

20

for AL-based LSP) and a CFRP substrate to avoid galvanic corrosion and not for lightning

21

protection, [99] another work by Guo et al. [100] reported a different conclusion. They

22

emphasized that a fiberglass isolation layer, used between a metal-based LSP and a CFRP

23

substrate for anticorrosion protection, is capable of improving the performance of EMF LSP.

29

1

They termed this behavior “isolation mechanism”, where the lightning current did not penetrate

2

the insulating fiberglass layer and hence better performance against a lightning strike was

3

achieved. However, work by Gua et al. and Li et al. are contradictory in their finding about the

4

influence of fiberglass on LSP. The authors of the present review article believe that the isolation

5

mechanism from a glass fiber layer will only work in two cases: 1) if the specimen is small,

6

because the lightning current could avoid penetration into the substrate and jump to the

7

grounding rig, and 2) if the lightning strike is composed of low voltage, the dielectric (separation

8

layer) might work. However, in cases of substantially large specimens or in cases of a GFRP

9

layer with conductive impurities (dust, moisture etc.), the isolation mechanism will not work. As

10

soon as the current will enter the specimen, it will cause a bigger damage to the insulation GF

11

layer. Additionally, as the lightning voltage increases (which is usually the case during natural

12

lightning strikes), breakdown of the isolation layer will occur and will cause severe damage. In

13

conclusion, a fiberglass layer should not be considered as the effective way to avoid lightning

14

strike damages to the CFRP substrate structures.

15 30

1 2

Fig. 14. Top view of the hybrid (a)(c) and carbon (b)(d) specimens after 22 kA and 32 kA lightning strike damage in the dry condition [21].

3 4

Fig. 15. Top view of the hybrid specimens after 22 kA (a) and 32 kA (b) lightning strike damage in wet conditions [21].

5 6

4.5 Effect of paint thickness

7

It is common to prime and paint the skin of an aircraft. Painting becomes even more necessary

8

in the case of CFRP frames, to provide a smooth surface on the exterior and protect the outer

9

surface from environmental effects. As reported by F. Lago, F. Siulas, A. Bigand, and many

10

other researchers, the type and thickness of paint are some of the biggest factors in the damage to

11

the substrate structures from lightning strikes [38,43,101,102]. Paints are generally insulative and

12

may influence the mechanism of damage to CFRP structures after lightning strikes. The

13

thickness of these paints are considered, and controlled for, as it can hinder the smooth

14

dissipation of the incident lightning current on the surface. Even with a highly electrically

15

conductive metal-based LSP, an uneven or thick layer of the paint may contribute to significant

16

damages by restricting the fast dissipation of the current. Another contribution of paint thickness

17

is to concentrate the lightning arc. Slow dissipation of an arc current and its high concentration at

18

one location will lead to high heat generation, resulting in structural damage or melting LSP

19

layers. Moupfouma et al. studied the effect of paint thickness on lightning swept stroke damages 31

1

[103]. Lepetit showed how a paint layer has a detrimental effect on the damage because it

2

contributes to enhanced shockwaves due to the concentrated arc [6], and similar findings were

3

obtained by Hirano et al. [52] using a digital image correlation (DIC) method. Figure 16 shows

4

the lightning damage behavior with increasing paint thickness on a CFRP structure.

5

Lago et al. studied the paint thickness effect on the deformation of aluminum-based metallic

6

panels. They utilized a stereo correlation method and tested several paint thicknesses. Their

7

reports showed that the samples with a paint layer thickness of 300µm suffered more deflection

8

than those with only 100 µm. They attributed such behavior to an increase in the magnetic and

9

hydrodynamic pressure, created by the arc.

32

1 2

Fig. 16. Damages due to increased paint thickness [102].

3

Morgan et al. [99] showed, through thermal simulation, that micro-cracking in the paint can

4

cause corrosion of the metal foils and subsequent loss of electrical conductivity of the LSP. This

5

degradation in the electrical conductivity can reduce the performance of EMF LSP drastically.

6

Altogether, the thermal behavior of paints is clearly an important parameter to study.

7 8

5. Conclusion

33

1

Good LSP involves more than merely producing an electrically conductive layer. The

2

dielectric breakdown strength of a separation layer, the electrical conductance path (equally

3

spaced grid or anisotropic) in an EMF-LSP, the thickness of insulative/conductive layers and the

4

areal weight of dielectric coatings also play a significant role in the performance of an LSP. In

5

the case of an unprotected CFRP composite, the through-thickness electrical conductivity of the

6

laminates is as vital as the surface electrical conductivity of the laminates. Stacking sequence (in

7

unprotected CFRPs), interlaminar strength of laminates, resin type, and carbon fiber types also

8

significantly affect the response of the substrate. In the case of a painted panel, the type of paint,

9

dielectric strengths of the paint, and the thickness of the paint play a significant role in damage

10

behavior. Direct lightning damage is predominately dependent on the thermal-mechanical load

11

generated during the lightning event, which includes resistive heating, thermal shock, acoustic

12

shockwave, and electromagnetic forces. An important mechanism, the "isolation mechanism,"

13

has been explored by a few researchers, but further studies are required to establish it. The

14

isolation mechanism is also related to the electric breakdown strength of the isolation layers and

15

hence not recommended to be used as a mean to provide protection against natural lightning

16

strikes.

17

At this moment, carbon filler- and conductive filler-based materials (CNT, graphene, PANI

18

etc.) are the potential candidates of future LSPs. Future research needs to focus on multiple

19

factors, such as lowering the weights of non-metallic LSPs and exploring the compatibility of

20

new LSPs with thermoplastic composites. Also, when performing experimental lightning strike

21

tests to show the effectiveness of any proposed LSP, a few things need to be considered:

22

(a) In actual application, a paint on top of the LSP is required, which eventually will affect

23

the damage mechanism of the CFRP + Proposed LSP. Therefore, painting the CFRP 34

1

samples to mimic the actual scenario is recommended to demonstrate the effectiveness of

2

an LSP.

3

(b) The size of the experimentally tested samples also plays an important role. It is

4

recommended to have a bigger sample to avoid any arc jump that could occur when

5

testing a smaller sample. There is no specific dimension recommended by any standard,

6

but at least 35 cm × 35 cm would be good start.

7

A report by NASA, as cited in ref. [104], is a good document to follow for experiment design.

8 9

Acknowledgment

10

Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and

11

Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00OR22725 with

12

UT-Battelle, LLC.

13 14

References

15

[1]

doi:https://doi.org/10.1016/S0034-3617(07)70051-6.

16 17

[2]

[3]

22

Friedrich K, Almajid AA. Manufacturing Aspects of Advanced Polymer Composites for Automotive Applications 2013:107–28. doi:10.1007/s10443-012-9258-7.

20 21

Sanami M, Ravirala N, Alderson K, Alderson A. Auxetic materials for sports applications. Procedia Eng 2014;72:453–8. doi:10.1016/j.proeng.2014.06.079.

18 19

Roberts T. Rapid growth forecast for carbon fibre market. Reinf Plast 2007;51:10–3.

[4]

Wolfrum J, Schuster TJ, Körwien T. Effects of heavy lightning strikes on pristine and repaired

carbon

composite

structures.

J

Compos

Mater

2017;51:3491–504.

35

doi:10.1177/0021998317690445.

1 2

[5]

Aircraft. J Aerosp Lab 2012:1–13.

3 4

[6]

Lepetit B, Escure C, Guinard S, Revel I, Peres G. Thermo-mechanical effects induced by lightning on carbon fiber composite materials. Int Conf Light Static Electr 2011:1–8.

5 6

Laroche P, Blanchet P, Dellanoy A, Isaac F. Experimental Studies of Lightning Strikes to

[7]

Revel I, Evans S, Flourens F. Edge glow: A combined voltage/power controlled

7

mechanism?

8

doi:10.1109/ICLP.2016.7791388.

9

[8]

[9]

Int

Conf

Light

Prot

ICLP

2016

2016.

Pathania D, Singh D. A review on electrical properties of fiber reinforced polymer

Kawakami H. Lightning Strike Induced Damage Mechanisms of Carbon Fiber Composites. University of Washington, 2011.

12 13

33rd

composites. Int J Theor Appl Sci 2009;1:34–7.

10 11

2016

[10]

Black

S.

Lightning

strike

protection

strategies

for

composite

aircraft.

14

Https://WwwCompositesworldCom/Articles/Lightning-Strike-Protection-Strategies-for-

15

Composite-Aircraft, 2013.

16

[11]

Aircraft and the Challenges of Lightning Testing. J Aerosp Lab 2012:1–10.

17 18

[12]

[13]

23

Dexmet Microgrid Products. Lightning Strike Protection for Carbon Fiber Aircraft Lightning Strike Protection for Carbon Fiber Aircraft. SAMPE Conf., 2007.

21 22

Studies AM, Sciences A, Afb WP. Cloud-to-Ground Lightning in the United States : NLDN Results in the First Decade , 1989 – 98 2001:1179–93.

19 20

Morgan D, Hardwick CJ, Haigh SJ, Meakins a. J. The Interaction of Lightning with

[14]

Long M, Becerra M, Thottappillil R. On the Attachment of Dart Lightning Leaders to Wind Turbines. Electr Power Syst Res 2017;151:432–9. doi:10.1016/j.epsr.2017.06.011.

36

1

[15]

Hanai M, Koyama H, Kubo N, Hashimoto Y, Suzuki I, Ueda Y, et al. Reproduction and

2

Test Method of “FRP” Blade Failure for Wind Turbine Generators Caused by Lightning.

3

Int Conf Light Prot 2006:1509–14.

4

[16]

Madsen SF, Holbøll J, Henriksen M, Bjaert N. Tracking Tests of Glass Fiber Reinforced

5

Polymers as Part of Improved Lightning Protection of Wind Turbine Blades. Light Prot

6

(ICLP), 2004 Int Conf 2004:19–22.

7

[17]

Naka T, Vasa NJ, Yokoyama S, Wada A, Asakawa A, Honda H, et al. Study on Lightning

8

Protection Methods for Wind Turbine Blades. IEEJ Trans Power Energy 2005;125:993–9.

9

doi:10.1541/ieejpes.125.993.

10

[18]

Lightning Protection. Renew ENERGY 2006:4–7.

11 12

[19]

[20]

Karch C, Metzner C. Lightning protection of carbon fibre reinforced plastics — An overview. Int. Conf. Light. Prot., vol. 33, 2016, p. 1–8. doi:10.1109/ICLP.2016.7791441.

15 16

Gagné M, Therriault D. Lightning strike protection of composites. Prog Aerosp Sci 2014;64:1–16. doi:10.1016/j.paerosci.2013.07.002.

13 14

Arinaga S, Inoue K, Matsushita T. Experimental Study for Wind Turbine Blades

[21]

Li Y, Xue T, Li R, Huang X, Zeng L. Influence of a fiberglass layer on the lightning strike

17

damage response of CFRP laminates in the dry and hygrothermal environments. Compos

18

Struct 2018;187:179–89. doi:https://doi.org/10.1016/j.compstruct.2017.12.057.

19

[22]

Wang Y. Multiphysics analysis of lightning strike damage in laminated carbon / glass

20

fiber reinforced polymer matrix composite materials : A review of problem formulation

21

and

22

doi:10.1016/j.compositesa.2017.07.010.

23

[23]

computational

modeling.

Compos

Part

A

2017;101:543–53.

Guo Y, Dong Q, Chen J, Yao X, Yi X, Jia Y. Composites : Part A Comparison between

37

1

temperature and pyrolysis dependent models to evaluate the lightning strike damage of

2

carbon

3

doi:10.1016/j.compositesa.2017.02.022.

4

[24]

fiber

composite

laminates.

Compos

Part

A

2017;97:10–8.

Ogasawara T, Hirano Y, Yoshimura A. Composites : Part A Coupled thermal – electrical

5

analysis for carbon fiber / epoxy composites exposed to simulated lightning current.

6

Compos Part A 2010;41:973–81. doi:10.1016/j.compositesa.2010.04.001.

7

[25]

Kamiyama S, Hirano Y, Ogasawara T. Delamination analysis of CFRP laminates exposed

8

to lightning strike considering cooling process. Compos Struct 2018;196:55–62.

9

doi:10.1016/j.compstruct.2018.05.003.

10

[26]

Wang FS, Yu XS, Jia SQ, Li P. Experimental and numerical study on residual strength of

11

aircraft

12

doi:10.1016/j.ast.2018.01.029.

13

[27]

carbon

/

epoxy

composite

after

lightning

strike

2018;75:304–14.

George N. Szatkowski, Kenneth L. Dudley, Sandra V Koppen JJE and TXN. Common

14

Practice Lightning Strike Portection Characterization Technique To Quantify Damage

15

Mechanisms On Composite Substrates. Int. Conf. Light. Static Electr., 2013, p. Paper No

16

13-51, NF1676L-15995.

17

[28]

TP-2013-401. 2013.

18 19

Boer RK, Smeets M. Lightning strike behaviour of thick walled composite parts, NLR-

[29]

Dong Q, Guo Y, Sun X, Jia Y. Coupled electrical-thermal-pyrolytic analysis of carbon

20

fiber/epoxy composites subjected to lightning strike. Polym (United Kingdom)

21

2015;56:385–94. doi:10.1016/j.polymer.2014.11.029.

22 23

[30]

Dhanya TM, Yerramalli CS. Lightning strike effect on carbon fi ber reinforced composites effect

of

copper

mesh

protection.

Mater

Today

Commun

2018;16:124–34.

38

doi:10.1016/j.mtcomm.2018.05.009.

1 2

[31]

Abdelal G, Murphy A. Nonlinear numerical modelling of lightning strike effect on

3

composite panels with temperature dependent material properties. Compos Struct

4

2014;109:268–78. doi:10.1016/j.compstruct.2013.11.007.

5

[32]

National

Weather

Service

-

NOAA.

Understanding

6

WwwLightningsafetyNoaaGov/Science/ScienceintroShtml

7

doi:https://www.weather.gov/safety/lightning-science-scienceintro.

8

[33]

[34]

SAE ARP-5412B, “Aircraft Lightning Environment and Related Test Waveforms” SAE

Fulmen.

Final

Report

for

Publication,

https://trimis.ec.europa.eu/sites/default/files/project/documents/fulmen_frep.pdf. 2012.

11 12

2017.

Aerospace,. 2005.

9 10

Lightning.

[35]

Chemartin L, Lalande P, Peyrou B, Chazottes A, Elias PQ. Direct Effects of Lightning on

13

Aircraft Structure : Analysis of the Thermal , Electrical and Mechanical Constraints. J

14

Aerosp Lab 2012;AL05-09:1–15.

15

[36]

European Organisation for Civil Aviation Equipment, 1997.

16 17

[37]

Mazur V. The components of lightning. Princ. Light. Phys., 2017. doi:10.1088/978-07503-1152-6ch1.

18 19

EUROCAE ED-84, “Aircraft Lightning Environment and Related Test Waveforms,”

[38]

Sun J, Yao X, Tian X, Chen J, Wu Y. Damage Characteristics of CFRP Laminates

20

Subjected to Multiple Lightning Current Strike. Appl Compos Mater 2018.

21

doi:10.1007/s10443-018-9747-4.

22 23

[39]

ARP5414 Rev. A, “Aircraft Lightning Zoning”, 2005, EUROCAE ED-91, “Aircraft Lightning Zoning,” European Organisation for Civil Aviation Equipment, Paris 1998.

39

2005.

1 2

[40]

Https://WwwBoeingCom/Commercial/Aeromagazine/Articles/2012_q4/4/ 2012.

3 4

Greg Sweers, Bruce Birch JG. Lightning Strikes: Protection, Inspection, and Repair.

[41]

Wang F, Ma X, Zhang Y, Jia S. Lightning Damage Testing of Aircraft Composite-

5

Reinforced Panels and Its Metal Protection Structures. Appl Sci 2018;8:1–11.

6

doi:10.3390/app8101791.

7

[42]

Jia S, Wang F, Huang W, Xu B. Research on the Blow-Off Impulse Effect of a Composite

8

Reinforced

9

doi:10.3390/app9061168.

10

[43]

Panel

Subjected

to

Lightning

Strike.

Appl

Sci

2019;9:1168.

Lago F, Gonzalez JJ, Lago F, Gonzalez JJ, Gleizes A, Gonzalez JJ, et al. Numerical

11

modelling of an electric arc and its interaction with the anode : part II . The three-

12

dimensional model — influence 2005. doi:10.1088/0022-3727/38/2/016.

13

[44]

Karch C, Arteiro A, Camanho PP. Modelling mechanical lightning loads in carbon fibre-

14

reinforced

polymers.

Int

15

doi:10.1016/j.ijsolstr.2018.12.013.

J

Solids

Struct

2018;162:217–43.

16

[45]

Karch C, Paul C. Lightning Strike Protection of Radomes 2019.

17

[46]

Karch C, Honke R, Dittrich KW, Steinwandel J. Contributions of lightning current pulses

18

to mechanical damage of CFRP structures. Int. Conf. Light. Static Electr., 2016.

19

doi:10.1049/ic.2015.0149.

20

[47]

Karch C, Honke R, Steinwandel J, Dittrich KW. Contributions of lightning current pulses

21

to mechanical damage of CFRP structures. Int. Conf. Light. Static Electr., 2015.

22

doi:10.1049/ic.2015.0149.

23

[48]

Foster P, Abdelal G, Murphy A. Understanding how arc attachment behaviour influences

40

1

the prediction of composite specimen thermal loading during an artificial lightning strike

2

test. Compos Struct 2018;192:671–83. doi:10.1016/j.compstruct.2018.03.039.

3

[49]

Sonehara T, Kusano H, Tokuoka N, Hirano Y. Visualization of lightning impulse current

4

discharge on CFRP laminate. 2014 Int Conf Light Prot ICLP 2014 2014;4:835–9.

5

doi:10.1109/ICLP.2014.6973239.

6

[50]

Sousa Martins R, Chemartin L, Zaepffel C, Lalande P, Soufiani A. Experimental

7

characterization of the interaction between high current arc and aeronautical materials.

8

Gas Discharges Their Appl 2016:1–4.

9

[51]

Washington, D.C. Earth’s Electr. Environ., 1986, p. 46–60.

10 11

ARTHUR A. FEW J. Acoustic Radiations from Lightning, National Academy Press

[52]

Yoshiyasu Hirano TS and NT. Experimental Study On Influence Of Shockwave On Composite Lightning Damage. Int. Conf. Light. Static Electr., 2019.

12 13

[53]

Jones DL. Shock Wave from a Lightning Discharge. J Geophys Res 1968;73:3121–7.

14

[54]

Karch C, Schreiner M. Shock Waves from a Lightning Discharge. 34th Int. Conf. Light. Prot., 2018. doi:10.1109/ICLP.2018.8503327.

15 16

[55]

Meredith SL, Earles SK, Kostanic IN, Turner NE. The Magnetic Field Induced by a

17

Lightning Strike’s Indirect Effect Double Exponential Current Waveform. J Math Stat

18

2010;6:221–5.

19

[56]

Karch C, Wulbrand W. Lightning Direct Effects - Magnetic Forces - 2010.

20

[57]

Fu K, Ye L. Modelling of lightning-induced dynamic response and mechanical damage in

21

CFRP composite laminates with protection. Compos Struct 2019;218:162–73.

22

doi:10.1016/j.compstruct.2019.03.024.

23

[58]

Hirano Y, Katsumata S, Iwahori Y, Todoroki A. Artificial lightning testing on

41

1

graphite/epoxy composite laminate. Compos Part A Appl Sci Manuf 2010;41:1461–70.

2

doi:10.1016/j.compositesa.2010.06.008.

3

[59]

Wang FS, Ji YY, Yu XS, Chen H, Yue ZF. Ablation damage assessment of aircraft carbon

4

fiber/epoxy composite and its protection structures suffered from lightning strike. Compos

5

Struct 2016;145:226–41. doi:10.1016/J.COMPSTRUCT.2016.03.005.

6

[60]

Li Y, Li R, Huang L, Wang K, Huang X. Effect of hygrothermal aging on the damage

7

characteristics of carbon woven fabric / epoxy laminates subjected to simulated lightning

8

strike 2016;99:477–89. doi:10.1016/j.matdes.2016.03.030.

9

[61]

Mall S, Ouper BL, Fielding JC. Compression Strength Degradation of Nanocomposites

10

after

11

doi:10.1177/0021998309345337.

12

[62]

Lightning

Strike.

J

Compos

Mater

2009;43:2987–3001.

Raimondo M, Guadagno L, Speranza V, Bonnaud L, Dubois P, Lafdi K. Multifunctional

13

graphene/POSS epoxy resin tailored for aircraft lightning strike protection. Compos Part B

14

Eng 2018;140:44–56. doi:10.1016/J.compositesb.2017.12.015.

15

[63]

micro and nanoscale materials. Adv. Nanotechnol., 2017, p. 1–27.

16 17

Alarifi I, Khan WS, Asmatulu R. Mitigation of lightning strikes on composite aircraft via

[64]

Lombetti DM, Skordos AA. Lightning strike and delamination performance of metal

18

tufted

19

doi:10.1016/j.compstruct.2018.11.005.

20

[65]

carbon

composites.

Compos

Struct

2019;209:694–9.

Guo Y, Xu Y, Wang Q, Dong Q, Yi X, Jia Y. Enhanced lightning strike protection of

21

carbon fiber composites using expanded foils with anisotropic electrical conductivity.

22

Compos Part A 2019;117:211–8. doi:10.1016/j.compositesa.2018.11.022.

23

[66]

CHe H, Gagne M, Rajesh PSM, Klemberg-sapieha JE, Sirois F, Therriault D, et al.

42

1

Metallization of Carbon Fiber Reinforced Polymers for Lightning Strike Protection

2

2018;27:5205–11. doi:10.1007/s11665-018-3609-y.

3

[67]

Zhang J, Zhang X, Cheng X, Hei Y, Xing L, Li Z. Lightning strike damage on the

4

composite laminates with carbon nanotube films: Protection effect and damage

5

mechanism.

6

doi:10.1016/j.compositesb.2019.03.054.

7

[68]

Compos

Part

respect

9

doi:10.1016/j.engfailanal.2015.08.019. [69]

2019;168:342–52.

to

lightning

protection

systems.

Eng

Fail

Anal

2015;57:434–43.

Luleå University of Technology. Researcher warns of health risks with carbon nanotubes. 2011 2019:3–5.

11 12

Eng

Ghavamian A, Maghami MR, Dehghan S, Gomes C. Concerns of corrosive effects with

8

10

B

[70]

Wang B, Duan Y, Xin Z, Yao X, Abliz D, Ziegmann G. Fabrication of an enriched

13

graphene surface protection of carbon fiber/epoxy composites for lightning strike via a

14

percolating-assisted resin film infusion method. Compos Sci Technol 2018;158:51–60.

15

doi:10.1016/J.compscitech.2018.01.047.

16

[71]

Zhang B, Soltani SA, Le LN, Asmatulu R. Fabrication and assessment of a thin flexible

17

surface coating made of pristine graphene for lightning strike protection. Mater Sci Eng B

18

2017;216:31–40. doi:10.1016/j.mseb.2017.02.008.

19

[72]

Gou J, Tang Y, Liang F, Zhao Z, Firsich D, Fielding J. Carbon nanofiber paper for

20

lightning strike protection of composite materials. Compos Part B Eng 2010;41:192–8.

21

doi:10.1016/j.compositesb.2009.06.009.

22 23

[73]

Han JH, Zhang H, Chen MJ, Wang D, Liu Q, Wu QL, et al. The combination of carbon nanotube buckypaper and insulating adhesive for lightning strike protection of the carbon

43

fiber/epoxy laminates. Carbon N Y 2015;94:101–13. doi:10.1016/j.carbon.2015.06.026.

1 2

[74]

Guo Y, Xu Y, Wang Q, Dong Q, Yi X, Jia Y. Eliminating lightning strike damage to

3

carbon fi ber composite structures in Zone 2 of aircraft by Ni-coated carbon fi ber

4

nonwoven

5

doi:10.1016/j.compscitech.2018.11.011.

6

[75]

veils.

Compos

/

8

doi:10.1177/0731684418817144. [76]

Technol

2019;169:95–102.

Lee J, Lacy TE, Pittman CU. Comparison of Lightning Protection Performance of Carbon

7

9

Sci

Epoxy

Laminates

with

a

Non-metallic

Outer

Layer

2018.

Kumar V, Yokozeki T, Okada T, Hirano Y, Goto T, Takahashi T, et al. Polyaniline-based

10

all-polymeric adhesive layer: An effective lightning strike protection technology for high

11

residual mechanical strength of CFRPs ☆2019. doi:10.1016/j.compscitech.2019.01.006.

12

[77]

Kumar V, Yokozeki T, Goto T, Takahashi T, Dhakate SR, Singh BP. Irreversible

13

tunability of through-thickness electrical conductivity of polyaniline-based CFRP by de-

14

doping. Compos Sci Technol 2017;152:20–6. doi:10.1016/j.compscitech.2017.09.005.

15

[78]

Kumar V, Das S, Yokozeki T. Frequency independent AC electrical conductivity and

16

dielectric properties of polyaniline-based conductive thermosetting composite. J Polym

17

Eng 2018. doi:10.1515/polyeng-2018-0031.

18

[79]

Kumar V, Yokozeki T, Okada T, Hirano Y, Goto T, Takahashi T, et al. Effect of through-

19

thickness electrical conductivity of CFRPs on lightning strike damages. Compos Part A

20

Appl Sci Manuf 2018. doi:10.1016/j.compositesa.2018.09.007.

21

[80]

Rajesh PSM, Sirois F, Therriault D. Damage response of composites coated with

22

conducting materials subjected to emulated lightning strikes. Mater Des 2018;139:45–55.

23

doi:10.1016/j.matdes.2017.10.017.

44

1

[81]

Yamashita S, Hirano Y, Sonehara T, Takahashi J, Kawabe K, Murakami T. Residual

2

mechanical properties of carbon fibre reinforced thermoplastics with thin-ply prepreg after

3

simulated lightning strike. Compos Part A Appl Sci Manuf 2017;101:185–94.

4

doi:10.1016/j.compositesa.2017.06.002.

5

[82]

Kumar V, Zhou Y, Shambharkar G, Kunc V, Yokozeki T. Reduced de-doping and

6

enhanced electrical conductivity of polyaniline filled phenol-divinylbenzene composite for

7

potential

8

doi:10.1016/j.synthmet.2019.02.003.

9

[83]

lightning

strike

protection

application.

Synth

Met

2019.

Zhao ZJ, Xian GJ, Yu JG, Wang J, Tong JF, Wei JH, et al. Development of electrically

10

conductive structural BMI based CFRPs for lightning strike protection 2018;167:555–62.

11

doi:10.1016/j.compscitech.2018.08.026.

12

[84]

Kumar V, Sharma S, Pathak A, Singh BP, Dhakate SR, Yokozeki T, et al. Interleaved

13

MWCNT buckypaper between CFRP laminates to improve through-thickness electrical

14

conductivity

15

doi:10.1016/j.compstruct.2018.11.088.

16

[85]

and

reducing

lightning

strike

damage.

Compos

Struct

2019.

Sharma S, Kumar V, Pathak AK, Yokozeki T, Yadav SK, Singh VN, et al. Design of

17

MWCNT bucky paper reinforced PANI–DBSA–DVB composites with superior electrical

18

and mechanical properties. J Mater Chem C 2018. doi:10.1039/C8TC04023K.

19

[86]

Lee J, Gharghabi P, Boushab D, Ricks TM, Lacy TE, Pittman CU, et al. Artificial

20

lightning strike tests on PRSEUS panels. Compos Part B Eng 2018;154:467–77.

21

doi:10.1016/j.compositesb.2018.09.016.

22 23

[87]

Kamiyama S, Hirano Y, Okada T, Ogasawara T. Lightning strike damage behavior of carbon fiber reinforced epoxy, bismaleimide, and polyetheretherketone composites.

45

Compos Sci Technol 2018;161:107–14. doi:10.1016/j.compscitech.2018.04.009.

1 2

[88] Chakravarthi DK, Khabashesku VN, Vaidyanathan R, Blaine J, Yarlagadda S, Roseman D,

3

et al. Carbon Fiber – Bismaleimide Composites Filled with Nickel-Coated Single-Walled

4

Carbon

5

doi:10.1002/adfm.201002442.

6

[89]

Nanotubes

for

Lightning-Strike

Protection

2011:2527–33.

Yokozeki T, Goto T, Takahashi T, Qian D, Itou S, Hirano Y, et al. Development and

7

characterization of CFRP using a polyaniline-based conductive thermoset matrix. Compos

8

Sci Technol 2015;117:277–81. doi:10.1016/j.compscitech.2015.06.016.

9

[90]

Hirano Y, Yokozeki T, Ishida Y, Goto T, Takahashi T, Qian D, et al. Lightning damage

10

suppression in a carbon fiber-reinforced polymer with a polyaniline-based conductive

11

thermoset

12

doi:10.1016/j.compscitech.2016.02.022.

13

[91]

matrix.

Compos

Sci

Technol

2016;127:1–7.

Kumar V, Yokozeki T, Goto T, Takahashi T. Mechanical and electrical properties of

14

PANI-based conductive thermosetting composites. J Reinf Plast Compos 2015;34:1298–

15

305. doi:10.1177/0731684415588551.

16

[92]

Kumar V, Yokozeki T, Goto T, Takahashi T. Synthesis and characterization of PANI-

17

DBSA/DVB composite using roll-milled PANI-DBSA complex. Polym (United

18

Kingdom) 2016;86:129–37. doi:10.1016/j.polymer.2016.01.054.

19

[93]

Katunin A, Krukiewicz K, Turczyn R, Sul P, Łasica A, Bilewicz M. Synthesis and

20

characterization of the electrically conductive polymeric composite for lightning strike

21

protection

22

doi:10.1016/j.compstruct.2016.10.028.

23

[94]

of

aircraft

structures.

Compos

Struct

2017;159:773–83.

Katunin A, Andrzej Ł, Dragan K, Krukiewicz K, Turczyn R. Damage resistance of CSA-

46

1

doped PANI / epoxy CFRP composite during passing the arti fi cial lightning through the

2

aircraft rivet 2017;82:116–22. doi:10.1016/j.engfailanal.2017.09.002.

3

[95]

Katunin A, Krukiewicz K, Herega A, Catalanotti G. Concept of a Conducting Composite

4

Material for Lightning Strike Protection. Adv Mater Sci 2016;16. doi:10.1515/adms-2016-

5

0007.

6

[96]

Katunin A, Krukiewicz K, Turczyn R, Sul P, Bilewicz M. Electrically conductive carbon

7

fibre-reinforced composite for aircraft lightning strike protection. IOP Conf Ser Mater Sci

8

Eng 2017;201. doi:10.1088/1757-899X/201/1/012008.

9

[97]

Katunin A, Krukiewicz K, Catalanotti G. Modeling and synthesis of all-polymeric

10

conducting composite material for aircraft lightning strike protection applications. Mater

11

Today Proc 2017;4:8010–5. doi:10.1016/j.matpr.2017.07.138.

12

[98]

Li Y, Li R, Lu L, Huang X. Experimental study of damage characteristics of carbon

13

woven fabric/epoxy laminates subjected to lightning strike. Compos Part A Appl Sci

14

Manuf 2015;79:164–75. doi:10.1016/j.compositesa.2015.09.019.

15

[99]

Morgan J. Thermal Simulation and Testing of Expanded Metal Foils Used for Lightning

16

Protection of Composite Aircraft Structures. SAE Int J Aerosp 2013;6:371–7.

17

doi:10.4271/2013-01-2132.

18

[100] Guo Y, Xu Y, Zhang L, Wei X, Dong Q, Yi X, et al. Implementation of fi berglass in

19

carbon fi ber composites as an isolation layer that enhances lightning strike protection.

20

Compos Sci Technol 2019;174:117–24. doi:10.1016/j.compscitech.2019.02.023.

21 22 23

[101] Soulas F. Développement d’un modèle mécanique pour la prédiction des dommages de panneaux composites aéronautiques soumis à un choc foudre 2016. [102] Audrey Bigand, Christine Espinosa J-MB. Lightning Surface Explosion Impact Study On

47

1

Damage Generation Into Composite. J. Chem. Inf. Model., Wichita, Kansas: 2019.

2

doi:10.1017/CBO9781107415324.004.

3 4

[103] Moupfouma F. Aircraft Structure Paint Thickness and Lightning Swept Stroke Damages. SAE Int J Aerosp 2013;6:392–8. doi:10.4271/2013-01-2135.

5

[104] George N. Szatkowski, Kenneth L. Dudley, Sandra V Koppen JJE and TXN. Common

6

Practice Lightning Strike Portection Characterization Technique To Quantify Damage

7

Mechanisms On Composite Substrates. J Int. Conf. Light. Static Electr., vol. Paper No 1,

8

Seattle, USA: 2013. doi:10.1017/CBO9781107415324.004.

9

48

Date: Oct 4th, 2019 To, Dr. Uday K. Vaidya, Editor-in-chief Composites Part B: Engineering Dear Sir, There is no conflict of interest with this manuscript. Thanking you, Yours Sincerely, Vipin Kumar, Ph.D. Postdoctoral Research Associate, Material Scientist in Additive Manufacturing and Composite Processing, Polymer Material Development, Oak Ridge National Laboratory, Knoxville, Tennessee, USA. Phone: 865-773-3921 Email: [email protected]