Simulated Lightning Strike Research Articles

Identification of Lightning Strike Damage Severity Using Pulse Thermography Through Integration of Thermal Data

AbstractCarbon fibre reinforced polymers (CFRP) structures, e.g., wind turbine blades, are suspectable to direct lightning strikes due to their semiconductive nature and ability to conduct current. It is critical to identify and evaluate lightning damage as it can cause premature failure of the primary load carrying components. Direct strike lightning damage has been traditionally identified and assessed by ultrasonic (UT) inspection, which is time consuming, usually requires contact, and does not directly provide a measure of damage severity. An appealing alternative to UT is pulsed thermography (PT), which takes minutes to conduct rather than hours and does not require a couplant. The aim of this work is to explore the application of pulse thermography to identify and evaluate the damage state of CFRP panels damaged by simulated lightning strike. A new analysis technique is presented that provides a damage severity metric which allows damage to be categorized, separated, and quantified.

Optimizing lightning location accuracy: A study of propagation velocity and time of arrival in long-range lightning location algorithms

The propagation velocity (v) and time of arrival (Ta) are the primary factors affecting long-range lightning location. In this paper, we have enhanced the Very Low Frequency Long-range Lightning Location Network (VLF-LLN) in China in terms of both pulse pairing methods and location algorithms. Then, the algorithm utilized in the VLF-LLN, and four other long-range lightning location algorithms were compared using lightning strike accidents, simulated lightning strike, and other lightning data as the reference values. Building on this foundation, the discussion centers on the effect of v and Ta on location accuracy, with the results showing that an appropriate Ta yields a more significant improvement in location accuracy compared to v. VLF-LLN uses the peak time of the ground wave as Ta avoids the significant lag caused by sky wave, which is present in other algorithms, and therefore has the best location accuracy with a median location accuracy of 1.81 km.

Intrinsically conductive resin as a functional repair for ECF/CFRP against simulated lighting strike: An experimental study

Non-metallic coatings offer promising applications for protecting carbon fiber-reinforced plastics (CFRP) from lightning, preserving the strengths of epoxy-based composites without galvanic corrosion concerns. This study explores the electrically conductive polyaniline-based resin's dual role: as protective coating and repair solution for traditional ECF/CFRP lightning protection. We evaluated the impact of coating thickness and surface roughness on lightning resistance. A 0.4 mm thick coating with a 400-grit pretreatment demonstrated minimal damage after a −40 kA simulated lightning strike, maintaining 96 % residual strength. Central to this study was the resin's capability as a functional repair for the conventional ECF LSP system. When employed to repair the damaged ECF/CFRP panel, the resin showcased its efficacy by preserving more than 95 % of the system's residual strength even after a subsequent −20 kA lightning strike. These results indicate the proposed conductive resin could be a new practical repair approach for lightning strike damage to the conventional ECF layer.

Superaligned carbon nanotube film/quartz fiber composites towards advanced lightweight lightning strike protection

Due to poor electrical conductivity, carbon fiber-reinforced plastic (CFRP) is easily damaged by lightning strikes. In this paper, highly conductive superaligned carbon nanotube films (SA-CNTFs) and new isolation layers (quartz fibers) were combined to fabricate advanced lightweight lightning strike protection (LSP) composites. We verified that the isolation layer indeed has an LSP effect and demonstrated for the first time that quartz fibers are a better alternative isolation layer material candidate than conventional glass fibers due to their high thermal resistance. The “complementary effect” between the conductive layer and the isolation layer is revealed. The preliminarily optimized laminate composites made of SA-CNTF/quartz fiber can sustain 100 kA simulated lightning strike. Compared with typical CNT-based LSP laminate samples made of buckypaper/Boron Nitride/epoxy layer or SA-CNTF/glass fiber, the weight can be reduced by at least ∼30% and ∼38%, respectively.

Quality Assessment of Low Voltage Surge Arresters

Users expect reliable operation of the surge arrester during overvoltages, which may originate from a switching process or a lightning discharge. The necessary conditions to guarantee these expectations are: appropriate construction of the surge arrester, its production being maintained in accordance with technical standards, and a positive results of the type test. The recipient, especially when purchasing large quantities of the product, can check the final quality of the product through selective testing of samples from the market in order to find the best supplier. This manuscript specifies the basic parameters of low-voltage (LV) surge arresters of four manufacturers. Basic electrical parameters, i.e. leakage current and reference voltage before and after the discharge current of 8 μs /20 μs, were determined for 10 randomly selected surge arresters of each manufacturer. Moreover one sample of each varistor batches was aged by 50 simulated lightning strikes. The obtained results of structural analysis indicate that the crystal structure of the varistor materials changes after ageing process, affecting its electrical properties. The proposed research methodology can be employed as a basis for forecasting the stability of the arrester parameters under operating conditions.

A Comparative Analysis of Carbon Fiber–Reinforced Polymers Subjected to Lightning Damage Tests with Conical Electrodes and Jet Diverting Electrodes

Abstract The results in the damage testing of carbon fiber–reinforced polymers (CFRPs) subjected to simulated lightning strikes are affected by the type of discharge electrodes employed in the laboratory. In this work, two kinds of discharge electrodes, a conical electrode and a jet diverting electrode, were discussed for use in the CFRP-lightning strike testing. The CFRP damage responses to different electrodes were characterized and compared in terms of surface damage area, internal delamination, temperature distribution, pressure distribution, high-temperature gas expansion, and residual flexural strength. The electric arc formed by the conical electrode was more concentrated than that under the jet diverting electrode configuration, thereby producing a smaller surface and internal damage area but a deeper damage depth. The residual mechanical properties of CFRPs tested with the conical electrode decreased significantly under lightning strikes. The discharge channel was uncontrollable by utilizing the jet diverting electrode, and the test results were more dispersed than the results under the conical electrode, which was not conducive to the damage analysis or the repetition of testing. Therefore, the conical electrode is recommended in CFRP-lightning damage testing.

Microstructural characterization and mechanical behavior analysis of 7075-T6 aluminum subjected to simulated lightning strikes

Aircrafts damages caused by lightning strikes have been known since the early days of aviation. However, the physical effects on the aircraft structure are still being investigated. This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6. Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques. Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region. In addition, it was detected the material accumulation occurrence in the damage vicinity of the region. Below the damage, it was found a region where metallurgical changes were identified. The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning. These results are corroborated by the X-Ray Diffraction (XRD) and Rietveld Method (red line) that indicated an increasing in dislocation density and micro-deformation in the material matrix. Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged. The Energy Dispersive X-Ray Spectroscopy (EDXS) and Electron Backscattered Diffraction Test (EBSD) found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 μm in length. They were responsible for nucleation of the microcracks that propagate along the material grain boundaries.

Investigation of thermal degradation and decomposition of both pristine and damaged carbon/epoxy samples with thermal history

Although the investigation of thermal damage in composite materials has increased, the short-term thermal degradation and decomposition mechanisms in a non-oxidative environment have not been well established, as the reported thermal damage results were heavily influenced by the analyses of delicately collected volatiles and the presence of oxygen. The aim of this study, using scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetry, along with kinetics, was to develop a post-mortem solid residual-based microscopic characterising methodology for thermal damage in carbon/epoxy composites induced by simulated lightning strikes. Fibre tufting, resin sublimation and discolouration were found to represent the severity of damage in three damage zones. Whilst fibre tufting was caused not by thermal sublimation but by returning shock waves, resin sublimation and discolouration were dominated by Joule heating. The carbon concentration in the damaged zones was found to radially decrease outwards and vice versa with oxygen. Decomposition started from epoxy dehydration, accompanied by discolouration and formation of water and carbonyl, and released chemical compounds like 2-propenal, acetylene and carbonyl-containing aromatic ether. The successful identification of these unique heating-formed functional groups provided the confirmation of the proposed methodology.

Discharge and ground electrode design considerations for the lightning strike damage tolerance assessment of CFRP matrix composite laminates

Lightning strike damage tolerance of carbon fiber reinforced polymer (CFRP) composites is prone to misinterpretation. This study demonstrates that the design of lightning strike testbeds can be a major cause of the misinterpretation. The risk of misinterpretation originates from the lack of standards clearly defining testbed design requirements including electrode size and ground electrode edge configuration. Here we report the impact of electrode size and ground electrode edge configuration on the damage characteristics of CFRP matrix composite laminates caused by simulated lightning strikes. The results suggest that the level of damage is influenced by discharge current amplitude, discharge diameter, and the existence of electrical insulation covering ground electrode edges. Specifically, the damage increases with increasing discharge current amplitude and decreasing discharge diameter. Most importantly, we report that electrically insulating the edges of ground electrode prevents lightning discharge current from bypassing CFRP matrix composite laminate samples and directly striking the ground electrode. Experiments conducted without electrically insulating the edges resulted in considerably lower sample damages than those resulted from experiments conducted with the electrically insulated ground electrode edges. Our findings suggest that electrode size and ground electrode edge configuration have significant influence on the results of lightning strike experiments.

Dynamic Load Estimation Caused by Simulated Lightning Strike Testing on Aircraft Structural Materials

Dynamic Load Estimation Caused by Simulated Lightning Strike Testing on Aircraft Structural Materials

Damage in CFRP composites subjected to simulated lighting strikes - Assessment of thermal and mechanical responses

Damage is inflicted upon Carbon Fiber Reinforced Polymer (CFRP) composite laminates using simulated lightning strikes to investigate the resulting residual mechanical properties. Seven different CFRP laminate specimens were exposed to simulated lightning strikes using three different electric waveforms. The three waveforms imposed were the 10/350 μs waveform, which simulates the first return stroke during a direct strike according to IEC 61400–24 Ed1.0. The second was a unipolar long stroke component, and the third was a combination of the first return stroke and the long stroke. After exposure to lightning, coupon specimens were prepared for mechanical testing. The test specimens were subsequently subjected to compression and shear loading to determine the post-strike mechanical properties. The compression tests were conducted using uniaxial coupons in accordance with ASTM standard D6641. The shear tests were conducted using V-notch specimens utilizing an Iosipescu test rig in accordance with ASTM standard D5379. Digital Image Correlation was used to capture the strain fields on the surface of the specimens. The results of the material coupon tests are compared with test results from pristine CFRP coupon samples that were not exposed to any electrical current. The shear and compression strengths, compressive and shear stress-strain curves, compressive and shear moduli, and the maximum temperature on the CFRP specimens during lightning tests are presented and discussed. Key results include that the largest reduction of strength occurred in the specimens that were subjected to the largest current and specific energy. The specific energy correlated more closely to the observed reduction of residual strength than the charge, and the damaged specimens displayed a higher degree of nonlinear stress-strain behavior than the pristine specimens.

Lightning strike resistance of an electrically conductive CFRP with a CSA-doped PANI/epoxy matrix

An analysis of a structural damage extent of a developed electrically conductive CFRP composite exposed to the high-current electrical discharges simulating lightning strikes was conducted in order to evaluate its ability of carrying on lightning electrical current and its damage resistance during lightning events. The composite was fully fabricated from organic compounds, i.e. electrically conductive polymer blend of polyaniline (PANI) doped with camphorsulfonic acid (CSA) and epoxy resin, and carbon fabric used both as a mechanical reinforcement as well as supporting electrical conductor for ensuring adequate electrical conductivity and mechanical properties. An investigation of lightning strike resistance was performed during high-voltage and high-current mode tests. For preliminary evaluation the resulting damage was examined using visual inspection. Furthermore, the ultrasonic testing and X-ray computed tomography were applied for evaluation of degradation mechanisms occurring during a typical lightning strike event. The obtained results show that the developed composite is characterized by good electrical conductivity and mechanical properties and may successfully resist high-current impulse discharges typical for lightning strike events. Therefore, the developed composite can be considered asa potential candidate for a lightning strike protection material in aircraft industry and other applications.

Residual mechanical properties of carbon fibre reinforced thermoplastics with thin-ply prepreg after simulated lightning strike

This study experimentally examined the residual mechanical properties of a carbon-fibre/polyamide-6 laminate and randomly-oriented carbon-fibre strand (ROS) thermoplastic composites with thin-ply prepreg after a simulated lightning strike, and compared the results with those of a carbon-fibre/epoxy laminate fabricated from thick-ply prepreg. The damage was characterized by visual inspection, ultrasonic scanning, and optical microscopy. The residual mechanical properties were evaluated using a four-point flexural test. The flexural strength of the carbon-fibre/epoxy laminate was considerably reduced due to delamination, whereas the carbon-fibre/polyamide-6 laminate with a thin-ply prepreg exhibited improved retention of flexural properties. Lightning damage to ROS composites was spread over larger areas and depths, while being scattered and spotted, consistent with superior retention of flexural strength. Moreover, the flexural properties of intact and damaged ROS composites were improved by thin-ply prepreg. These results suggest that the application of thin-ply prepreg to thermoplastics affords composites with superior mechanical properties and lightning resistance.

Effect of thin-ply on damage behaviour of continuous and discontinuous carbon fibre reinforced thermoplastics subjected to simulated lightning strike

This study experimentally investigates the damage behaviour of a quasi-isotropic (QI) laminate of carbon fibre reinforced thermoplastics and chopped carbon fibre tape reinforced thermoplastics (CTT) under lightning strikes. Simulated lightning strike tests were performed and the damage was evaluated using a high-speed camera, ultrasonic testing, and optical microscopy of cross-sectioned samples. The shape of the vaporized resin and projected damage area resulting from the joule heating was dependent on the electrical anisotropy of composite surfaces; the shape of the vaporized resin was circular for QI laminate with thinner prepreg and CTT materials. In addition, the damage could be categorized into three modes: fibre sublimation, resin vaporization, and delamination. Finally, the application of thin-ply prepreg suppressed the projected damage area and the removal of the composite surface due to fibre sublimation and resin vaporization in both samples. Our findings clearly demonstrate the reduction of lightning damage when using thin-ply prepreg.

Effect of hygrothermal aging on the damage characteristics of carbon woven fabric/epoxy laminates subjected to simulated lightning strike

This paper investigates the effect of hygrothermal aging on the damage behavior of two stacking sequenced ([452/02/-452/902]s, [302/02/-302/902]s) carbon woven fabric/epoxy laminates subjected to simulated lightning strike. Damage characteristics are evaluated using visual inspection, ultrasonic scanning and scanning electron microscope. The mechanical properties of post-lightning specimens exposed to the dry and the moisture environments are then studied, respectively. Observations show that enlarged resin damage area and delamination region appear for both of the specimens under moisture condition. Compared to the dry conditioned specimens, the fiber damage shape of the moisture treated ones shows a less sensitivity to stacking sequence, which extends along the ply orientation. SEM results show that the fiber/matrix interfacial bonding is severely degraded by moisture and damaged by lightning strike infliction. Mechanical testing further shows that hygrothermal aging has a more significant influence on the residual strength than modulus for the two stacking sequenced specimens.

Experimental study of damage characteristics of carbon woven fabric/epoxy laminates subjected to lightning strike

This paper experimentally investigates the damage characteristics of two stacking sequenced ([452/02/−452/902]s, [302/02/−302/902]s) carbon woven fabric/epoxy laminates subjected to simulated lightning strike. Characteristics of the damage are analyzed using visual inspection, image processing, ultrasonic scanning and scanning electron microscope. The mechanical properties of post-lightning specimens are then studied. Observations show that as the lightning strike is intensified, an enlarged resin pyrolized area appears majorly along the weft orientation while the delamination region extends equally to both of the warp and the weft direction. The resin/fiber interfacial bonding is severely damaged by a thermal–mechanical effect due to lightning strike infliction. Mechanical testing further shows that the stacking sequence can influence the failure significantly. Compared with prepreg taped material, the restrained damage area due to special designed stacking sequence, lamina thickness and the weft nylon binder make the woven fabric reinforcement a good choice for the fabrication of lightning protection structures.

Monitoring of compression-after-impact testing of CFRP laminates subjected to simulated lightning damage by acoustic emission

The progress of damage during compression-after-impact (CAI) tests of carbon-fibre reinforced plastics (CFRP) laminates made of nanoparticles-coated carbon fibres and subjected to a simulated lightning strike was monitored by acoustic emission (AE). The effects of nanoparticles coating and the degree of damage induced by the simulated lightning strikes on AE activities were examined, with the relationship between the compressive residual strength and AE behaviour being evaluated in terms of AE event counts and the onset of AE activities during the compressive loading. AE monitoring appeared to be useful to assess the degree of impact-damage hence the structural integrity of laminated CFRP structures damaged by lightning strikes.

Development of a Method of Calculating the Melting Characteristics of OPGW Strands Due to DC Arc Simulating Lightning Strike

Some strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. DC arc tests simulating lightning strikes have been performed to obtain the melting and breaking characteristics of OPGW strands. The tests have to be performed under many conditions concerning the arc (e.g., current, duration, polarity, gap length) and the OPGW (e.g., size, type, and number of strands) to clarify the melting and breaking characteristics of the strands. In this paper, the calculations regarding the melting characteristics of strands are performed considering the transferred heat and its area from the arc to the strands under the aforementioned conditions. The melting characteristics of strands are calculated with an arc current of 1-100 kA considering the measured current of actual lightning. The calculation results of the strand melting duration depending on arc current show good agreement with the experimental values obtained in dc arc tests.

A model for process equipment damage probability assessment due to lightning

In recent years, severe natural events raised concern about so-called NaTech accident scenarios: technological accidents caused by the impact of a natural event on an industrial facility or infrastructure. Lightning strikes are one of the most important triggers of NaTech scenarios. Moreover, previous studies showed that lightning strikes are among the main causes of loss of containment (LOC) of atmospheric storage vessels containing hazardous materials. Although the lightning hazard is well known, well accepted quantitative procedures to assess the contribution of accidents triggered by lightning to industrial risk are still lacking. In particular, the approaches to the assessment of lightning strike probability and to the damage caused by lightning strike are mainly qualitative or semi-quantitative and are mostly based on expert judgment. In the present study, a quantitative methodology for the assessment of the equipment damage probability due to lightning is presented. The lightning severity was quantified by means of probability distribution functions of two parameters: peak current intensity and lightning charge. Through the application of a Monte Carlo simulation the expected frequency of lightning strikes on the equipment and the equipment damage probability were determined. The results of the equipment damage model were validated by available experimental data on metal perforation in simulated lightning strikes. The results of the validated Monte Carlo simulations were fit to empirical functions obtaining a simplified model suitable for use in a quantitative risk assessment framework.

Compression-after-Impact Testing of CFRP Laminates Subjected to Simulated Lightning Damage Monitored by Acoustic Emission

CFRP laminates made of nano-particles-coated carbon fibers and damaged by a simulated lightning strike were tested under the compression-after-impact (CAI) mode, during which the damage progression was monitored by acoustic emission (AE). The effects of nano-particles coating on the degree of lightning-damage and the mechanical integrity of composite structures damaged by lightning strikes have been evaluated in terms of AE activities.