Lightning Tests Research Articles

Critical comparison of potential machine learning methods for lightning thermal damage assessment of composite laminates

The present study assesses the potential of using machine learning (ML) methods to predict the extent of lightning thermal damage in fiber-reinforced composite laminates using three supervised machine learning (SML) algorithms: (1) linear regression (LR), (2) decision tree (DT)-based, and (3) MLP models. These models were based on the 10 most significant factors that influence the severity of lightning damage, including three current waveform parameters, four material configurations, and three orthogonal electrical conductivities of each composite. All models demonstrated good performance with coefficient of determination (R2) values between 0.84 ~ 0.96. The multilayer perceptron (MLP) regression model trained with the lightning matrix damage dataset showed the most promising results (R2 > 0.94). Additional hyperparameter optimization was performed to improve the prediction performance of the baseline MLP model. The hyperparameter optimization (Adam optimizer, tanh activation function, and three hidden layers with 234 neurons) slightly improved the performance of the baseline MLP model by ~0.02, but achieved faster convergence. This result suggests that the baseline MLP model trained with the lightning matrix damage dataset is sufficiently accurate and robust. This paper highlights that ML-informed regression models can serve as an efficient first pass-estimator of lightning matrix damage in composite laminates, potentially reducing the amount of extremely time-consuming and expensive laboratory-scale lightning tests or streamlining the development of complex lightning damage models for future design.

Observation and verification of surface electrical explosion driven by radial‐distributed pulsed current in laboratory lightning strike test

AbstractThe laboratory lightning test is essential for assessing the effectiveness of lightning strike protection (LSP). Particularly, direct lightning strike damage can be performed with pulsed current injection into the specimen. This paper focuses on the dynamic process of arc plasma and shock wave behaviour in the vicinity of the ‘strike’ point. A rod‐plate discharge load is built for testing aluminium and coated plate under 40‐kA‐level pulsed current. The visualisation of the luminous discharge plasma and its flow field via high‐speed photography (from different angles) is meticulously designed and implemented, synchronised with electro‐physical diagnostics. The results indicate some new mechanisms for lightning strike damage, apart from the impulse heat loading from the thermal arc. The transient current injection through the arc root concentrates on a thin skin layer (skin‐depth effect), with the radial‐attenuated current density, driving asynchronously electrical explosions on the plate surface. The inhomogeneous Joule heating of the plate leads to outwardly propagating phase transition and shock wave along the conductive surface. In addition, the electro‐thermal instability is observed and regarded as the seed of irregular erosion region. Spectroscopic information reveals two different plasma states of main discharge arc channel and adjacent surface electrical explosion. The correspondence of the physical mechanism of electrical explosion and optical radiation is established. Microscopic images for different regions depict erosion characteristics and summarise influencing factors, further confirming the mechanism above. The research clarifies the role of skin‐depth effect in transaction arc erosion for electrode, complements the electrical explosion theory with unevenly distributed current and helps optimise strategies of LSP.

Lightning Strikes on Metal and Composite Aircraft And Their Mitigation

In this paper, the history of aircraft accidents due to lightning strikes and the statistics of lightning strikes on commercial aircraft are briefly mentioned. The mechanism of interaction between lightning and aircraft is described. Lightning can be simulated in the laboratory. Lightning testing is based on identifying and reproducing the key elements of a typical lightning current waveform; and also on classifying the various parts of an aircraft into different lightning zones. The evolution of aircraft structural materials from wood to metal to composites is traced; some of the newer hybrid materials (‘fibre-metal laminates’) that combine the advantages of metals and composites are mentioned. The lightning mitigation measures implemented by the world’s two major aircraft manufacturers, Airbus and Boeing, are briefly described. Some of the nanomaterials proposed for enhancing the surface electrical conductivity of structural composites are reviewed.

Effect of carbon fiber and thermoplastic resin on laminates under lightning and dielectric strength tests

AbstractThe incorporation of carbon fiber (CF) and thermoplastic resin in wind turbine rotor‐blade represents a challenge for lightning events because CF conducts electricity and the behavior of thermoplastic resins is not well known. A comparative study with laminates with epoxy or thermoplastic resins was performed, using lightning and dielectric strength tests. Lightning tests revealed that resins behaved similarly; the current preferentially flowed in fiber direction and in zones with high contact between fibers (e.g., criss‐crossed fibers at panel edges); the level of through‐thickness damage was inversely related to panel thickness; current flow did not affect the tensile properties in fiber direction, but produced a drop in bending strength; the adequate integration of earth terminals in CF laminates was critical for a proper lightning discharge. In dielectric tests, it was concluded that panels with glass fiber covering CF laminates behaved as through‐thickness insulators; the thermoplastic reduced the laminate's dielectric strength, while the incorporation of CF, or laminate aging in a salt spray chamber showed no difference. Electrical resistance tests showed that the results were not dependent on the type of resin, but on the level of fiber‐to‐fiber and fiber‐to‐terminal contact. The lowest linear resistance was obtained in the longitudinal fiber direction, followed by the transverse and through‐thickness ones.

Lightning damage of composite material driven by multi-physics coupling

Lightning damage of carbon fiber/epoxy composite material results from multi-physics coupling effects including electricity, magnetism, heat and force, etc. Physical behaviors of lightning magnetic fluid and structural response of composite laminate are numerical simulated based on Magneto Hydro Dynamics (MHD) and thermo-electric coupling theory, respectively. The radial basis function (RBF) and high precision dynamic mesh technology are proposed to exchange data of multi-physics and structural response at the interface. Temperature dependent material parameters and latent heat of phase change are considered to reveal lightning damage mechanism of composite laminate. Thermal decomposition, ablation area and depth of composite laminate are predicted by numerical approach and verified through lightning test.

Measurement and analysis of impulse grounding impedance of tower grounding device subjected to artificial lightning M‐component

The impulse grounding impedance of tower grounding device is one of the important factors in the lightning protection evaluation of transmission line. The impulse characteristic test of the actual tower grounding device under lightning was rarely carried out due to the limitation of the test conditions. With the help of Guangzhou Field Experiment Site for Lightning Research and Testing, the artificial lightning characteristic test of the true tower grounding device was carried out. This paper presented partial observation experimental results and related analysis of the impulse grounding impedance of tower grounding device subjected to artificial lightning M-component. A calculation model of the tower grounding device subjected to lightning M-component was established. The changes of the surface soil resistivity under the action of rainwater were taken into account in the calculation. The test data and calculation results of the tower grounding device under the impact of the artificial lightning M-component had achieved good agreement. The non-linear ionization of the soil around the tower grounding device can be ignored, and the real impulse grounding impedance was very close to the DC grounding resistance or power frequency grounding impedance, when the tower grounding device in the experiment was subjected to lightning current M-component.

Lightning Strikes

Lightning testing is innovating to meet the needs of changing aircraft designs and advances in materials

Lightning Protection Design of Transceiver Based on Radio Altimeter

Lightning is a great threat to aircraft flight safety. The lightning protection test of aircraft and the ability of aircraft and its parts to withstand direct and indirect effects are investigated and verified by simulating the real lightning environment in the laboratory. According to the requirements of GJB lightning test, this paper analyzes the lightning grade and introduces several lightning protection designs commonly used in engineer practice.

Effects of Lightning on Pultruded Carbon Fiber Wind Blades

Modern wind turbine blades incur occasional damage from lightning strikes. In non-conductive glass laminates, lightning damage causes severe charring, and is often obvious from visual inspection. In conductive carbon laminates, lightning strikes do not always result in visible damage, and the impact on strength and fatigue resistance is uncertain. Thus, it is difficult to evaluate a carbon fiber wind blade suspected of receiving a lightning strike. This experimental study investigates the effect of electrical current running longitudinally through pultruded carbon fiber wind blade specimens. Testing simulated the worst 1% of lightning strike in terms of peak current, time to peak, and action integral, and the worst 50% of lightning strike in terms of charge transfer. Post-test, specimens were inspected using nondestructive inspection (NDI) methods and were then mechanically tested for ultimate tension and compression, and tension-tension fatigue. Results show that carbon fiber pultrusions withstand severe lightning currents with no visible or NDI-indicated damage. Preliminary structural tests show a decrease in ultimate compressive strength at the most severe lightning test case.

Rocket-Triggered-Lightning Strikes to 10 kV Power Distribution Lines and Associated Measured Parameters of Lightning Current

This article presents an experiment of rocket-triggered lightning to 10 kV power distribution lines and the characteristics of lightning current at Guangzhou Field Experiment Site for Lightning Research and Testing during 2018–2019. The return strokes (RSs) current of the triggered-lightning flashes in this study exhibits a shorter half-peak width and similar risetime and peak current compared with those of subsequent strokes current from natural lightning. The peak current of RSs shows strong power function correlations with charge transfer within 1 ms and action integral within 1 ms of RSs, with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.80 and 0.92, respectively. Besides, the peak current of RSs is proportional to the average rate rise of RSs ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dI</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ). We recommend the double HEIDLER function to simulate the RS current and provide accurate raw data for the study of lightning protection.

Study of Capacitive Coupling Sensor Fused With High Voltage XLPE Cable Joint

A capacitive coupling sensor for partial discharge detection with the fusion of high voltage XLPE cable joint is designed in this paper. The sensor is to address partial discharge signals leading to transmission attenuation and external interference causing poor field detection sensitivity. First, a coaxial waveguide transmission model was established of high-frequency electrical signals in the body and joint. The result showed that the signal transmission attenuation was minimized while the sensor electrodes were closely attached to the outer semi-conductive layer of the body. Second, the equivalent circuit model was constructed of the capacitive coupling sensor fused with the 110 kV straight passing joint. The specific installation location, main structure size, detection bandwidth, and sensitivity of the sensor in the joint area were determined, which was to maximize the coupling output signal amplitude and transfer function amplitude. Finally, a lightning surge voltage test was carried out with the integration of the fusion of the joint voltage thermal cycling. Simulation and measurement show the following: while the sensor is installed in the cable metal sleeve break and the electrodes are closed to the overall semi-conductive layer, there is excellent performance for partial discharge detection in the frequency range of 1–300 MHz, with a sensitivity of 5 pC.

Differences between triggered lightning striking to ground and distribution line inferred from measured currents and electromagnetic fields

In 2018–2019, two types of rocket-triggered lightning tests, that is, striking to ground and distribution line, were conducted in Guangdong, China. The main focus of this paper is to compare the waveform parameters of the return strokes (RS) from the two tests. For current, the 10%–90% risetime of RS from lightning striking to distribution line is 2.4 times higher than that striking to ground, and the differences in the other parameters are small. For close magnetic field, the RS from lightning striking to distribution line have a lower peak (30% lower after considering the peak current) and a larger risetime and half-peak width time; besides, it is necessary to divide the front edge of the close magnetic field waveform into two parts: leader (BL) and return stroke (BRS). For close electric field, the close RS electric field peak (ERS) was less sensitive to distance than the leader electric field peak (EL). For far electric field, the differences in waveform parameters of RS from the two tests were not significant, but after considering the peak current, the normalised initial electric field peak (EP) of RS from lightning striking to distribution line was 14% lower than that striking to ground.

Analysis and practice for observing artificially triggered lightning with a ground-based microwave radiometer

The paper presents a systematic description about the observation scheme analysis and practical observation of artificially triggered lightning with a ground-based microwave radiometer together with other discharging observation instruments at Guangzhou Field Experiment Site for Lightning research and testing in Conghua, Guangdong in the thunderstorm season of the 4 consecutive years from 2016 to 2019. The results from statistical analysis of the brightness temperature data observed from 2017 to 2019 show that: (1) The frequencies such as 28, 30, 51.25 and 51.76 GHz in atmospheric window are more likely to respond with outstanding brightness temperature pulses than other observation frequencies of the radiometer; (2) When the elevation angle is 30°, the observation distance is relatively short (99 m in this study), and the “lightning observation mode” is adopted, the efficiency for a ground-based microwave radiometer to capture the lightning heating effect caused by artificially triggered lightning can be improved; (3) The observation efficiency of the 3 years as a whole is 71.4% but gradually increases year by year; (4) The radiometer observation data can be used to reveal the characteristics of lightning heating effects such as duration and lightning current integral; (5) Combined with the lightning current data measured by a coaxial shunt during the experiment, it was found that the estimated lightning heating effect durations based on 25 artificially triggered lightning observations are well consistent with the lightning current durations, as shown by the correlation coefficient of 0.73. This also implies that the radiometer working on the lightning observation mode presented by this paper can observe the lightning heating effect and estimate its duration.

Validation of a lightning protection system for a fusion-welded thermoplastic composite wind turbine blade tip

Fusion welding for thermoplastic composite wind turbine blades is being investigated as a replacement for adhesives in bond lines to reduce manufacturing time and cost and to promote ease of recyclability. Resistance welding uses an electrically conductive material, such as carbon fiber, embedded in the bond line to heat the joining surfaces and fuse them together under pressure. One main challenge with fusion joining for large wind blades is the ability to use this conductive heating element in the bond line while still protecting the blade from the catastrophic effects of a lightning strike. This paper outlines the design and manufacturing of a lightning protection system for a 5-m-long thermally welded blade tip. The outcomes of high voltage and high current lightning testing applied to the 5 m blade tip show that the proposed design was able to protect the fusion welded bond lines from significant lightning damage.

Optical Progressing and Electric Field Change Characteristics of Altitude—Triggered Lightning Flash With Different Development Paths

AbstractThe characteristics of optical and electric field waveforms from altitude triggered lightning flash at Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during the summer of 2019 are presented. The altitude triggered lightning flash had eight return strokes with nine M‐components along four development paths. And the terminal heights of four paths are over 1,626 m above the ground. Our study presented an arithmetic mean of 0.62 kV/m and an arithmetic mean of 0.63 ms of half‐peak width for 16 initial continuous current (ICC) pulses values, as well as an arithmetic mean of 1.24 kV/m and an arithmetic mean of 0.47 ms of half peak width for nine M‐components values. The average 2‐D speed ranged from 3.80°× 105 to 2.94 × 106 m/s for the attempted leaders and from 1.26 × 106 to 6.96 × 106 m/s for the dart leaders. Basically, the greater the downward leader’s 2‐D propagation speed, the larger the electric field change. The electric field waveform in the rising edge of return stroke can be divided into three parts: “SF” indicates the slow front of the return stroke; “FT” indicates the fast transition of the return stroke; “SS” indicates shoulder structure of the return stroke. The arithmetic mean of SF electric field change is 1.45 kV/m and that of SF risetime is 110.6 μs. The arithmetic mean of the first FT electric field change is 4.71 kV/m and that of the first FT risetime is 1.1 μs. The arithmetic mean of the SS electric field change is 3.89 kV/m and that of the SS risetime is 28.1 μs.

Is Indirect Electrode a Good Choice for Simulated Lightning Damage Tests?—The Effect of Metal Vapor

The laboratory lightning testing commonly uses an indirect electrode as the current injection configuration to restraint the electrode jet for evaluation of lightning strike damage tolerance of aircraft materials. Such an indirect electrode configuration requires using a conductive ignition wire to initiate the arc. This work discusses the influence of added metal vapor, produced due to evaporation of the ignition wire, on the electric-arc-induced heat flux and current density as well as the material damage through numerical modeling and simulated experiments. Metal vapor originated from the requisite ignition wire considerably alters the net emission coefficient and transport properties of the arc, leading to questionable testing results and unreliable guidance for lightning protection design. The damage depth of an aluminum alloy is affected by 312.5% due to the changes in the net emission coefficient and thermal conductivity. The damage area shows moderate changes due to a Gaussian-shape decrease profile of heat flux and its insensitivity to the changes in the net emission coefficient. The direct electrode configuration is promising to avoid the use of ignition wire and produce material damage representative of actual damage caused by natural lightning. The results and discussions provide insights into the design of improved lightning certification tests.

Statistical Characteristics of Current and Magnetic Fields at Close Distances From Triggered Lightning

The statistical characteristics of current and magnetic field waveforms from triggered lightning experiments at the Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during the summer of 2019 are presented in this article. The parameters of statistical distributions of return stroke current are analyzed for peak current, 10–90% risetime, half-peak width, and interstroke interval. The geometric mean of peak current is 12.4 kA. The time-related parameters of the magnetic field at different distances are reported and compared to previous reports of close distances, which indicate the magnetic field 10–90% risetime and 30–90% risetime increase with the distance. The geometric means of the magnetic field peak at 58, 90, and 1600 m are 121.1, 66.2, and 1.85 μT, respectively. The magnetic field shows a positive linear relationship with current peak values. The analysis of all magnetic field peaks at different distances suggests a distance dependence of r −0.92.

Characterization of electric field waveforms from triggered lightning at 58 m

This paper statistically analyzed electric field waveform parameters of 56 negative triggered lightning return strokes at the distance of 58 m obtained at Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during the summer of 2019. In addition, the correlation between the electric field peak and the current peak at the bottom of the lightning channel has also been analyzed. The statistical results in this paper extend the database of detailed close electric field waveform parameters of triggered lightning leader/return stroke.

Experimental and numerical analysis of damage mechanisms for carbon fiber-reinforced polymer composites subjected to lightning strikes

This study aims to reveal the damage properties and mechanism of carbon fiber-reinforced polymer (CFRP) composites subjected to lightning current component A by artificial lightning tests and simulation analysis. The lightning strike process was observed by using a high-speed camera and infrared temperature measurements. The surface damage and internal damage were inspected via ultrasonic and 3D X-ray scanning. The damage behavior of CFRP composite was deduced and the damage regions were quantitively analyzed by detecting the surface morphology and microstructural changes and analyzing the lightning strike process. The results indicated that the lightning-induced damage included lightning attachment damage due to direct contact with the lightning arc, laminate peeled-off damage caused by the explosive gas impact, and internal delamination induced by expanding pyrolysis gas. A coupled thermal-electric CFRP model, which first introduces the dynamic conductivity of CFRP materials, was established. The comparison results indicated that the Joule heating-based numerical model can simulate the evolution of thermal damage well, although the laminate peeled-off damage resulting from the mechanical impact was not included in the simulation scope. A temperature field criterion and a pyrolysis degree field criterion were proposed and verified for evaluating in-plane and in-depth damage with acceptable deviations.

Vehicle Adaptive Rear Combination Light with Non-Replaceable Light Sources

Currently, due to the increase in the average speed of vehicles to ensure their visibility, the luminous intensity of their lightning equipment is constantly increasing, that can lead to blindness of other road users, especially at night. On the other hand, if you do not increase the luminous intensity if lanterns, a vehicle will not be noticeable in difficult road conditions (fog, rain, dust) and it can cause an accident. To eliminate this contradiction, a fundamentally new modular design of the adaptive rear combined vehicle light with non-replaceable light sources based on single powerful light emitting diodes and effective secondary optics of large diameter has been developed in the paper. The design provides for the use of an integrated microcontroller to control luminous intensity of its lights, depending on the conditions of external illumination, braking dynamics of a car and surface condition of a lamp diffuser with the possibility of transmitting data via a CAN-bus. Thanks to the built-in microcontroller, the developed flashlight is suitable for installation on vehicles without an on-board computer. These properties allow the flashlight to ensure visibility of a vehicle, and to avoid blinding the remaining road users. The design of the adaptive lamp is small in thickness (up to 40 mm), high luminous efficiency (at least 85 %) and reliability. The conducted lightning tests have shown that the developed lamp fully complies with UN Regulation No 6, 7, 23, 38, 48. The design has been compared with existing analogues of foreign production, which showed that such a lamp consumes less energy (30 %) and has a lower probability of failure due to the use of high-power LEDs used as a light source.