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Multiphysics Analysis of Lightning Strike Damage in Laminated Carbon/Glass Fiber Reinforced Polymer Matrix Composite Materials: A Review of Problem Formulation and Computational Modeling
Abstract
Laminated carbon/glass fiber reinforced polymer matrix composite structures experience rapid temperature rise, resin decomposition, delamination, thermal ablation, and possible dielectric breakdown subjected to lightning strikes. The predictive analysis of these damage is challenging due to the complicated electric-thermal-mechanical-chemical coupling effects. In this paper, the basic physics, problem formulations, and numerical approaches for such multiphysics analysis are thoroughly reviewed. Limitations of the existing problem formulations and numerical approaches are extensively discussed. Possible solutions to overcome those limitations and future directions on improving the fidelity and accuracy of such predictive analysis are also provided. In addition, part of the material properties that are required for these analyses, such as the temperature-dependent thermal, electrical, and mechanical properties of the composite lamina, the fracture properties of the interface resin, and the dielectric breakdown strength of the composite laminate are collected from various sources and are provided in this paper.
... On the one hand, due to the latent heat of phase transition, the local OGW region that reaches phase transition temperature needs to absorb additional energy [15]. On the other hand, once the material is vaporized, it is separated from the original structure, and the mass loss of OGW is formed [16]. The evolution of this dynamic structure is also not negligible. ...
... While for the simulation of mass loss, there are the Arbitrary Lagrangian-Eulerian method (ALE) and element deletion method (EDM) [16]. ALE is moving mesh method, which can be adopted effectively for the single substance. ...
... However, it cannot be applied to the interface between different solids [13]. While for EDM, the pre-set elements are removed in real time once their temperatures exceed the vaporization temperature [16]. In this situation, the element region needs to be established beforehand during the geometric modeling. ...
... Due to the electrical properties of polymers, damage (which sometimes cannot be detected through visual inspection) is prone to occur whenever these components are struck. Therefore, evaluating the effect of this occurrence on the structural integrity and fatigue life of polymer-matrix composite parts is essential [53,54]. Whenever a composite structure is struck by lighting, a very high current channel is created and absorbed by the material [53]. ...
... Therefore, evaluating the effect of this occurrence on the structural integrity and fatigue life of polymer-matrix composite parts is essential [53,54]. Whenever a composite structure is struck by lighting, a very high current channel is created and absorbed by the material [53]. Polymeric matrices usually present poor conductivity, leading to a large temperature increase in zones neighbouring the attachment point due to the Joule effect [54]. ...
... With the high level of delamination, crack growth mechanisms and matrix degradation, the fatigue life of composites subject to these types of events is drastically reduced. Despite the majority of the damage being caused by these factors, many other effects need to be considered, such as fibre breakage, quick changes of electric and mechanical properties as well as very high-temperature gradients through different directions and layers [54,55], making this type of event challenging to simulate using commercial finite element software [53,55]. Despite some solutions that have been proposed to mitigate the problem, such as the inclusion of electrical conductive nanoparticles in the polymer or the use of better conductive matrices, their maturity and ease of manufacturing are still the limiting factors that hamper their wide-scale implementation [56]. ...
Polymer-matrix composites are widely used in engineering applications. Yet, environmental factors impact their macroscale fatigue and creep performances significantly, owing to several mechanisms acting at the microstructure level. Herein, we analyse the effects of water uptake that are responsible for swelling and, over time and in enough quantity, for hydrolysis. Seawater, due to a combination of high salinity and pressures, low temperature and biotic media present, also contributes to the acceleration of fatigue and creep damage. Similarly, other liquid corrosive agents penetrate into cracks induced by cyclic loading and cause dissolution of the resin and breakage of interfacial bonds. UV radiation either increases the crosslinking density or scissions chains, embrittling the surface layer of a given matrix. Temperature cycles close to the glass transition damage the fibre–matrix interface, promoting microcracking and hindering fatigue and creep performance. The microbial and enzymatic degradation of biopolymers is also studied, with the former responsible for metabolising specific matrices and changing their microstructure and/or chemical composition. The impact of these environmental factors is detailed for epoxy, vinyl ester and polyester (thermoset); polypropylene, polyamide and poly etheretherketone (thermoplastic); and for poly lactic acid, thermoplastic starch and polyhydroxyalkanoates (biopolymers). Overall, the environmental factors mentioned hamper the fatigue and creep performances, altering the mechanical properties of the composite or causing stress concentrations through microcracks, promoting earlier failure. Future studies should focus on other matrices beyond epoxy as well as on the development of standardised testing methods.
... Significant increases are observed when the temperature is larger than ~400 °C [100], [103], [105]- [108]. However, a weakly coupled formulation of the electromagnetic-thermal problem, i.e., no dependence of the electrical conductivity on temperature, should allow a realistic description of the lightning thermal damage at the EB interface of wind turbine blades. ...
... thickness directions, respectively [30], [31], [33], [100], [103], [105]- [108], [123]. Several studies have presented experimental procedures to characterise the orthotropic electrical conductivity tensor of CFRP materials, such as [30]- [33], [124]. ...
... This produces several electrical contact points between the carbon fibres that allow conduction along both transverse and through-thickness directions [29]. Therefore, it is common practice in numerical simulation studies, e.g., [31], [108], [144], to assume a relative permittivity of 1 ...
Modern wind turbine blades are equipped with a lightning protection system to intercept the lightning and conduct its current, preventing the direct attachment to internal conductors. In such conditions, resin thermal degradation develops at the equipotential bonding (EB) connections between down conductors (DCs) and carbon fibre reinforced polymer (CFRP) spars. This problem was investigated in this work by combining experimental studies and finite element method (FEM) simulations. The experimental work focused on the characterisation of the input material properties to be used in the FEM models. An experimental-numerical procedure was established to determine the electrical contact resistivity of EB joints. Besides, the thermal degradation of a commercial epoxy was studied to determine its reaction kinetics. The developed FEM models solve a weakly coupled formulation of the electromagnetic-thermal problem to predict lightning current paths and thermal damage at the bonding interfaces. The validation of the models against conducted current test data showed that they can assist in the design of EB joints. High current densities and temperatures were predicted at the sparking locations found during the test, which allowed a qualitative prediction of potential thermal degradation areas upon the solution of the Arrhenius equation. In addition, such models can be used to assess the potential risk of flashover between the blade conductors due to high electric fields. Finally, typical EB materials were compared using the developed FEM models to provide guidelines and suggestions for the implementation of EB joints. It was seen that materials with high in-plane electrical conductivities, such as ECF and BIAX CFRP, can reduce the electric field below the insulation breakdown strength and prevent flashovers. Besides, hot spots at the bonding interfaces can be controlled by changing the arrangement of the EB layers, or by using a material with low contact resistivity and high thermal diffusivity like ECF.
... Ogasawara et al. [19] were some of the first authors to produce a detailed, coupled thermal-electric lightning strike simulation. The authors were able to generate a temperature distribution through the specimen and attempted to correlate these temperatures with delamination and resin damage [19], [20]. Despite many of the key physics (plasma, pressure and thermal-expansion) not being considered here, this work has formed the basis for the majority of ensuing simulation based research [12], [13]. ...
... More recently all of the key physics involved in a strike have been included in some form [13], [27], [29], [31] and most recently effects such as material heating and strain rate have been considered [13]. In 2017, Wang [20] reviewed the physics, problem formulations, and numerical approaches for multiphysics analyses for simulating lightning strikes. Limitations, possible solutions and numerical approaches were discussed. ...
... Abdelal and Murphy [18] were the first authors to use temperature-dependent data, generated in the 1980's, in separate studies by Griffis et al. [51] and Fanucci [52]. There have been very few updates to this data since these publications [20] and this same set of temperature dependent data has been used by a number of authors [18], [29], [35]- [38] while a further sub-set of researchers have used this data with minor adjustments to throughthickness electrical conductivity [12], [13], [15], [17], [26], [27]. ...
Aircraft are increasingly being made of electrically resistive composites, rather than conductive metals. Therefore, it is important to analyse the damage caused by a lightning strike. Given the benefits of simulations over experimental analysis in terms of cost and specialist test infrastructure required, simulations have become increasingly important in the analysis of lightning strike damage. Preceding review articles have focused on lightning strike protection of composites and an initial review of the physics, problem formulations, and numerical approaches for multiphysics analyses for simulating lightning strikes. However, none have systematically critiqued and contrasted the lightning strike simulations used in literature to date. Therefore, this review paper focusses on the modelling and simulation approaches within literature, paying particular attention to their material properties, construction, loading strategies, meshing approaches, solutions and results. The current and proposed lightning strike modelling approaches are discussed along with their current limitations and future challenges.
... There are several types of damages in composite laminate structures [15] amongst which delamination is dominant in applications, such as drilling [16], impact [17], fatigue [18], and some other operations [19,20]. Delamination will affect the properties and change the dynamic characteristics of structures [21,22], including reducing natural frequency [23], change mode shape [24,25], and enhancing deformation [26,27]. ...
... Therefore, there are 16 equations from (2-5), (2-6), (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), that used to develop the 'free mode' model. ...
... 19, which means the point Ls=0.20L is more sensitive to the delamination size with 1Hz excitation. The FEM result is also close to the analytical result based on the two models which show that the proposed method result is credible. ...
This research focuses on the investigation of delamination assessment in composite structures by using methods based on structural dynamic responses. Delamination is a common type of damages for composite structures in applications. It is necessary to detect and assess the delamination in composite structures to ensure the composite structures operating and maintaining. However, the dynamic responses of structures with delamination may be difficult to be analyzed due to the complexity of composite structures as the result of the different properties of materials in the composite structures. Therefore, it is necessary to develop effective methods for delamination analysis and assessment, which will be investigated in this research. To address these problems, this research aims to: 1. Develop new methodologies for dynamic analysis of delaminated composite structures to analyze the effect of delamination based on the evaluation of the vibration characteristics of composite structures with different delamination configuration; 2. Develop effective methodologies to detect and assess delamination in composite structures based on the dynamic responses by using the phase space topology analysis to improve the sensitivity and robustness of delamination assessment for composites structures; To achieve these two aims, the research content and novelty are stated as: 1) Firstly, this study proposes a method based on the Green’s function to develop analytical models of delaminated structures that can be used to investigate the effect generated by delamination on the vibration characteristics. The accuracy of this developed model to describe the vibration characteristics of delaminated beam structures especially under forced excitation is verified by the comparison with other types of models, including the numerical models. The result demonstrates the accuracy and advantages of the proposed analytical model to investigate the effect of delamination on the vibration characteristics of the beam structures under excitation of various frequencies with different delamination configurations, such as size, location, and depth. It should also be noted that the proposed modeling method is demonstrated useful to investigate the vibration characteristics of various measurement locations, which is important for the delamination assessment based on the dynamic responses of structures. 2) Secondly, based on the developed analytical model by using the Green’s function, the investigation has been done for the effect of various measurement locations on the sensitivity to the particular vibration modes with various delamination configurations. Based on this situation, the methodology based on the modal observability (Mn) and the spatial observability (So) is proposed to optimize the structural sensor locations to make the measurement focusing on the vibration modes sensitive to the delamination, which can improve the delamination assessment. The result demonstrates that the proposed methodology is effective to determine the sensor locations which can provide strong signals with sufficient distributions of the particular vibration modes sensitive to the delamination. So the optimization can improve the delamination assessment effectively based on providing sensitive vibration measurement locations. 3) Thirdly, a methodology based on the phase space topology analysis of the dynamic signals measured from the structures is proposed to assess delamination in composite structures. The phase space topology structures are evaluated by using a method named phase space reconstructed (PSR) method based on the dynamic signals measured by the dynamic sensors. A feature named the change of phase space topology (CPST) is used to describe the effect of delamination on the phase space topology structures. The result demonstrated that the phase space topology structures and CPST are sensitive to delamination. The robustness of the proposed feature to the measured noise has also been tested, which shows that the proposed method and feature have sufficient robustness to the measured noise in applications. This research also improves the methodology to assess delamination based on the phase space topology analysis by incorporating with the wavelet packet decomposition. The wavelet packet method can decompose a dynamic signal into several sub-signals in different frequency ranges, which may contain different local information relevant to the delamination. Then the phase space topology structures and the CPSTs of different sub-signals can be evaluated and investigated to analyze the local information. The phase space topology structures of sub-signals decomposed by the wavelet packet method can describe the change of energy distribution of sub-signals in different frequency ranges generated by the delamination. The possibility of the proposed method is demonstrated by the simulation and experiment and the proposed features will be used in the following work; 4) Based on the previous work, a method by using the artificial neural network (ANN) based on the phase space topology analysis to estimate delamination in structures is proposed tested. The ANN can be used to describe the relationship between the delamination and vibration characteristics to estimate the delamination without mechanism analysis for composite structures. The CPSTs of original signals and sub-signals decomposed by the wavelet packet method are used as input factors for the ANN to assess the delamination in composite structures. The accuracy of the ANN for the delamination assessment can be enhanced by training the ANN with more cases. The possibility and the potential are tested in this research. The different performances for various delamination parameters estimate are also analyzed, which shows that the performance for various delamination parameter assessments is different due to the different effect of delamination on the input factors. Furthermore, the performance of delamination assessment by using the ANN with different input factors is investigated to analyze the effect of input factors on the delamination assessment performance and find the best input factors for ANN in this research. The results show the CPSTs of sub-signals generated by wavelet packet decomposition are the best input factors because this type of feature can provide more information with high sensitivity and good robustness to the measurement noise. In conclusion, this research will provide a systematic study for the improvement of delamination assessment and development of applicable methods for composite structures based on the dynamic signals by analyzing the phase space topology structures combined with wavelet packet decomposition and ANN. Moreover, the theoretical analysis and optimization for dynamic signal measurement are analyzed to provide explanation and support for the delamination assessment. The potential of the proposed methods for other types of damage in composite structures and other applications are also mentioned in this research.
... Moreover, a surface radiation boundary condition needs to be applied to account for the radiative heat exchange between the external surfaces of the CFRP composite specimen and the ambient environment. A convective heat boundary condition may not be necessary due to the extremely short duration of the lightning strike [19,56]. For models that couple the electric-thermal response with the mechanical response, additional displacement boundary conditions need to be applied, which depends on whether the four edges are clamped or simply supported or having a mix of both [57][58][59][60][61]. ...
... Moreover, a surface radiation boundary condition needs to be applied to account for the radiative heat exchange between the external surfaces of the CFRP composite specimen and the ambient environment. A convective heat boundary condition may not be necessary due to the extremely short duration of the lightning strike [19,56]. For models that couple the electricthermal response with the mechanical response, additional displacement boundary conditions need to be applied, which depends on whether the four edges are clamped or simply supported or having a mix of both [57][58][59][60][61]. ...
Lightning strike events pose significant challenges to the structural integrity and performance of composite materials, particularly in aerospace, wind turbine blade, and infrastructure applications. Through a meticulous examination of the state-of-the-art methodologies of laboratory testing and damage predictive modeling, this review elucidates the role of simulated lightning strike tests in providing inputs required for damage modeling and experimental data for model validations. In addition, this review provides a holistic understanding of what is there, what are current issues, and what is still missing in both lightning strike testing and modeling to enable a robust and high-fidelity predictive capability, and challenges and future recommendations are also presented. The insights gleaned from this review are poised to catalyze advancements in the safety, reliability, and durability of composite materials under lightning strike conditions, as well as to facilitate the development of innovative lightning damage mitigation strategies.
... CFRP is one of the most desirable materials for space industries due to its high specific stiffness. It is 30% more strong, but five times less in weight compared to traditional space material like Kovar and Invar, as shown in Table 1 (Yeqing, 2017;Davis, 2000). For the interplanetary missions, where the mass is a critical factor of design criteria, CFRP is most advantageous. ...
... Physical properties of traditional space materials and CFRP(Yeqing, 2017;Davis, 2000) ...
High specific stiffness materials are used to design the space payload components. These components should sustain the extreme environmental conditions throughout their life cycle, without failure. Space missions need lightweight materials which are mechanically strong with high thermal and electric conductivities. Carbon fiber reinforced polymer (CFRP) offers considerable mass saving and high strength, which is widely used for space payload components. However, it has limitations to replace the traditional space-qualified materials due to its low conductivity. Carbon Nanotubes (CNTs) are efficient with greater electrical and thermal conductivities. For CNTs to be seen as effective reinforcements for attaining high strength and conductivity of polymer composites, they need to meet the criteria of being well-dispersed by the solution mixing method. The quality of the CNT nanocomposite relies upon several parameters like the type of CNTs, purity, aspect ratio, amount of loading, alignment and interfacial adhesion between the nanotube and polymer. The performance of the CNT-CFRP composite depends on the successful execution of the processing technique. It has been intended in this review paper to highlight the enhancement of the mechanical, thermal and electrical properties of the composite, and the challenges in achieving it. An attempt has been made to optimize the process parameters to fabricate space payload components which can be excellent alternatives to the existing high-density materials. Moreover, this review research is the need of the hour for prominent space agencies such as ISRO and NASA for their future inter-planetary missions, where payload weight needs to be kept light without making any compromise on the performance index.
... To provide a rough estimate on the temperature, we can refer to the delamination damage in the upper CFRP composite adherend. As shown in Fig. 5, the most severe interlaminar delamination occurred between the second and third ply of specimen 4. It is widely recognized that the delamination in CFRP composites is caused by the thermal decomposition of the epoxy resin between interlaminar layers [18,19]. Note that the onset temperature for the decomposition of epoxy resin is about 300 °C [18,19]. ...
... As shown in Fig. 5, the most severe interlaminar delamination occurred between the second and third ply of specimen 4. It is widely recognized that the delamination in CFRP composites is caused by the thermal decomposition of the epoxy resin between interlaminar layers [18,19]. Note that the onset temperature for the decomposition of epoxy resin is about 300 °C [18,19]. Since the most severe delamination only reaches the third layer of the 9-layer ...
Adhesive bonding to join fiber reinforced polymer matrix composites holds great promise to replace conventional mechanical attachment techniques for joining composite components. Understanding the behavior of these adhesive joints when subjected to various environmental loads, such as lightning strike, represents an important concern in the safe design of adhesively bonded composite aircraft and spacecraft structures. In the current work, simulated lightning strike tests are performed at four elevated discharge impulse current levels (71.4, 100.2, 141, and 217.8 kA) to evaluate the effects of lightning strike on the mechanical behavior of single lap joints. After documentation of the visually observed lightning strike induced damage, single lap shear tests are conducted to determine the residual bond strength. Post-test visual observation and cross-sectional microscopy are conducted to document the failure modes of the adhesive region. Although the current work was performed on a limited number of specimens, it identified important trends and directions for future more comprehensive studies on lightning strike effects in adhesively bonded composites. It is found that the lightning strike induced damage (extent of the surface vaporization area and the delamination depth) increases as the lightning current increases. The stiffness of the adhesive joints and shear bond strength did not show a clear correlation with the lightning current levels, which could be due to many competing factors, including the temperature rise caused by the lightning strike and the surface conditions of the adherends prior to bonding. The failure modes of the adhesive regions for all specimens demonstrate a mixed mode of adhesive and cohesive failure, which may be due to inconsistent surface characteristics of the adherends before bonding. The energy absorbed during the lap shear tests generally increases as the lightning current increases.
... The direct damage effect is one of the deleterious effects of lightning, for which the overloads of the intense current and voltage injection, strong electromagnetic forces, highpressure wave impacts, and massive heat infliction are the damage sources for lightning-attached materials [9]- [14]. For materials (e.g., metallic materials and fiber-reinforced polymer matrix composite materials), the damage responses, such as the damage area, depth, delamination, and residual strength, are key parameters in lightning testing [15], [16]. Limited by the uncertainty in natural lightning, the simulated lightning technology is a feasible method for lightning certification tests on materials. ...
... The electric field strength affects the subsequent dynamic electron density and the associated arc radius. Our previous study shows that the electrode in a semiellipsoidal shape [see Fig. 16(a)] can smooth the variation in the surface electric field and thereby alleviate material erosion on the electrode surface [15]. In the experiment, when testing with higher lightning arc currents (≥200 A), the extremely high-temperature rise on the anode can still exceed the melting point near the head region. ...
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.
... They discovered a significant inverse correlation between the electrical conductivities and the extent of thermal damage. Several researchers predicted the extent of damage caused by a lightning strike following deterministic multi-physical frameworks [5,14,15,16]. ...
The strength of composite laminates can be significantly impacted by the damage caused due to lightning strikes. Quantifying such impact of lightning strikes, taking the inevitable compound influence of material and lightning current uncertainty into consideration, is of utmost importance to ensure the operational safety and serviceability in critical composite structural applications such as aircraft and wind turbines. We introduce a machine learning-enabled stochastic framework of hybrid thermal-electrical-mechanical simulations for the uncertainty quantification of residual strength post lightning strike in composite laminates. A comprehensive probabilistic analysis is presented for accurately assessing the uncertainty associated with the residual tensile strength of carbon/epoxy laminates considering stochastic temperature-dependent material properties and lightning current waveform. The results reveal that source uncertainty of the unprotected laminates significantly influences the structural strength with considerable stochastic variability. The machine learning models are exploited further for conducting global sensitivity analysis to examine the relative impact of the influencing parameters on the residual strength after lightning strikes. Seamless coupling of the Gaussian process-driven machine learning model in the finite element based multi-physical lightning strike analysis, integrating multi-stage computationally intensive simulations, leads to an efficient quantification of uncertainty for complete probabilistic characterization of the residual strength and subsequent serviceability analysis.
... 27 This phenomenon has been applicated in high-voltage transmission, lightning protection design and electronic equipment protection. Wang et al. [28][29][30] analyzed the electric fields in wind turbine under lightning strike and found that the environment conditions have an impact on the deterioration in dielectric breakdown strength of composites. Additionally, high voltage electric discharge can cause damage to composite materials, thereby reducing the safety of the structure. ...
... The material absorbs energy from the lightning arc channel and experiences a rapid temperature rise. Under elevated temperatures, polymer matrices decompose and cause fluctuations in material properties [41]. Lightning strikes commonly cause debonding because the heat generated from the lightning expands the air inside the blade, which creates internal pressure. ...
Wind turbine blades necessitate reliable field repairs. However, the effects of current wind turbine field repair surface preparation techniques were not well- documented. Poorly informed surface preparation procedures lead to poor quality repairs, so surface preparation procedure recommendations for wind turbine blade field repairs were developed. The effectiveness of current surface preparation techniques, the effects of contaminants, and alternative techniques were evaluated. Current surface preparation techniques involve using solvent wiping to remove contamination. Results indicated that solvent wiping does not significantly affect bond strengths, but solvents can gel resin surfaces. Measuring the changes in bond strengths due to contamination from composite dust and hydraulic oil with time indicated that contamination diffusion effects along bond lines were negligible, but that composite dust and hydraulic oil diminished bond strengths. Contaminants should thus be removed from bond line surfaces prior to repairs. The goal of considering alternative techniques was to increase and equalize the surface energy of repair surfaces using plasma or sizing. There were significant drops in contact angles on composite surfaces treated with plasma, so plasma treatments should continue to be considered for composite surface preparation methods. To examine sizing effects, sizing was applied to scarfed surfaces and specimens were tested in tension. Applying sizing to tapered surfaces prior to scarf repairs did not affect scarf tension ultimate stress values, failure modes, or failure surface elemental composition. In addition, there was a stiffness reduction in the scarfed specimens compared to unscarfed specimens, indicating that the scarf tension repair did not fully restore the composite plate's original properties. Scarf tension experiments were simulated using finite element analysis and results had good agreement between the experiments and the model. The surface preparation recommendation is to test whichever surface preparation methods and adhesive-substrate combinations are used for a repair prior to implementation in the field. Implementing testing of surface preparation methods with adhesive-substrate combinations into surface preparation procedures will decrease lifetime costs and increase energy production for wind turbines, which will ultimately reduce reliance on fossil fuels for societal energy needs.
... For the case of lightning impact, this structural damage is a result of complex interactions between several multi-physical mechanisms, such as thermal effects due to Joule heating, the generation of a plasma channel, transient mechanical forces due to magnetic volume forces, shock waves from the supersonic expansion of the hot plasma channel and shock waves caused by exploding material [8,9]. In order to understand these complex phenomena in more detail, several experimental studies have been performed [10][11][12][13][14]. Typically, this involves the generation of an artificial lightning strike as defined in SAE ARP5412B [15]. ...
In this manuscript, Current Component A lightning strike tests on three different types of carbon fiber reinforced composite panels are analyzed. The panels feature different levels of lightning strike protection: no protection, medium protection and heavy protection. In particular it was analyzed if there were any direct correlations between the peak electric current of the artificial lighting strike and the recorded velocities at the back surface of the composite panels. The existence of a master curve correlating the peak electric current, the mass of the composite panels and the measured back surface velocity was demonstrated. This finding implies that the back surface velocity correlates linearly to the inertia of the panel and the peak current of the lightning strike.
... Since the polarity of multiple strokes in this accident is negative, OGW is taken as the anode for calculation in this paper. In this situation, an anodic heat transfer model (as shown in Eq. (1)) is used to calculate the loaded heat flux [25][26][27][28]. q anode = q e + q u + q w (1) Where, q e is the electrons enthalpy flux caused by the increase of kinetic energy, q u is the additional heat flux caused by the acceleration of electrons under the anodic voltage drop, and q w is the heat flux generated by electrons entering the electrode surface to release work function. ...
Acquisition and analysis of the thermal damage and injected energy data of the natural lightning strikes are conducive to understand the lightning-induced damage mechanism of OGW (Overhead Ground Wire) as well as guide the improvement of the lightning simulation experimental methods in the laboratory. In this paper, a rupture accident of OGW in the power grid, which was taken as a natural lightning strike damage experiment, was used to compare the thermal damage and the injected energy with the existing common Joule heat & arc heat transfer model. The results indicated that the thermal damage of the common model is milder than that of natural lighting strike. In this accident, at least more than 45% of the injected natural lightning energy was not sourced when adopting the existing common model to simulate the thermal damage of OGW, even after considering the electrons enthalpy flux that is usually neglected in calculation.
... As a result, longitudinal Young Modulus and standard deviation of new deigned composite can be accurately obtained using numerical solutions. Moreover, the thickness imperfection to achieve the desired mechanical properties of composite parts under special conditions of loads and working can be accurately calculated by using numerical methods [76]. ...
Composite materials are used to produce multi-objective structures such as fluid reservoirs, transmission pipes, heat exchangers, pressure vessels due to high strength and stiffness to density ratios and improved corrosion resistance. The mathematical concepts can be used to simulate and analyze the generated mechanical and thermal properties of composite materials regarding to the desired performances in actual working conditions. To solve and obtain the exact solution of the developed nonlinear differential equations in the composite materials, analytical methods can be applied. Mechanical and thermal analysis of complex composite structures can be numerically analyzed using the Finite Element Method (FEM) to increase performances of composite structures in different working conditions. To decrease failure rate and increase performances of composite structures under complex loading system, thermal stress and effects of static and dynamic loads on the designed shapes of composite structures can be analytically investigated. The stresses and deformation of the composite materials under the complex applied loads can be calculated by using the FEM method in order to be used in terms of safety enhancement of composite structures. To increase the safety level as well as performances of the composite structures in different working conditions, crack development in elastic composites can be simulated and analyzed. To develop and optimize the process of composite deigning in terms of mechanical as well as thermal properties under different mechanical and thermal loading conditions, the advanced machine learning systems can be applied. A review in recent development of composite materials and structures is presented in the study and future research works are also suggested. Thus, to increase performances of composite materials and structures under complex loading systems, advanced methodology of composite designing and modification procedures can be provided by reviewing and assessing recent achievements in the published papers.
... Physical Properties of CFRP and Existing Space Materials[14][15] ...
The components of the space payload are designed using materials with high stiffness and lower weight. These parts ought to be able to withstand the harsh climatic conditions over their entire life cycle without failing. Future space missions require lightweight materials with great thermal and electrical and mechanical strength. Carbon fiber reinforced polymer (CFRP), which is frequently utilized for space payload components, offers significant bulk savings and excellent strength. Carbon Nanotubes (CNTs) effectively increase both thermal and electrical conductivity. The CNTs must satisfy the requirement of being disseminated by the method of Solution Mixing for being considered as an efficient reinforcement to achieve high conductivity and strength of polymer composites. CNT nanocomposites and their quality is generally influenced by the type of CNTs, their purity, loading amount, aspect ratio, interfacial bonding between the polymer and nanotube, and alignment. A successful application of the processing techniques acts as a key parameter for the enactment of the CNT-CFRP composite. This review article aids in the process parameter optimization for the production of space payload components, which are needed to replace the current high-density space-qualified materials. This study summarizes the synthesis techniques, physical properties, and space applications of CNT-reinforced composite and FGM. These documents could serve as a ready reference for future researchers and relevant industries. Abstract: The components of the space payload are designed using materials with high stiffness and lower weight. These parts ought to be able to withstand the harsh climatic conditions over their entire life cycle without failing. Future space missions require lightweight materials with great thermal and electrical and mechanical strength. Carbon fiber reinforced polymer (CFRP), which is frequently utilized for space payload components, offers significant bulk savings and excellent strength. Carbon Nanotubes (CNTs) effectively increase both thermal and electrical conductivity. The CNTs must satisfy the requirement of being disseminated by the method of Solution Mixing for being considered as an efficient reinforcement to achieve high conductivity and strength of polymer composites. CNT nanocomposites and their quality is generally influenced by the type of CNTs, their purity, loading amount, aspect ratio, interfacial bonding between the polymer and nanotube, and alignment. A successful application of the processing techniques acts as a key parameter for the enactment of the CNT-CFRP composite. This review article aids in the process parameter optimization for the production of space payload components, which are needed to replace the current high-density space-qualified materials. This study summarizes the synthesis techniques, physical properties, and space applications of CNT-reinforced composite and FGM. These documents could serve as a ready reference for future researchers and relevant industries.
... However, due to preparation difficulty in large size and the high processing cost, the above studies have significant limitations in application. With studying the lightning strike behavior of CFRP composites through experiments [19,20] and simulations [21][22][23][24][25], the main damage mechanism has been proposed as thermal ablation and mechanical fracture. The experimental and numerical studies indicate that component A leads to the most serious damage [26], whereas there is no material that can withstand a Component A lightning strike for 200 kA reported. ...
... The amount and the time-scales of the different factors, e.g., mechanical loads or stresses, temperature, humidity, etc., vary significantly. In aerospace applications of FRP composites, there are additional factors that may further contribute to degradation of the material properties, including their delamination resistance, e.g., particle impact, electromagnetic radiation or lightning [91][92][93][94]. ...
Quasi-static or cyclic loading of an artificial starter crack in unidirectionally fibre-reinforced composite test coupons yields fracture mechanics data—the toughness or strain-energy release rate (labelled G)—for characterising delamination initiation and propagation. Thus far, the reproducibility of these tests is typically between 10 and 20%. However, differences in the size and possibly the shape, but also in the fibre lay-up, between test coupons and components or structures raise additional questions: Is G from a coupon test a suitable parameter for describing the behaviour of delaminations in composite structures? Can planar, two-dimensional, delamination propagation in composite plates or shells be properly predicted from essentially one-dimensional propagation in coupons? How does fibre bridging in unidirectionally reinforced test coupons relate to delamination propagation in multidirectional lay-ups of components and structures? How can multiple, localised delaminations—often created by impact in composite structures—and their interaction under service loads with constant or variable amplitudes be accounted for? Does planar delamination propagation depend on laminate thickness, thickness variation or the overall shape of the structure? How does exposure to different, variable service environments affect delamination initiation and propagation? Is the microscopic and mesoscopic morphology of FRP composite structures sufficiently understood for accurate predictive modelling and simulation of delamination behaviour? This contribution will examine selected issues and discuss the consequences for test development and analysis. The discussion indicates that current coupon testing and analysis are unlikely to provide the data for reliable long-term predictions of delamination behaviour in FRP composite structures. The attempts to make the building block design methodology for composite structures more efficient via combinations of experiments and related modelling look promising, but models require input data with low scatter and, even more importantly, insight into the physics of the microscopic damage processes yielding delamination initiation and propagation.
... Carbon Fibre Reinforced Polymer (CFRP) is one of the most desirable materials for space industries due to its high specific stiffness. It is 30% more strong, but five times less in weight compare to traditional space material like Kovar & Invar as shown in Table 1 (Wang 2017;Davis 2000). For the interplanetary missions where the mass is critical factor of design criteria, CFRP is most advantageous. ...
... Carbon Fibre Reinforced Polymer (CFRP) is one of the most desirable materials for space industries due to its high specific stiffness. It is 30% more strong, but five times less in weight compare to traditional space material like Kovar & Invar as shown in Table 1 (Wang 2017;Davis 2000). For the interplanetary missions where the mass is critical factor of design criteria, CFRP is most advantageous. ...
The high specific stiffness materials are used to design the space payload components. These components should sustain the extreme environmental condition throughout their life cycle without failure. The prerequisites of future space missions need lightweight materials which must be mechanically strong and high thermal and electrically conductive. The Carbon Nanotubes (CNTs) are efficient filler material in composite or metal matrix to enhance greater electrical and thermal conductivity. The quality of the CNT nano composite relies upon several parameters like the types of CNTs, its purity, aspect ratio, amount of loading, alignment, and interfacial adhesion between the nanotube and polymer. The performance of the CNT-CFRP composite depends on the successful execution of the processing technique. This review paper intends to highlight the enhancement of the mechanical, thermal, electrical properties of the composite, and the challenges to achieving it. This review paper helps to optimise the process parameters to fabricate Space Payload Components, required to replace existing high-density Space Qualified Materials. This review paper should help optimize the process parameters to fabricate Space Payload Components, which can be excellent alternatives to the existing high-density Space Qualified Materials without making any compromise on the performance index.
... In parallel, computational investigation to predict the damage induced by lightning on aeronautical protection layers -considering a model of stationary arc in a first approachare developed. Ogasawara et al. (2010), Chemartin et al. (2012), Abdelal and Murphy (2014) and Wang (2017) used Finite Element Methods (FEM) to consider the effects of a multi-physics damage couplingelectric-thermal-mechanical-chemical to carbon/glass reinforced composite. These simulation advances are coupled with the MHD model to investigate the damage of the spcific swept-stroke phenomenon in Ma et al. (2020) and thus predict the enlarged thermal damages due to aerodynamic flow. ...
In the domain of aeronautical industry, the risk of lightning strike is taken into account from the conception of the aircrafts as the phenomenon statistically occurs every 1000 to 10000 flight hours. As this phenomenon involves a lightning channel that is static in the terrestrial reference frame and an aircraft that can reach a speed of 100 m/s in the take-off or in the landing phase, there is a displacement of the impact area – the arc root - on the aircraft outer skin. This phenomenon is referred to as swept-stroke phenomenon. Thus, all the parts of the aircraft are exposed to the risk of direct electric and thermomechanical damages induced by the lightning strikes. Therefore, it is necessary to understand the physical mechanisms that drive the displacement of the arc root to optimize lightning strike protections. There is a significant bibliography about the modelling of this displacement combining electromagnetism and fluid mechanics equations. Though, the existing simulation codes still have not been validated by the implementation of an experimental aircraft simulation that would be struck down by lightning to create a reference database for the physical parameters of the phenomenon. This PhD thesis aims to reproduce such an experiment and to establish such a reference database.
To reproduce a representative experiment of swept-stroke, a high power electric generator with a Buck configuration and capable to reproduce an electric arc respecting the aeronautical standard lightning waveform is designed, implemented and tested. Electric arcs of a few kV representative of the continuous lightning waveform standard are created and elongated until 1.50 m. The propulsion of test samples to speeds of several tens m/s is realized with the design, development and implementation of an Railgun electromagnetic launcher: a supercapacitor bank enables the injection of a current of 25 kA during 50 ms into a Laplace’s rails system and so to propel samples of a few hundred grams to the desired speeds within 2 m of acceleration. The coupling of the electric generator and the Railgun enables the reproduction and the study of the swept-stroke: electrical measures and optic diagnostics through high speed camera and spectroscopy are implemented to characterize the electric, hydrodynamic and thermal behavior of the moving electric arc. The impact point displacement is also characterized and analyzed. These measures and analyses are also conducted with a Wind tunnel that provokes the displacement of the electric arc on the test sample, replacing the Railgun. From this study, the comparison between the two modes of relative motion between the electric arc and the test sample is established.
... During the service of wind turbine blades, cracks, fracture, fiber spalling, surface abrasion, local debonding, and skin collapse are prone to occur [12][13][14]. The cracks are often the main damage form. ...
The development of wind power industry is one of the important ways to solve current energy shortage and reduce carbon emissions. As the key component to capture wind energy, fiber-reinforced composite (FRC) wind turbine blades are subject to complex alternating loads in harsh environments. It is easy to produce various damages during long-term service, such as cracks, fiber spalling, and surface abrasion. Among them, crack is the most serious damage. FRC is a kind of composite material with obvious anisotropy, which is very sensitive to crack damage. The generation and propagation of cracks can easily lead to further failure of the whole blade, resulting in great economic losses and safety risks. How to deal with the damage of wind turbine blades in time has become a thorny problem in the wind power industry. In this paper, the current research status of the crack damage for the FRC wind turbine blade is comprehensively reviewed from the formation mechanism of crack and the detection and evaluation methods as well as the repair technologies. Finally, the development of related technologies has been prospected.
... The lightning strike damage mechanisms of CFRP composites are widely studied in the literature [43][44][45][46][47][48][49]. To briefly mention, the extremely high lightning current resulted in a rapid temperature rise in the composite specimens (up to 3316 °C) and lead to the decomposition of epoxy resin. ...
Conductive nanofillers, such as carbon nanotube, graphene nanoplatelets, and carbon black particles (with diameters in nanometers) have been shown to enhance the electrical conductivity of fiber reinforced polymer matrix composites in many existing studies. The motivation is primarily for lightning strike protection, electromagnetic interference shielding, de-icing, and the manufacturing of lightweight electronic components. In this paper, we evaluate the lightning strike damage tolerance of carbon fiber reinforced polymer (CFRP) matrix composite laminates containing conductive nanofillers with varying weight fractions, including carbon black (CB), carbon nanotubes (CNT), and a mix of CB and CNT, through simulated lightning strike tests, followed by both non-destructive ultrasonic inspection and destructive sectioning to characterize the damage inflicted by the simulated lightning strike. Three-point flexural tests are performed to evaluate the residual strength retained by all CFRP specimens. Results show that lightning strike damage experienced varying levels of reduction for CFRP composite specimens containing conductive fillers in comparison to the baseline specimen without fillers. Notably, the delamination only penetrated to the interface between the 1st and 2nd layer for the specimen with 0.25 wt.% CNT in comparison to the baseline CFRP specimen for which the delamination penetrated to the interface between the 5th and 6th layer. Moreover, the retention of the flexural modulus increased from 26.5% to a maximum of 95.0% for the specimen with 0.25 wt.% hybrid CB and CNT. Yet, we show that using our chosen conductive fillers cannot fully eliminate lightning strike damage. Additionally, adding conductive fillers could compromise the flexural properties. We provide discussions on future recommendations on using conductive fillers for the lightning strike protection of CFRP composites.
... The current conduction follows Ohm's law [23]. ...
Glass fiber-reinforced polymer materials have been effectively used in civil aviation aircraft, but due to low electrical conductivity, a large area of ablation damage will occur after lightning strikes, which greatly threatens the safety of civil aircrafts. Based on this, the coupled electrical-thermal finite element analysis model for a lightning ablation damage of glass fiber reinforced polymer materials is established, and the analysis results are compared with the experiment, and the error rate is 1.26%, which verifies the accuracy of the model. In addition, different influencing factors are analyzed to study the lightning protection characteristics of glass fiber reinforced polymer on carbon fiber-reinforced polymer laminates. The results show that glass fiber reinforced polymer materials have low lightning resistance, but they can effectively reduce the lightning ablation damage area of carbon fiber reinforced polymer laminates under the joint protection of them and aluminum coating. However, they have different protective effects on different protective forms of laminates. Among them, the thickness of aluminum coating has a higher impact on the lightning protection efficiency of full spraying aluminum protective laminates, and the thickness of glass fiber reinforced polymer materials has a higher impact on the lightning protection efficiency of local spraying aluminum protective laminates.
... IGHTNING is one of the major natural causes of damages to structures on earth, and these damages come with associated economic consequences [1][2][3]. Lightning hazards can be in different forms, such as thermal and mechanical damages, insulation failures, lightning-induced fires, electromagnetic compatibility issues, touch and step voltages, death of animals and humans in extreme cases etc. A number of lightning-related disasters such as plane crashes, disruption of power grids and supply outages [4], space rocket launch failures, e.g. ...
In this data era, data mining and machine learning, in general, have been applied in various research fields. Designing adequate lightning protection systems requires a good understanding of how lightning interacts with grounded structures. The probability of a lightning strike to various points on a structure reflects the associated likelihood for a lightning strike to terminate on such points. In this study, the dataset generated by applying a numerical approach to the computation of the dynamic electro-geometrical model for a cuboid structure was analyzed using data mining techniques. Data classification and regression-based predictive analyses were carried out on the Orange data-mining platform and MATLAB. Cases with 100% classification accuracy were observed using the Random Forest and the AdaBoost algorithms.
... The thermal effect of the return stroke current is believed to be the cause of puncture damage to wind turbine blades [6,7]. To investigate lightning thermal damage to wind blades, many researchers have carried out impulse current tests on blades and laminates made of GFRP and carbon fibre reinforced polymer (CFRP) [8]. ...
The puncture of glass fibre reinforced polymer (GFRP) laminate is a primary damage pattern of wind turbine blades due to lightning strikes. A numerical simulation model of positive streamer propagation in a needle‐to‐plate air gap with a GFRP laminate is established to investigate the breakdown mechanism of GFRP laminate. The model not only considers the dynamics of charged particles in the air and the composite laminate, but also the current continuity at gas–solid interfaces. The simulated streamer discharge pattern and the surface streamer length are in good agreement with the observation results. The distributions and evolutions of the electron number density, electric field, and surface charge densities during streamer propagation are obtained. It is found that the enhancement of the electric field on the GFRP laminate is caused by the rapid deposition of positive and negative space charges on the GFRP laminate after a secondary streamer incepts on the lower surface of the GFRP laminate. The effects of the applied voltage, relative permittivity, and thickness of the GFRP laminate on the electric field on the GFRP laminate are investigated. The obtained results could assist in further understanding of the mechanism of GFRP wind blade breakdown due to lightning strikes.
... Design formulation for any product by considering all parameters may be regarded as an intermediate stage that bridges the gap between two processes. This is preceded by material selection based on desired quality, economy and quantity; and followed by development of product for the desired application with a well-defined design and preselected material, which is obviously a complex task for the manufacturer [86]. All parameters have to be measured appropriately to define the desired design, although nowadays many computational tools are available for design and analysis and FEM is the most preferred one [25]. ...
Introduction
Biodegradable materials have been at the forefront of cutting-edge research and offer a truly viable option in designing and manufacturing of bone implants in biomedical engineering. Most research regarding these materials has focused on their biological characteristics and mechanical behaviour vis-à-vis non-biodegradable (NB) materials; but the design aspects and parametric configurations of biodegradable bone implant have somehow not received as much attention as they deserved.
Area Covered
This review aims to develop insight into parametrically conceptualized design of biodegradable bone implant and takes into due consideration the characteristics of bone-biodegradable implant interface (BBII), design techniques employed for conventionally-used bone implants to optimize parameters using standard test methods, traditional design, and finite element analysis approaches for implant and healing behaviour, manufacturing techniques, real–time surgical simulations, etc.
Expert Opinion
Some successful and conventionally used NB bone implants do not dissolve or degrade with time and require removal through a complicated surgery after fulfilling the intended objectives. These bone implants should be reconceptualised and designed with an appropriate biodegradable material while paying due attention to all factors/parameters involved and striking a balance between these factors with the ultimate objective of fulfilling all desired orthopaedic requirements.
... Where A, Ea, R, and n are the coefficient of the decomposing rate, the activation energy, universal gas constant, and the reaction order, respectively; ρ, ρv and ρc are the density, density at the virgin state, and density at the charred state, respectively. A, Ea, R, and n of the above equation Decomposition of the polymer matrix can be found from the thermogravimetric analysis [13,36]. ...
Wind turbines and aircraft are generally made of less conductive carbon/glass composites.
Significant damages may occur to these materials if they are struck by high energy lightning strikes.
Damage and structural response of composites is essentially a multiphysics domain, involving thermal,
electrical, magnetic and structural analysis. In this article, the fundamental physics of lightning,
multiphysics analysis, numerical implementation and experimental studies about composite materials
are reviewed. The relevant international standards and possible characterization methods of lightning
strike damage are also reproduced in this article. In addition to this, the current and prospective
technologies, to protect composite from lightning strikes are also provided
... The above direct effects associated with the interaction of lightning on CFRP materials are shown in Figure 2.24. The application of current through the channel is initially small and gradually grows [34], [94] as indicated by the different colour channels in Figure 2.24, which increase with the time increments (t1, t2, and t3) and changes the application of current density on the surface. The channel is restricted by the paint, which results in dielectric breakdown [34], [89]. ...
To meet worldwide increases in energy demand Wind Turbine (WT) manufacturers are producing longer blades to generate more energy. These blades contain Carbon Fibre Reinforced Polymers (CFRP) in the load carrying structures to lightweight the blade. The introduction of the CFRP composites has presented new challenges in protecting the structure from lightning. The semiconductive nature of CFRP leads to an additional path to ground for the current in the structure and the anisotropic nature of the material’s thermal and electrical properties leads to large amounts of resistive heating especially in the through-thickness direction where the electrical conductivity is the lowest. The aim of this PhD is to devise a new means of assessing the damage and resulting structural behaviour caused by a lightning strike. A modelling framework is developed and validated against high fidelity experimental data that can be used by design engineers to understand the consequences of various lightning damage scenarios and the effectiveness of lightning protection methods. The framework is validated against a representative scale WT sparcap test component in the form of a large panel subjected to compression.
The novel damage model is a thermal-electrical Joule heating model which simulates the resistive heating in a UD laminate with electric field dependent material properties to account for electric breakdown. The damage prediction is then exported into a structural Finite Element Model (FEM) by assuming the damaged elements have different material properties. The structural behaviour under compression loading is the main design driver for long slender WT blades. Therefore, the structural model simulates the behaviour of a damaged laminate in a non-linear post-buckling FEM. To validate and inform the damage model and the FEM two different types of tests were conducted.
The first type of test simulated the lightning strikes and comprised of direct strike and conducted current tests. The effect of conducting current along the fibre direction showed a deleterious effect on the compressive and shear properties of the material. Initial direct strike tests were used to vary the typical lightning parameters to determine the largest influence on damage among peak current, specific energy, or charge. The last direct strike test is conducted on a representative WT sparcap panel. All damaged panels were evaluated using visual inspection, a new thermography technique, and X-ray computed tomography (CT). The newly developed damage model was validated using the experimental observations with the damage area predictions within 15% of the visual observation and the damage depth within 5% of the CT scans. Hence, the electric field dependency was successfully implemented in the model.
The second test type was a structural test that incorporated the development of a new testing methodology named the compression after lightning strike (CALS) test. Large representative sparcap panel specimens, with and without lightning damage were tested to failure in the CALS rig and Digital Image Correlation (DIC) was used to determine the resulting surface displacements and strains. The structural model closely predicted the compressive behaviour and failure loads identified by the DIC. The resulting structural model calculated the first ply failure stresses from the LaRC failure criteria which were within 8% of experimental values, which provided a successful validation of the modelling framework.
... 2．There is no secondary cracking of the pyrolysis gas. For one-dimensional ablation problem, the in-depth heat conduction equation that considers both material decomposition and surface ablation [34][35][36][37][38] can be expressed as ...
Thermal ablation plays an important role in the aerospace field. In this paper, to study the chemical kinetics effects on heat transfer and surface ablation of the charring ablative material during aerodynamic heating, a charring ablation model was established using the finite element method. AVCOAT5026-39H/CG material, one typical thermal protection material used in thermal protection system, was employed as the ablative material and heated by aerodynamic heating condition experienced by Apollo 4. The finite element model considers the decomposition of the resin within the charring material and the removal of the surface material, and uses Darcy?s law to simulate the fluid flow in the porous char. Results showed that the model can be used for the ablation analysis of charring materials. Then effects of chemical kinetics on ablation were discussed in terms of four aspects, including temperature, surface recession, density distribution, and mass flux of pyrolysis gas. The pre-exponential factor and activation energy have different effects on ablation, while the effect of the reaction order is little. This paper is helpful to understand the heating and ablation process of charring ablative materials and to provide technical references for the selection and design of thermal protection materials.
div>Modern aircraft, ships, and offshore structures are increasingly constructed using fiber-reinforced composite materials. However, when subjected to lightning strikes, these materials can suffer significant structural and functional damage due to their electrical and thermal properties. This study aims to develop a novel finite element (FE) model to minimize the error in estimating the thermal damage caused during lightning strikes. This will aid in design and optimization of lightning protection systems. The developed model introduces a simplified numerical approach to model the lightning arc interaction with CFRP laminate. The existing FE model includes idealized loading conditions, leading to high error in estimation of severe damage area and in-depth damage. The proposed methodology incorporates a more realistic lightning-induced loading pattern to improve accuracy. Several cases are analyzed using available FE methods and compared to the proposed model (case 6) to evaluate the extent of damage. The thermal damage results are validated against baseline experimental data, demonstrating that the proposed FE model reduces the error from over 40% (observed in rest of the cases representing existing FE approaches) to within 10%.</div
The tufting technology has the advantages of high flexibility and high economy. Research has found that metal tufting structures can significantly improve the mechanical and electrical properties of carbon fiber composites, and have great prospects in engineering applications. In order to investigate the damage characteristics of carbon fiber CFRP laminates with metal tufted structures during lightning strikes and the influence of structural parameters on lightning protection effectiveness, an electric thermal coupling model of CFRP laminates with metal tufted structures was established. Comparing the simulation and experimental results under the same load condition, it was found that the two were consistent in terms of damage appearance, damage area, and damage propagation trend, proving the effectiveness of the model. The transverse heat transfer process and current conduction path of CFRP laminates with metal cluster structure were discussed. The research results indicate that the ablation surface area of CFRP laminates with metal tufted structures is reduced to 8.06% of the reference component. Wire spacing had an effect on the area and shape of the area of the high potential region, and the wire spacing had the greatest impact on the ablation area of lightning strikes.
Offshore structures and airframes are more likely to catch lightning. Carbon/glass Fibre Reinforced Polymer (FRP) composites are the top priority material for such structures, for their ability to provide superior strength and stiffness at low weight cost. However, CFRP exhibits high resistivity and anisotropy, producing extensive thermal damage morphology after a lightning strike event. The previous review studies are focussed on the statistics of lightning events, conditions favouring the lightning strikes, and the effect of lightning waveform parameters onto damage. However, a detailed discussion on the experimental findings for lightning arc column interaction and damage imposed on CFRP is not available. Herein, the literature on experimental investigations compiled together to discuss the author’s assessment comparing the damage morphology. Also, this review article presents a holistic view of arc column energetics, its interaction behaviour with structures composed of CFRP and the characterisation of the lightning damage profile onto such structures. Furthermore, this review paper compares the available numerical modelling techniques and discussed their merits and strength in predicting the different aspects of damage morphology.
Carbon fiber reinforced polymer composites (CFRPC) are being used as primary structures in many applications. However, unlike metallic materials, they are susceptible to damage by lightning strikes. When lightning strikes, due to its poor electrical conductivity, the composite material generates localized resistive heating near the strike area. This resistive heat causes elevated temperatures near the strike area, which leads to material property changes and the structural material's stiffness and strength reduction. As part of this study, a finite element (FE)-based coupled electro-thermo-mechanical modeling approach was adopted to simulate the effect of lightning strikes on a unidirectional (UD) carbon fiber reinforced polymer composite model to predict the residual compressive strength of the material. In the current study, a two-dimensional (2D), micromechanical finite element model of CFRPC was used to quantify its residual compressive response when subjected to simulated lightning strikes with different peak currents using the software ABAQUS. The normalized residual compressive strengths for various peak currents obtained from the proposed electro-thermo-mechanical model were compared with the available experimental data from the literature. The effectiveness of an electrically conductive protective coating in minimizing the compressive strength reduction was also evaluated. Further, the optimum electrical conductivity of the coating in terms of the matrix conductivity, for maintaining the desired compressive strength was also estimated. Furthermore, the effect of change in thickness of the conductive coating in compressive strength change was evaluated by considering two different coating thicknesses. The results show that for a given peak current, the thinner coating will not compromise the compressive strength as long as the conductance of the thin and thick coating is the same.
This study proposes a coupled thermal-chemical numerical model for preventing the thermal degradation of carbon fibre (CF) reinforced polymers at extreme heating rates. Its applicability is demonstrated in a laser-heating case study of CF-reinforced poly-ether-ether-ketone (CF/PEEK). The kinetic parameters of the PEEK matrix, derived from thermogravimetric analysis at conventional heating rates, are introduced in the model and an extrapolation approach is applied to investigate the laser heating of CF/PEEK. The results show that the model captures the heating rate effect on the decomposition of the material, and is used to identify the processing conditions that can reach high temperatures without triggering the thermal degradation mechanisms of the PEEK matrix. Then, a multi-technique experimental investigation takes place to identify the processing conditions that first trigger the thermal degradation mechanisms of CF/PEEK in the examined laser-heating case study. Interestingly, a good agreement is found between the experimental and numerical investigations which validates the model and the applied extrapolation approach.
Composite materials have been widely used in civil aviation aircraft, but a large area of ablation damage occurs after lightning strikes, which threatens the operation safety of civil aviation aircraft. The composite material is fixed by multiple fasteners. The different installation positions of fasteners have a great influence on the result of lightning damage of composite. Based on these, a lightning ablation damage model of laminates with multiple fasteners is established, and the accuracy of the model is verified by comparing with the results in the references. In addition, the effect of different installation methods of multiple fasteners on the lightning ablation damage of laminates is studied. The results show that the number of fasteners is not the decisive factor among the factors that affect the ablation damage of laminates with multiple fasteners, and the installation layout of fasteners has an important impact on the damage results. When the fiber direction and aspect ratio of the laminate are the same, the maximum ablation damage area of terrible fasteners layout is 1.27 times the minimum ablation damage area of best fasteners layout under the action of lightning peak current of 200 kA.
Electro-thermal damage mechanisms on direct current are important for the reliability design of carbon fiber reinforced composites in an electric environment. Here we studied the effect of direct current direction on the electro-thermal damage of carbon fiber/epoxy plain woven laminates. The current was applied on the composite along longitudinal/through-thickness directions. We used an infrared camera to record temperature distribution from Joule heat on the composite surface. The surface temperature distribution under the through-thickness current was more nonuniform than that under the longitudinal current. We conducted three-point bending and micro-CT tests to reveal the effect of direct current treatment on mechanical behavior. We found that the through-thickness current reduced the composite flexural performance, while the longitudinal current did not. The through-thickness current induced the electro-thermal damage in the composites but without crack defect. Interfacial degradation is a new electro-thermal damage mode.
Wind turbines and aircraft are generally made of less conductive carbon/glass composites. Significant damages may occur to these materials if they are struck by high energy lightning strikes. Damage and structural response of composites is essentially a multiphysics domain, involving thermal, electrical, magnetic and structural analysis. In this article, the fundamental physics of lightning, multiphysics analysis, numerical implementation and experimental studies about composite materials are reviewed. The relevant international standards and possible characterization methods of lightning strike damage are also reproduced in this article. In addition to this, the current and prospective technologies, to protect composite from lightning strikes are also provided.
This paper presents a novel numerical approach to simulate lightning strike damage to equipotential bonding interfaces of wind turbine blades, and model validation based on high-current testing. Modern rotor blades are equipped with metal receptors to intercept the lightning leader and metal down conductors to conduct the lightning current, preventing the direct attachment to the CFRP spars. In such conditions, damage in the form of resin thermal degradation and sparks develop inside the blade at the equipotential bonding interfaces. Excellent correlation was found between the numerical predictions and test results in terms of current and temperature distributions. High temperatures were predicted at the sparking areas observed in the tests, which suggested that the damage is thermally activated. Thermogravimetric analysis data indicated that the epoxy pyrolysis process evolves in stages, and that sparking events are often initiated by release of gases and formation of small voids at temperatures lower than expected.
Lightning strike simulations have used decomposition models, derived from TGA experiments, to model material behaviour at elevated heating rates and temperatures. Such experiments, conducted non-isothermally and at low heating rates, are extrapolated to conditions assumed during a lightning strike event. However, no experiments have been carried out in the literature to verify and understand the impact of the extrapolation assumptions. This work seeks to understand the influence of the approach used to adjust material properties to reflect heating rates present during a lightning strike, which cannot be achieved in the TGA experiments. A combination of experimental and simulations studies was undertaken, including prediction sensitivity analysis through simulation, experiments conducted at a variety of heating rates, thermokinetic modelling to extrapolate data, and finally further thermal-electric models to demonstrate the effect of predicted heating rate on thermal damage. It is demonstrated that the extrapolation approach for heating rate can impact thermal damage predictions. For the studied lightning strike tests and using a maximum heating rate extrapolation (20,000 oC/min), herein damage predictions are improved, reducing the error in predicted severe damage area to within 8% of the experimental values.
A primary motivation for this study comes from the need to improve the ability of polymer matrix composites to withstand lightning strikes. In particular, we are concerned with lightning strike damage in composite wind turbine blades. The problem is essentially multiphysic, as the electric-current-induced temperature in the composite blade subjected to a lightning strike may reach up to 1,200 °C, leading to extensive thermal damage including surface damage, delamination, cracks, matrix decomposition, fiber breakage and sublimation, and abrupt failure of the blade. In this work, the thermal response of the polymer-matrix composite laminate used in a Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00) subjected to lightning strike is studied. The tip region composite panel is considered, as it has been reported in the literature that the blade tip is more susceptible to lightning strike than the remaining parts of the blade. A physical model to show the surface interaction between the lightning arc and the composite structure has been developed. The model provides time-and electric-current-dependent variation of the lightning arc radius and lightning-current-induced heat flux generated at the composite surface. The temperature-dependent thermal properties of the VectorPly E-LT 5500 unidirectional [0]2 E-glass fiber vinyl ester resin matrix fabric and SNL triaxial [±45]2[0]2 E-glass fiber vinyl ester resin matrix fabric used in the wind blade tip composite panel were derived using available experimental data. The formulated nonlinear transient heat transfer problem with moving boundary is solved using the finite element method. The solution procedure accounts for phase transitions in the materials, and the obtained results include temperature field profiles and evolution of the thermal damage.
Receptor plays an essential role in determining the efficiency of lightning strike protection (LSP) on wind turbine blades. To investigate the effects of receptors with different shapes and sizes on the LSP, we apply five different receptor configurations to the blade of a high-fidelity wind turbine model. The static electric field strength on the blade surfaces due to a lightning stepped leader is predicted through the development of a numerical model with finite element analysis. The interception efficiency is evaluated by comparing the predicted maximum electric field strength in the vicinity of the receptors. In addition, the locations of the predicted lightning strike attachment points match well with those obtained by experimental measurements, which validate the current numerical approach.
According to the mathematical analysis model constructed on the basis of energy-balance relationship in lightning strike, and accompany with the simplified calculation strategy of composite resin pyrolysis degree dependent electrical conductivity, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate suffered from lightning current was established based on ABAQUS, to elucidate the effects of lighting current waveform parameters and thermal/electrical properties of composite laminate on the extent of ablation damage. Simulated predictions agree well with the composite lightning strike directed effect experimental data, illustrating the potential accuracy of the constructed model. The analytical results revealed that extent of composite lightning strike ablation damage can be characterized by action integral validly, there exist remarkable power function relationships between action integral and visual damage area, projected damage area, maximum damage depth and damage volume of ablation damage, and enhancing the electrical conductivity and specific heat of composite, ablation damage will be descended obviously, power function relationships also exist between electrical conductivity, specific heat and ablation damage, however, the impact of thermal conductivity on the extent of ablation damage is not notable. The conclusions obtained provide some guidance for composite anti-lightning strike structure-function integration design.
In this paper, the electric fields in the wind turbine blades due to the lightning stepped leader are studied, and the dielectric breakdown is assessed. The developed finite element analysis (FEA) includes the full length of the leader and enables one to incorporate various uniform and non-uniform charge density models. The lightning striking distance is calculated using the rolling sphere method. The electric field in a horizontal axis wind turbine with three blades representing Sandia 100 m All-glass Baseline Wind Turbine Blades (SNL 100-00) at three different lightning protection levels (LPL) is computed and compared to the dielectric breakdown strength of the blades. The dielectric breakdown strength of the blades is evaluated based on the experimental data. The results show that the tip region of the blade is the most vulnerable to the dielectric breakdown with the safety factor as low as 1.32 at LPL I.
This work is concerned with thermal ablation modeling in carbon fiber-reinforced polymer-matrix composite laminates subjected to the lightnig strike. Both direct heat injection and Joule heating produced by the lightning current are taken into account. First, a model describing interaction of the lightning current channel with a conductive structure is presented. The model includes channel expansion and spatial and temporal distribution of the lightning current and linghtning-induced heat flux. Second, anisotropic electrical and thermal properties of the CFRP composite laminates are determined in a wide temperature range (up to the sublimation temperature of the carbon fibers) using experimental data and micromechanics considerations. Third, a nonlinear thermo-electric coupled problem is formulated and solved for a CFRP composite laminate to determine the electric-current-induced temperature distribution and associated thermal ablation. Finally, the obtained predictions of thermal ablation in the CFRP composite laminate are compared to the reported experimental results. It is found that the predicted thermal ablation depths agree well with those reported in the experimental study.
Lightning is a major cause of damage in laminated composite aerospace structures during flight. The most significant failure mode induced by lightning is delamination, which might extend well beyond the visible damage zone, and requires sophisticated techniques and equipment to detect. Therefore, it is crucial to develop a numerical tool capable of predicting the damage zone induced from a lightning strike to minimize costly repair acreage and supplement extremely expensive lightning experiments. Herein, a detailed numerical study consisting of a multidirectional composite with user-defined, temperature-dependent, interlaminar elements subjected to a lightning strike is designed, and delamination/damage expansion is studied under specified conditions. It is observed both the size and shape of the delamination zone are strongly dependent on the assumed temperature-dependent fracture toughness; the primary parameter controlling lightning-induced delamination propagation. An accurate estimation of the fracture toughness profile is crucial in order to have a reliable prediction of the delamination zone and avoid sub-critical structural failures.
This paper presents statistical data about lightning damage on wind turbine blades reported at different wind farms in the U.S. The analysis is based on 304 cases of damage due to direct lightning attachment on the blade surface. This study includes a large variety of blades with different lengths, laminate structure and lightning protection systems. The statistics comprises the distribution of the lightning damage along the blade and classifies the damage by severity. In addition, the frequency of lightning damage to more than one blade of a wind turbine after a thunderstorm is assessed. The results of the analysis show that the majority of the lightning damages are concentrated at the tip of the blade. Furthermore, all the blades involved in the study show a great similarity in the distribution of damages along the blade and the characteristics of the damages, even concerning the significant differences in the blades geometry and materials.
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.
A physics-based model describing the thermal interaction between a lightning channel and a composite structure has been developed. The model includes: (i) spatial and temporal evolution of the lightning channel as a function of the electric current waveform; (ii) temporary and spatially non-uniform heat flux generated at the composite structure, where the heat flux is an explicit function of the electric current waveform and the instant lightning channel radius; (iii) nonlinear transient heat transfer problem formulation for layered anisotropic composites that accounts for temperature-dependent material properties, a moving boundary of the expanding lightning channel, and phase transition moving boundary associated with instantaneous material removal due to sublimation. The model is applied for evaluation of thermal damage of the tip glass fiber reinforced polymer matrix composite panel of the Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00) subjected to lightning strike.
Polymer composites are widely used for high temperature thermal protection (TPS)materials for spacecraft heat shields, and nozzle liners for solid propellant rocket motors. Newly developed silicon containing polymer, abbreviated MSP (Mitsui Silicon Containing Polymer), possesses high decomposition temperature (500 C), and high char yield (>94% at 1000 C)after pyrolysis. Therefore, the MSP polymer has potential as matrix resin of high performance ablative composites compared with conventional phenolic resins. In this study, thermal performance and ablation characteristics of a carbon composite with the MSP polymer (CF/MSP) were investigated under supersonic plasma air stream. The cold wall heat fluxes ranged from 1.2 to 11.0MW/m2. Conventional carbon fiber phenolic (CF/PR) composite was tested at the similar conditions for direct comparison. The mass loss of the CF/MSP composite was far less than that of the CF/PR composite, which is due to higher char yield and consequent high density of char layer. On the other hand, higher internal temperature was measured in the CF/MSP composite.
Increasing use of composite materials in applications of aerospace and civil structures, their safety andreliability under high temperature andfire environments must be assured. This paper covers a study of structural integrity of composite structures that are exposedto fire or intense heat. The parameters that affect their critical buckling loads and the buckling strengths under these circumstances were investigated. It is shown that for a given material, increasing the ply thickness will increase the buckling strength of the laminate. It is also concluded that a symmetric lay-up of laminate exhibits a higher buckling strength than the one of an unsymmetric lay-up.
The response of Kevlar and graphite/epoxy composites subjected to simulated nuclear or laser thermal loads was measured. A solar furnace was used to radiantly heat samples at flux rates of up to 55 cal/cm²/sec and total fluences of approximately 100 cal/cm². An iterative numerical technique was used to estimate the thermophysical properties of the materials by matching observed temperature-time histories with analytical predictions. Comparison of results obtained during this program with previously published data suggests that free stream velocity, which affects smoke blockage and char layer removal, is a critical design parameter.
An analytical procedure is presented for predicting the loss in integrity of composite structures subjected to simultaneous intense heating and applied mechanical loads. An in tegral part of the method is a nonlinear, two-dimensional, finite difference thermal analysis which considers the effects of surface ablation, re-irradiation losses, and temperature-dependent thermophysical properties. Another important feature of the structural survivability model is a flat-plate finite element code, based on the Mindlin theory, which is coupled to a maximum stress failure criterion. Predictions from the analysis methodology are compared with experimental results obtained on 24, 48, and 96 ply graphite epoxy tension specimens which were spot-irradiated at various intensity levels.
The effect of fire on the tensile properties of carbon fibres is experimentally determined to provide new insights into the tensile performance of carbon fibre–polymer composite materials during fire. Structural tests on carbon–epoxy laminate reveal that thermally-activated weakening of the fibre reinforcement is the dominant softening process which leads to failure in the event of a fire. This process is experimentally investigated by determining the reduction to the tensile properties and identifying the softening mechanism of T700 carbon fibre following exposure to simulated fires of different temperatures (up to 700°C) and atmospheres (air and inert). The fibre modulus decreases with increasing temperature (above ∼500°C) in air, which is attributed to oxidation of the higher stiffness layer in the near-surface fibre region. The fibre modulus is not affected when heated in an inert (nitrogen) atmosphere due to the absence of surface oxidation, revealing that the stiffness loss of carbon fibre composites in fire is sensitive to the oxygen content. The tensile strength of carbon fibre is reduced by nearly 50% following exposure to temperatures over the range 400–700°C in an air or inert atmosphere. Unlike the fibre modulus, the reduction in fibre strength is insensitive to the oxygen content of the atmosphere during fire. The reduction in strength is possibly attributable to very small (under ∼100nm) flaws and removal of the sizing caused by high temperature exposure.
The a.c. dielectric breakdown and electrical resistivity of glass ceramics in the system MgO-Al2O3-SiO2-TiO2 have been studied using three sets of samples having different crystallinity contents. Standard a.c. (50 Hz) breakdown tests were performed at room temperature (18 °C) using planar disc specimens and hemispherically-ended brass contact electrodes. The breakdown process caused the formation of a breakdown channel which terminated at the specimen surface in a crater. The breakdown strength was independent of the rate of voltage rise, but decreased exponentially (60 to 10 kV mm-1) with increasing specimen thickness. A high crystallinity content, good surface finish and a homogeneous microstructure yielded high breakdown strengths whilst poor microstructural development caused a reduction in breakdown strength. The breakdown mechanism is believed to be a combination of electronic, thermal and electromechanical processes.
testing. Results show that the energy dissipated in a specimen during the lightning strike is much greater than the strain energy introduced by mechanical impact, and hence a comparison based on energy is not recommended. However, based on the relative threat levels associated with the impact and the lightning strike events, the comparison yields insightful observations on both damage state and residual performance. In general, for the configurations tested, lightning strike damage seems to be less detrimental than the mechanical impact in terms of both damage area and residual strength.
This paper is devoted to the study of unsteady electric arcs and the effects of electrodes on their dynamics. One of the objectives is to simulate and understand the three-dimensional behaviour of arcs in complex geometries, which create important fluctuations of the column and reattachments on the electrodes. The usual methods to solve the problem of arc–electrodes coupling are not suitable to simulate three-dimensional unsteady arcs. We propose a numerical development to simulate both steady-state and unsteady arcs without additional assumptions. The method is based on the incorporation of electrodes into the computational domain. It is validated with measurements from the literature, in the case of a point–plane steady-state argon arc. The model is used to study the lightning certification test device, which simulates in laboratory the effects of lightning arcs on fuselage panels. The results bring to light, in agreement with the observations in laboratory, the fundamental role of the electrodes on the three-dimensional behaviour of the arc column. The model is also used to simulate the development of the free jet of a plasma on an aluminium planar anode. The objective is to characterize the interaction region and the thermal constraint of the arc.
We present experimental data on mass removal during 1064-nm pulsed laser ablation of graphite, niobium and YBa2Cu3O7-δ superconductor. Evidence for the transition from normal vaporization to phase explosion has been obtained for these materials,
showing a dramatic increase in the ablation rate at the threshold fluences of 22, 15 and 17.5J/cm2, respectively. A numerical model is used to evaluate the ablation rate and temperature distribution within the targets under
near-threshold ablation conditions. The results are analyzed from the viewpoint of the vaporized matter approaching the critical
point with increasing laser fluence. A possible means of the estimating the thermodynamic critical temperature from the data
for nanosecond laser ablation is discussed. It is suggested that the critical temperature of refractory metals is higher than
that estimated with the traditional methods due to plasma effects. An analogy with the boiling crisis (the transition from
nucleate to film boiling) is drawn to explain the formation of ablation craters with spallated edges.
Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated lightning strike generator in the effort to understand the fundamental damage response of this material form. The strikes up to 50,000 A and 28,000 V are inflicted on both pristine specimens and specimens containing a Hilok stainless steel fastener. Damage area is evaluated via ultrasonic scanning, and advanced optical microscopy is used to gain further understanding in the morphology of damage. Subsequent mechanical testing to assess the residual tensile and compressive strength and modulus of the material is performed according to ASTM standards. Results show that residual tension strength counter intuitively increases after the infliction of damage, while residual compressive strength is much more dramatically and negatively affected. Furthermore, the presence of the fastener influences dramatically both the state of damage in the specimen and its residual strength by spreading throughout the thickness rather than limiting it to the specimen surface.
The goal of this chapter is to present the current state of the art of lightning interception, and to show how the computer simulation programs that accommodate the physics of lightning interaction could be used to complement the protection procedures based on either the electro-geometrical model or the rolling sphere method. First, let us explain the basics of the simple procedures used by engineers to protect structures from lightning flashes. Some of these procedures are explained also in Chapters 6 and 21. However, for the sake of completeness they are described here too.
During the pulsed laser ablation (PLA) of solid materials, the surface of the target material progressively recedes which in turn necessitates to account for the moving front boundary in the formulation of the laser heat conduction problem. Hence, developing an accurate predictive simulation model that captures the material moving front and updates simultaneously the laser source boundary conditions is an important and yet challenging task. In this paper, the PLA of aluminum is formulated and modeled with finite element analysis (FEA) that considers the instant material removal during the ablation process. Here, the implementation of such an FEA enables a strong coupling between the progressive surface recession (i.e., the shape change of the target material) and the laser heat conduction. Moreover, the proposed numerical simulation model not only predicts the progressive surface recession due to the material evaporation in the low laser fluence regime, but it also captures the ablation depth due to the material phase explosion in the high laser fluence regime. In addition, the temperature-dependent material and optical properties of the aluminum target are considered in the simulation. With nanosecond Nd:YAG 266 and 193 nm laser pulses, simulations are performed for the PLA of aluminum under various laser fluence. The predicted ablation depths under low laser fluence clearly show better agreement with experimental data, when compared to other predictions based on the hydrodynamics simulation model. Furthermore, the predicted threshold of the material phase transition in the high laser fluence regime also shows a good degree of consistency with experimental data.
A comprehensive simulation procedure combining electrical-thermal analysis and BLOW-OFF impulse (BOI) analysis was conducted to investigate lightning direct effects on damage behavior of composite. The nonlinear material model was elaborated combining the damage mechanism of composite laminate subjected to lightning strike. Results of electrical-thermal analysis indicated that temperature distribution of composite laminate is mainly affected by the electrical anisotropy because of Joule heating. By comparing results of BOI analysis with lightning test, it can be found that strain fields of analysis meet well with the damage pattern of lightning specimen. It could be concluded that the analysis procedure is suitable for modeling damage of composite due to lighting strike, and results of logarithmic strain field can be used to help estimate the zone which need to be repaired for composite.
A review of the classic techniques used to solve ablative thermal response problems is presented. The advantages and disadvantages of both the finite element and finite difference methods are described. As a first step in developing a three-dimensional finite element based ablative thermal response capability, a one-dimensional computer tool has been developed. The finite element method is used to discretize the governing differential equations and Galerkin's method of weighted residuals is used to derive the element equations. A code-to-code comparison between the current one-dimensional finite element tool and the one-dimensional Fully Implicit Ablation and Thermal response program (FIAT), a NASA-standard finite difference tool, has been performed. In addition, the three-dimensional computer tool has been developed and preliminary results from the three-dimensional tool are presented.
The breakdown strength as well as the mechanical strength of ceramic materials decreases with increasing volume. The volume-effect of the mechanical strength can be explained by the Weibull theory. For the breakdown strength the same explanation has been often assumed. In order to validate this assumption breakdown strength and mechanical strength of alumina samples with defined porosities were compared. Differences in the Weibull moduli of breakdown and mechanical strength distributions indicate that the volume-effect cannot explain the thickness-dependence of the breakdown strength. In particular, the thickness-dependence of the breakdown strength always leads to a Weibull modulus of two which is not in agreement with the measured Weibull moduli for samples with constant thickness. It can be concluded that the thickness-dependence of the breakdown strength cannot be explained by the Weibull concept. A recently developed breakdown model which is based on space charge injection is able to explain the experimental results.
Ablation damage characteristic of carbon fiber/epoxy composite laminate suffered from lightning strike was studied by the coupled thermal–electrical–structural analysis and element deletion. Residual strength of composite laminate after lightning strike ablation was globally predicted by Hashin criterion. Results show that lightning ablation effects decrease with the increasing electrical conductivity or specific heat, while thermal conductivity has little influence on them. Residual strength of composite laminate is generally greater than 80% and decreases with the increasing peak current or ratio of time to the maximum current and that to 50% of the maximum current under static tensile load. The work can provide detailed technical support for lightning damage evaluation and residual strength prediction of aircraft carbon fiber/epoxy composite laminates in theory, which is seldom reported compared with lightning test researches available up to now.
Carbon fiber-reinforced polymers, used in primary structures for aircraft due to an excellent strength-to-weight ratio when compared with conventional aluminium alloy counterparts, may nowadays be considered as mature structural materials. Their use has been extended in recent decades, with several aircraft manufacturers delivering fuselages entirely manufactured with carbon composites and using advanced processing technologies. However, one of the main drawbacks of using such composites entails their poor electrical conductivity when compared with aluminium alloy competitors that leads to lightning strikes being considered a significant threat during the service life of the aircraft. Traditionally, this problem was overcome with the use of a protective copper/bronze mesh that added additional weight and reduced the effectiveness of use of the material. Moreover, this traditional sizing method is based on vast experimental campaigns carried out by subjecting composite panels to simulated lightning strike events. While this method has proven its validity, and is necessary for certification of the structure, it may be optimized with the aid provided by physically based numerical models. This paper presents a model based on the finite element method that includes the sources of damage observed in a lightning strike, such as thermal damage caused by Joule overheating and electromagnetic/acoustic pressures induced by the arc around the attachment points. The results of the model are compared with lightning strike experiments carried out in a carbon woven composite.
A finite element ablation and thermal response program for the simulation of three-dimensional transient thermostructural analysis has been developed. The three-dimensional governing differential equations and finite element formulation are summarized. A novel probabilistic design methodology for thermal protection systems has been developed. The design methodology is an eight step process beginning with a parameter sensitivity study and is followed by a deterministic analysis whereby an optimum design can determined. The design process concludes with a Monte Carlo simulation where the probabilities of exceeding design specifications are estimated. The design methodology is demonstrated by applying the methodology to the carbon phenolic compression pads of the Crew Exploration Vehicle. The maximum allowed values of bondline temperature and tensile stress are used as the design specifications in this study. Using the design methodology, the probability of exceeding these design specifications was shown to be low and within an acceptable range.
This paper presents a physics based modelling procedure to predict the thermal damage of composite material when struck by lightning. The procedure uses the Finite Element Method with non-linear material models to represent the extreme thermal material behaviour of the composite material (carbon/epoxy) and an embedded copper mesh protection system. Simulation predictions are compared against published experimental data, illustrating the potential accuracy and computational cost of virtual lightning strike tests and the requirement for temperature dependent material modelling. The modelling procedure is then used to examine and explain a number of practical solutions to minimize thermal material damage.
Composite materials have a wide application in aerospace, automotive,
and other transportation industries, because of the superior structural
and weight performances. Since carbon fiber reinforced polymer
composites possess a much lower electrical conductivity as compared to
traditional metallic materials utilized for aircraft structures, serious
concern about damage resistance/tolerance against lightning has been
rising. Main task of this study is to clarify the lightning damage
mechanism of carbon fiber reinforced epoxy polymer composites to help
further development of lightning strike protection. The research on
lightning damage to carbon fiber reinforced polymer composites is quite
challenging, and there has been little study available until now. In
order to tackle this issue, building block approach was employed. The
research was started with the development of supporting technologies
such as a current impulse generator to simulate a lightning strike in a
laboratory. Then, fundamental electrical properties and fracture
behavior of CFRPs exposed to high and low level current impulse were
investigated using simple coupon specimens, followed by extensive
parametric investigations in terms of different prepreg materials
frequently used in aerospace industry, various stacking sequences,
different lightning intensity, and lightning current waveforms. It
revealed that the thermal resistance capability of polymer matrix was
one of the most influential parameters on lightning damage resistance of
CFRPs. Based on the experimental findings, the semi-empirical analysis
model for predicting the extent of lightning damage was established. The
model was fitted through experimental data to determine empirical
parameters and, then, showed a good capability to provide reliable
predictions for other test conditions and materials. Finally, structural
element level lightning tests were performed to explore more practical
situations. Specifically, filled-hole CFRP plates and patch-repaired
CFRP plates were selected as structural elements likely to be
susceptible to lightning event. This study forms a solid foundation for
the understanding of lightning damage mechanism of CFRPs, and become an
important first step toward building a practical damage prediction tool
of lighting event.
Heatshield design and analysis has traditionally been a decoupled
process, the designer creates the geometry generally without knowledge
about how the design variables affect the thermostructural response or
how the system will perform under off nominal conditions. Heatshield
thermal and structural response analyses are generally performed as
separate tasks where the analysts size their respective components and
feedback their results to the designer who is left to interpret them.
The analysts are generally unable to provide guidance in terms of how
the design variables can be modified to meet geometric constraints and
not exceed the thermal or structural design specifications. In general,
the thermal response analysis of ablative thermal protection systems has
traditionally been performed using a one-dimensional finite difference
calculation. The structural analyses are generally one, two, or
three-dimensional finite element calculations. In this dissertation, the
governing differential equations for ablative thermal response are
solved in three-dimensions using the finite element method. Darcy' Law
is used to model the flow of pyrolysis gas through the ablative
material. The three-dimensional governing differential equations for
Darcy flow are solved using the finite element method as well.
Additionally, the equations for linear elasticity are solved by the
finite element method for the thermal stress using temperatures directly
from the thermal response calculations. This dissertation also links the
analysis of thermal protection systems to their design. The link to
design comes from understanding the variation in the thermostructural
response over the range of the design variables. Material property
sensitivities are performed and an optimum design is determined based on
a deterministic analysis minimizing the design specification of bondline
temperature subject to appropriate constraints. A Monte Carlo simulation
is performed on the optimum design to determine the probability of
exceeding the design specifications. The design methodology is
demonstrated on the Orion Crew Exploration Vehicle's compression pad
design.
Superior structural capabilities and lightweight of carbon-fibre-reinforced polymer composites have made their applications
increasingly noticeable particularly in the aerospace and automotive industries for reduced fuel consumption. Anisotropic
and heterogeneous features of these materials, however, have been prohibiting the application of laser cutting on these materials
in industrial scale. In the present study the thermal degradation characteristics in laser cutting of these materials are
investigated with a nano-second pulsed diode pumped solid state Nd:YAG. A statistical analysis was performed for the optimisation
of the process parameters. Furthermore, quality improvement was achieved by the use of low oxygen content assistant gas simultaneously
with the inert gas shield. The controlled presence of oxygen as a burning mechanism reduced the fibre pull out up to 55% at
the same time with a high processing rate.
This study examines the evolution of damage in graphite/epoxy composite laminates due to lightning strikes. To clarify the influence of lightning parameters and specimen size, artificial lightning testing was performed on a series of laminated composite specimens. Damage was assessed using visual inspection, ultrasonic testing, micro X-ray inspection, and sectional observation. The results showed that the damage modes can be categorized into fiber damage, resin deterioration, and internal delamination modes. Damage progression is governed by the strong electrical orthotropic properties of the laminates, and the lightning parameters defining impulse waveform show strong relationship with certain damage modes, though specimen size and thickness variation barely affect damage size.
The magnetic pressure in a cylindrical wire has been calculated for constant current, steady-state sinusoidal current, and the pulse current of an overdamped discharge. As previously shown by Haines (1959) for conductors carrying time-varying currents, an inverse current density distribution is produced corresponding to an `inverse skin effect'. Maninger (1959) and Haines predicted that the inverse skin effect also creates an inverse pinch effect, thereby producing an outer shell of magnetic tension in the wire. A quantitative analysis for a pulse current-carrying conductor shows that the inverse pinch effect becomes dominant over the normal pinch effect in later time instants of the current pulsing. The distribution of the magnetic pressure in a rectangular rod carrying a constant current has been calculated for different ratios of thickness and width. The validity of this solution for thin foils is discussed for the case of applied alternating currents.
Based on the lightning leader model of Cooray et al., the electric field distribution on a wind turb ine induced by the leader has been simulated using the Finite Element Method. Due to its dimensions and complexity, the wind turbine has been simplified to its lightning protection system and b y simulating only one blade. The derived electric field distribu tion has then been used as input for a detailed blade-tip model. The detailed model can be used to analyze the influence of the d own-conductor shape on the electric field strength. Furthermore, the influence of the electric field on the down-conductor insulation is addressed.
This paper proposes the use of the 'LTE-diffusion approximation' for predicting the properties of electric arcs. Under this approximation, local thermodynamic equilibrium (LTE) is assumed, with a particular mesh size near the electrodes chosen to be equal to the 'diffusion length', based on De/W, where De is the electron diffusion coefficient and W is the electron drift velocity. This approximation overcomes the problem that the equilibrium electrical conductivity in the arc near the electrodes is almost zero, which makes accurate calculations using LTE impossible in the limit of small mesh size, as then voltages would tend towards infinity. Use of the LTE-diffusion approximation for a 200 A arc with a thermionic cathode gives predictions of total arc voltage, electrode temperatures, arc temperatures and radial profiles of heat flux density and current density at the anode that are in approximate agreement with more accurate calculations which include an account of the diffusion of electric charges to the electrodes, and also with experimental results. Calculations, which include diffusion of charges, agree with experimental results of current and heat flux density as a function of radius if the Milne boundary condition is used at the anode surface rather than imposing zero charge density at the anode.
This paper presents a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire. Models for analysing the thermal, chemical, physical, and failure processes that control the structural responses of laminates and sandwich composite materials in fire are reviewed. Models for calculating the residual structural properties of composites following fire are also described. Progress towards validation of the models by experimental characterisation of the structural properties of composites during and following fire is assessed. Deficiencies in the fire structural models are identified in the paper, which provide the focus for future research in the field.
First return stroke current waveforms measured by Berger [Methods and results of lightning records at Monte San Salvatore from 1963–1971 (in German), Bull. Schweiz. Elektrotech. ver. 63 (1972) 21403—21422] and Berger and Vogelsanger [Measurement and results of lightning records at Monte San Salvatore from 1955–1963 (in German), Bull. Schweiz. Elektrotech. ver. 56 (1965) 2–22] are used to estimate the charge stored in the lightning stepped leader channel. As opposed to previous charge estimates based on the entire current waveform, only the initial portion of measured current waveforms (100 μs in duration) was used in order to avoid the inclusion of any charges not involved in the effective neutralization of charges originally stored on the leader channel. The charge brought to ground by the return stroke within the first 100 μs, Qf,100 μs (in C) is related to the first return stroke peak current, Ipf (in kA), as Qf,100 μs=0.61 Ipf. From this equation the charge distribution of the stepped leader as a function of the corresponding peak return stroke current is estimated. This distribution (along with the assumed average electric field of 500 kV/m in the final gap) is used to estimate the lightning striking distance S (in meters) to a flat ground as a function of the prospective return stroke peak current I (in kA): S=1.9 Ipf0.90. For the median first stroke peak current of 30 kA one obtains S=41 m, while the traditional equation, S=10 Ipf0.65, gives S=91 m. In our view, the new equation for striking distance provides a more physically realistic basis for the electro-geometric approach widely used in estimating lightning incidence to power lines and other structures.
The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined experimentally following an experimental technique developed previously. The results indicate that arc length is the primary variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6 mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported.
Cyclic mixed mode delamination in multidirectional composite laminates subjected to high cycle fatigue loading has been investigated by numerical simulations and cyclic mixed mode bending experiments. The numerical model includes lamina and interface elements. The description of the delamination crack growth rate is based on the cyclic degradation of bilinear interface elements linking the evolution of the damage variable with the delamination crack growth rate. The constitutive cyclic damage model is calibrated by means of mixed mode fatigue experiments and reproduces the experimental results successfully and with minor error. It is concluded that only with implementing a cyclic damage variable in the cohesive interface element the experimentally observed crack growth and stiffness degradation can be captured properly. Scanning electron microscopy of fracture surfaces after cyclic loading revealed that abrasion of crack bridging surface roughness is the main microscopical cause of weakening and degradation of the interface.
A study of laser ablation of Aluminum sample by nanosecond laser pulses considering two simultaneous mechanisms of normal evaporation and phase explosion is theoretically carried out. The temperature distribution in the sample is calculated by a one dimensional heat conduction equation. Ablation depth due to the evaporation and explosion is calculated as a function of laser pulse energies. Variation in some effective sample parameters during the laser ablation and their effects on laser ablation mechanisms are taken into account. At low irradiance, ablation is mainly due to the evaporation, while after a threshold intensity, the phase explosion becomes the dominant mechanism. Theoretical results of transition from the normal evaporation to the phase explosion are in good agreement with the experimental results.
Heat transfer intensity and current density distributions at the anode of high current arcs in predominantly inert gas atmospheres were determined experimentally. Measurements were made for stable, axially symmetric arcs having a small diameter refractory metal cathode and a plane, cooled copper anode. The experimental method consisted of splitting the anode, measuring the heat flux and the current to one of the sections as a function of arc position relative to the splitting plane, and calculating therefrom the distribution functions. The work encompassed the effects of gas pressure (195–790 mm Hg), cathode geometry and material (tungsten and W‐1% ThO 2 ), electrode separation (1.6–12.7 mm), arc current (100–300 amp), gas composition (argon, helium, and diatomic gas‐argon mixtures), and localized constriction of the plasma column. Peak heat transfer intensities ranged from 1.0 to 20 kw/cm2 and peak current densities from 100 to 2500 amp/cm2. The heat and current distribution curves were of similar shape and were generally sharper than Gaussian. The heat distributions were partially resolved according to transfer mechanism. An upper limit was set on the average kinetic energy of electrons arriving on axis at the anode. This was used to specify limits on gas heat transfer intensities for certain conditions. The space charge sheath at the anode was estimated to be 10-4 to 10-3 cm thick at the arc axis.
Non-metallic structural materials that act as an electrical insulation are needed for cryogenic power applications. One of the extensively utilized materials is glass fiber reinforced resins (GFRR) and may also be known as GFRP and FRP. They are created from glass fiber cloth that are impregnated with an epoxy resin under pressure and heat. Although the materials based on GFRR have been employed extensively, reports about their dielectric properties at cryogenic temperatures and larger thicknesses are generally lacking in the literature. Therefore to guide electrical apparatus designers for cryogenic applications, GFRR samples with different thicknesses are tested in a liquid nitrogen bath. Scaling relation between the dielectric breakdown strength and the GFFR thickness is established. Their loss tangents are also reported at various frequencies.
A high-temperature fibre-testing apparatus has been designed. It is dedicated to the determination of various properties at very high temperatures, including electrical conductivity, Young's modulus, thermal expansion coefficient, strength. Test temperatures as high as 3000 °C can be applied to carbon fibres. Two types of carbon fibres (a PAN-based and a Rayon-based fibre) have been investigated at temperatures up to 2000 °C. The measured properties are discussed with respect to microstructural features.
A coupled thermal–electrical analysis of carbon fiber reinforced polymer composites (CFRP) exposed to simulated lightning current was conducted in order to elucidate the damage behavior caused by a lightning strike with the numerical results being compared to experimental results. Based on the experimental results and a preliminary analysis, the specific mechanism of electrical conduction through the thickness direction of CFRP following thermal decomposition was revealed to be a key parameter for accurate numerical simulation. In particular, assuming the electrical conductivity in the thickness direction to be linear with respect to temperature in the range from the epoxy decomposition temperature to carbon sublimation temperature produced reasonable numerical results. The delamination area and damage depth were estimated from numerical results and thermal decomposition behavior of CFRP with the estimated damage area agreeing qualitatively with the experimental results. Numerical results suggest that Joule heat generation significantly influences lightning strike damage.
Lightning damage of Owecs, part 1: parameters relevant for cost modelling
- H Braam
Braam H. Lightning damage of Owecs, part 1: parameters relevant for cost
modelling. ECN-C-02-053; 2002.
Lightning direct effects handbook
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