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Lightning ablation damage and residual bending performances of scarf-repaired composite laminates with copper mesh protection
... This protection method has proven its efficiency [3] but does not protect the aeronautical structure entirely and implies maintenance and flying down-time to repair the sacrificed layer, resulting in additional cost [4]. Recent studies [5] notably point out the influence of the paint thickness, increasing the damage observed in the core of composite laminates subjected to lightning strikes ( Figure 2). ...
Lightweight aeronautical structures and power generation structures such as wind turbines are fitted with protected external layers designed and certified to withstand severe climatic events such as lightning strikes. During these events, high currents flow through the structural protection but are likely to induce effects deeper in the supporting composite material and could even reach or perforate pressurized tanks. In situ measurements are hard to achieve during current delivery due to the severe electromagnetic conditions, and the lightning strike phenomenon on these structures is not yet fully investigated. To gain a better understanding of the physics involved, similarities in direct damage between lightning-struck samples and those subjected to pulsed lasers and an electron gun are analyzed. These analyses show the inability of a pure mechanical contribution to fully reproduce the shape of the delamination distribution of lightning strikes. Conversely, the similarities in effect and damage with the thermomechanical contribution of electron beam deposition are highlighted, particularly the increase in core delamination due to the paint and the apparent similarities in delamination distribution.
... This protection method has proven its efficiency [3] but does not protect the aeronautical structure entirely and implies maintenance and flying down-time to repair the sacrificed layer, resulting in additional cost [4]. Recent studies [5] notably point out the influence of the paint thickness, increasing the damage observed in the core of composite laminates subjected to lightning strikes ( Figure 2). ...
The study of post lightning strike residual strength is still relatively underdeveloped in the literature. Different approaches including in-plane compression or flexural testing have been used, but in-plane tensile loading post-strike has not been studied in detail. Although previous attempts have been made to determine the residual strength using Compression-After-Lightning (CAL) tests on composite laminates, these have been limited and not readily applicable under tensile loads. Therefore, this work completes Tension-After-Lightning (TAL) testing at 75 kA on composite laminates, a more realistic peak current than previously reported for TAL tests, to assess the knock-down in strength post-strike. The measured average TAL failure stress was 716 MPa, a reduction of 23 % from the baseline tensile failure stress of 929 MPa in the literature. This confirms a similar knock-down factor reported at lower peak currents (e.g. 50 kA), but the new TAL specimen geometry ensures that the lightning damage is contained within both the lightning and TAL specimen widths. In addition, a new Finite Element (FE) based virtual test was conducted, considering 0° ply splitting, and validated with the TAL tests herein. The TAL simulation predicted the residual tensile failure stress well, within 6 % of the measured value.
The effectiveness of patch bonding repair depends on the mechanical and geometric properties of the adhesive and patch, which ensure proper load transfer without damaging the adhesive layer. Maintaining an optimal stiffness ratio between the plate and patch is crucial, often requiring adjustments to the stacking sequence or patch geometry. While various geometric modifications have been proposed to enhance structural durability, few studies have explored modifications to the damaged metal plate itself. This study presents a numerical analysis of composite patch repairs on damaged aluminum plates, incorporating geometric modifications to improve fracture strength. The investigation employs finite element modeling to evaluate the impact of material removal at the damaged area on fracture behavior, with and without repair. Key parameters analyzed include J-integral values at the crack tip, Von Mises stresses in the adhesive layer, patch geometry, and plate thickness variations. Results demonstrate that a 0.2 mm material removal does not induce excessive stress concentrations, ensuring structural integrity under low loads. When reinforced with a composite patch, even under higher loads, the modified plate exhibits superior strength compared to an unmodified one. Optimizing adhesive properties and plate thickness further increases the repair performance, significantly reducing J-integral values by mitigating bending effects caused by the asymmetric repair.
The patch repair is a widely used method for repairing the damaged composite structure, optimizing the repair structure in considering static strength and fatigue life can greatly improve the reliability and safety. However, only static strength and fatigue life are considered during the design or optimization. In this paper, the multi-objective optimization of composite laminate repaired by patches in considering static strength and fatigue life was carried out. The models used for predicating static strength and fatigue life were established through Finite Element Method. Then, the established models were adopted to investigate the effect of repair parameters on static strength and fatigue life, results show that patch radius has the strongest impact on static strength and fatigue life, while the repair thickness and stacking sequence of patch show a greater impact on fatigue life. Based on the above conclusions, Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to optimize the repair structure. The optimization results show that strength and fatigue life was greatly improved, the repair thickness and patch volume was greatly reduced, patches that radius is larger than 14mm can ensure that the repair structure has both higher strength and better fatigue resistance. The proposed optimization method has a good optimization effect for composite laminate repaired by patches.
Compressive performances of composite structures can be significantly decreased due to the lightning strike damage, so the structures with lightning frighten must be considered lightning protection design. In this study, compressive experiments after lightning strikes were conducted on non‐protected, 12‐layer interlaminar carbon nanotube film (CNF) protected, and traditional surface silver coating (TSSC)‐protected composite laminates. A numerical analysis procedure was established, incorporating a lightning strike ablation damage simulation (LSADS) module and compressive residual strength calculation (CRSC) module. The procedure's effectiveness was verified by the experiment results. Based on this procedure, the compressive performances and the possible failure mechanism of laminates after lightning strikes were analyzed. The results show that the laminates with TSSC protection and 12‐layer interlaminar CNF protection can increase compressive residual strength compared with non‐protected laminates. The predominant compressive damages of the laminates after lightning strikes are fiber‐matrix shear damage and fiber fracture damage. Optimized one‐layer interlaminar CNF protection with a thickness of 0.36 mm can increase the laminate compressive strength but decrease the structural weight. This study offers a reference and basis for the lightning strike protection design of composite structures.
Highlights
CNF in lightning strike protection of composite structures.
Compressive failure mechanism of composite laminates after lightning strikes.
A numerical procedure to evaluate lightning damage and compressive performances.
Design of interlaminar CNF protection.
Carbon Fiber Reinforced Plastics (CFRPs) composite structures are widely used in aeronautical structures. Due to the semiconducting nature of CFRPs, lightning strikes can cause significant damages in aircraft components made from such materials. In CFRP laminates joined by mechanical fasteners or adhesive bonding, the damage induced by lightning strikes is a complex multiphysics coupling process. In the present work, in order to study the effects of the different lightning current components on CFRP joints due to the Joule heat flux phenomenon, a coupled electro-thermal FE model has been developed using the ANSYS commercial FE code. Two case studies are considered, i.e. a bolted single-lap joint and an adhesively bonded single-lap joint of CFRP laminates. The model is based on the SOLID5 coupled field solid element and applies a non-linear, time-transient analysis. The main input to the model are the thermal-electrical properties of the CFRP material which vary with temperature. Three electrical lightning strikes of low, medium, and high peak intensity have been applied according to the SAE ARP 5412 standard. The numerical results reveal the detrimental effect of the lightning strike on the bolted joint of the riveted case as the electro-thermal conditions on the bolt facilitated the through-the-thickness degradation of the CFRP material, as opposed to the adhesively bonded joint where the increase of the peak intensity has led to an escalation of the area and penetration of matrix thermal damage (pyrolysis) as well as to the increase of fiber damage (deterioration and ablation). Through static mechanical analysis, the residual joint stiffness has been also predicted.
A review of the development and the usages of traditional non-internal state variable (ISV) models and ISV theory for modeling behaviors of composite materials are presented in this paper. The history of earliest composites models for predictions of material stiffness, failure, viscoelasticity and plasticity is discussed first. Then following the ISV theory, a fundamental thermodynamic framework that governs the dissipative effects caused by the inelastic phenomena is introduced. Applying the thermodynamic restrictions obtained from that framework, different researchers have employed the ISV theory to develop constitutive models for composites to capture their viscoelas-ticity, rate-independent plasticity, viscoplasticity, and continuum damage. ISVs introduced into those models for describing each inelastic behavior of composites as well as their evolution rules are also discussed. The knowledge obtained from this review in terms of the usages of the ISV theory for composite material modeling forms a theoretical background for the development of a general modeling framework to predict all inelastic phenomena of a wide variety of composite materials. ARTICLE HISTORY
：According to simulation lightning experiments and eddy current analysis results, a three-dimensional finite element model of composite laminated plates with shield is established. By applying electric-thermal boundary and the coupling relationship between them, the lightning strike damage results under the protection of shield are realistically simulated with the commercial finite element analysis software, ABAQUS. Considering the coupling effect of heat, electricity, and force during lightning strike, the load distribution field of copper mesh and carbon fiber panel with lightning current inducted is analyzed. Comparing the thermal stress distribution of the specimen surface under various current loads, it is shown that the stress of carbon fiber panel is significantly lower than the one of the copper screen when the specimen structure suffers heavy current, since the copper network plays a role of endergonic protection. Simulation data are consistent with the test results, thus the method can be used for other similar research.
A kind of interlaminar film with carbon nanotubes inserted into polyether ketone with cardo was used for lightning strike protection of composite laminates. The distribution of the interlaminar film was investigated by experimental and numerical methods. Artificial lightning strike tests were conducted for 12-film carbon nanotube and traditional surface silver coating protected specimens. Then corresponding finite element models (FEMs) were established to analyze the lightning strike effect and validated by the experimental results. Based on the FEMs, the number, distribution and thickness of interlaminar film were investigated in order to obtain equivalent protection effect with the traditional surface silver coating. The results show that only the first two layers were damaged for the surface silver coating protected specimen, while 5 layers were ablated for the 12-film protected specimen. Lightning strike damage area of the laminate protected with 5-film carbon nanotube is almost the same as that of the laminate protected with 12-film carbon nanotube. Compared with traditional surface silver coating protection, one film protection with thickness of 360 μm can make the laminate to obtain equivalent damage depth, 54.8% smaller damage area and 58% less additional weight. And reparability of the laminate is better than that of the laminate protected with 5 interlaminar films.
This paper presents a novel, meshfree-based micromechanical model for homogenising the elastic properties and analysing the deformation and microscopic strains/stresses of twill woven composites. The proposed model was based on a minimum unit cell (mUC) whose internal features such as the cross-sectional shape and waviness of yarns were described by using sophisticated functions. The boundary conditions imposed on the mUC were derived by applying an equivalence approach, which converts the standard form of periodic boundary conditions into a generic set of fixed and relative displacement constraints. Theoretical formulations were developed to implement the micromechanical model within the framework of the moving kriging (MK)-based element-free Galerkin (EFG) method. An in-house computer program implementing the proposed model was developed for analysing a typical twill woven composite. Good agreements were found between the meshfree-based predictions and the reference results, highlighting the proposed model capable of homogenising twill woven composites and meanwhile avoiding the commonly required pre-processing tasks such as building an explicit geometry model and generating identical meshes on the mapping surfaces to enforce boundary conditions. Three case studies were also performed to identify the sensitivities of the predicted results to three numerical parameters, i.e. the total number of field nodes, the total number of background cells, and the support domain scaling factor. The results of these studies suggest that the numbers of field nodes and background cells used must be sufficiently large, while the support domain scaling factor in an appropriate range (e.g. 2.0–3.25) to achieve convergent results.
In composite aircraft structures, woven carbon-fibre reinforced plies are often used as the surface plies of a monolithic composite panel, made from unidirectional plies, to mitigate damage during drilling and provide a measure of impact damage resistance. This research presents, for the first time, a detailed experimental and numerical study on the crush behaviour of hybrid unidirectional/woven carbon-fibre reinforced composite laminates. Quasi-static crush tests are performed on composite specimens with two different trigger geometries; a bevel-trigger and a steeple-trigger. A computational model, which accounts for both interlaminar and intralaminar damage in hybrid unidirectional (UD)/woven composite laminates, implemented as a user subroutine in Abaqus/Explicit, was used. A comparison between experimental and numerical results confirms the computational tool's accuracy in predicting the energy absorption and damage mechanisms of hybrid specimens. The proposed approach could significantly reduce the extent of physical testing required in the development of crashworthy structures.
Both single-face vacuum bag curing (SVC) and double-face vacuum bag curing (DVC) can be used in scarf repair of composite structures. But different curing conditions caused by the sealing state may affect the bonding quality of scarf-repaired structures. In this paper, the effect of curing condition on bonding quality of scarf-repaired laminates was experimentally investigated in terms of surface profiles, moisture absorption curves and section profiles. In order to further explore the moisture absorption mechanism, finite element model of the repaired laminates using DVC was established with moisture diffusion of both the adhesive and composite laminates considered. This model was verified by experimental results. Based on the model of DVC case, the model of SVC case was built by changing moisture absorption parameters of the adhesive. Results show that SVC reduces the bonding quality, mainly reflecting in more adhesive inner voids and patch-to-parent dislocation. And SVC increases moisture absorption rate and moisture equilibrium content of the adhesive, and its effect on the former is far greater than that on the latter.
The research and development of graphene and graphene‐based materials have been significantly increasing since they were invented. However, in many industries, the applications of graphene nanoflakes are still few, compared with other materials. This study presents the fabrication of highly conductive graphene thin film (GTF) papers to reduce the possible damage of lightning strikes on composite structures. Three concepts were presented in this project: (1) fabrication of a highly conductive functionalized nanosize GTF, (2) incorporation of the GTF into carbon fiber‐reinforced composite panels, and (3) introduction of 3D stitching concepts into composite structures to protect against the effects of lightning strikes. Experimental studies have shown that the highest electrical and thermal conductivity values measured on GTF papers are approximately 1,800 S/cm and 425 W/m.K, respectively. After GTF was incorporated into the carbon fiber‐reinforced composites, some delamination was observed between the GTF and the composite. Therefore, the 3D stitching concept was introduced to reduce this delamination. Four stitch configurations with different stitch lengths, thread‐to‐thread thicknesses, thread tensions, and thread thicknesses were used. Then, tensile tests were carried out on the prepared unidirectional fiber composite test coupons. Although the delamination was completely eliminated, tensile strength on some of the test configurations was reduced. This study will be useful in increasing the electrical and thermal conductivity values of composite surfaces in aircraft and wind energy industries. POLYM. COMPOS., 40:E517–E525, 2019. © 2018 Society of Plastics Engineers
The effects of particularly heavy lightning strikes on representative carbon fibre reinforced plastics composite airframe structures, specifically with epoxy matrix systems, which are common within the aerospace industry, have been investigated in this study. The applied action integrals of the lightning strikes significantly exceed the requirements for airworthiness. All tests were performed with conventional prepreg materials and resin transfer moulding/non-crimp fabric materials with high lightning strike current ratings. The pristine panels exhibit major damage zones around the impact points. The results of non-destructive investigations show that the surface damage is predominantly superficial. Only small zones were considerably damaged where extensive repair was necessary. Carbon fibre reinforced plastics panels featuring repair patches were also investigated. Lightning strikes were placed above the scarf and the damage was analysed by various non-destructive investigation methods including micro-computed tomography. In contrast to the pristine panels, the repaired panels reveal different damage behaviour. The damaged zone on the surface was relatively small. In the tapered zone of the patch, electric flashovers between the patch and the base material were observed. Additional microscopy investigations show that these electric sparks also occur inside within the adhesive layers between the patch and the base material. After enhancing the electrical conductivity of the adhesive by adding carbon nanotubes, these difficult-to-detect electric sparks within the layers disappear.
This paper deals with three-point flexure tests on hybrid I- and Π-beams, made out of multi-layer carbon fibre/epoxy resin (including twill woven fabric CF3031/5284 and unidirectional cord fabric U3160/5284) reinforced composites, processed using the RTM (resin transfer moulding) technique. Static bending properties were determined and failure initiation mechanism was deduced from experimental observations. Failure mode of the tested hybrid RTM-made I-beams can be reckoned to be characteristic of the delamination from the cutout edge within the web and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until local buckling within the curved webs around the conjunction fillet region. In contrast, as distinct from hybrid RTM I-beams subjected to three-point bending loading, hybrid RTM-made Π-beams in three-point flexure tests experienced the resin debonding in the inverted triangular resin-rich zones and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until complete separation of the curved web from the flange. Progressive damage models (PDMs) were presented to predict failure loads and process of hybrid RTM-made I- and Π-beams under three-point flexure. Good correlation was achieved between experimental and numerical results.
Composite structures used in aircraft are vulnerable to low-velocity impact and replacing them with new ones requires significant cost. Scarf-repair technique is an effective method to restore the stiffness and strength of damaged composite structures. Previous studies on scarf-repaired composite laminates have focused on stiffness and strength recovery efficiency, but limited attention has been directed toward the impact properties. However, scarf-repaired composite laminates are also sensitive to low-velocity impact. The residual strength is worth investigating to ensure the safety of scarf-repaired composite structures. In this study, experiments were conducted to test the residual compression strength after impact. Two main factors, namely impact energy and location, were considered. Finite element models were established to analyze the influences of these two factors and to predict the residual strength. Impact damages were introduced by degrading the mechanical properties in the damaged area estimated through the C-scan photographs. Results indicated that the damage area was larger when the impact was applied at the bondline of the top surface and the residual strength was the smallest. Increasing the impact energy caused large damage area, in which the residual strength declined. The predicted residual strength agreed with the experimental results well.
This paper presents a multiscale modeling approach for the progressive failure analysis of carbon-fiber-reinforced woven composite materials. Hierarchical models of woven composites at three different length scales (micro, meso, and macro) were developed according to their unique geometrical and material characteristics. A novel strategy of two-way information transfer is developed for the multiscale analysis of woven composites. In this strategy, the macroscopic effective material properties are obtained from property homogenizations at micro and meso scales and the stresses at three length scales are computed with stress amplification method from macroscale to microscale. By means of the two-way information transfer, the micro, meso and macro structural characterizations of composites are carried out so that the micromechanisms of damage and their interactions are successfully investigated in a single macro model. In addition, both the nucleation and growth of damages are tracked during the progressive failure analysis. A continuum damage mechanics (CDM) method is used for post-failure modeling. The material stiffness, tensile strength and damage patterns of an open-hole woven composite laminate are predicted with the proposed multiscale method. The predictions are in good agreement with the experimental results.
Carbon fiber/epoxy composite specimens are manufactured using liquid resin infusion and incorporate a copper wire mesh on the outer layer for lightning strike protection. The specimens are then painted in order to be representative of an aircraft skin. The specimens are subjected to a scarf repair, which removes a portion of the wire mesh and of the carbon fiber substrate. The bonded repair is performed to re-establish the structural and electrical integrity of the laminate. Purpose of the study is to evaluate the effect of repair procedure on the structural performance of the carbon/epoxy specimens following a lightning strike, and in particular it is aimed at comparing the two extreme cases where full electrical conductivity is re-established, and where the electrical conductivity is interrupted. To do so, the copper wire mesh is re-applied during the repair following two scenarios. The first, denoted as “good” repair, involves overlapping part of the repair mesh with the parent mesh surrounding the repair area, while the second, referred to as “poor” repair, involves applying a repair mesh that is shorter than the parent mesh, thereby leaving a gap in the electrical path. The repaired specimens are then subjected to simulated lightning strike at the location of the repair. The damage resistance characteristics of the repaired specimens are compared to the benchmark values of unprotected specimens (i.e. without copper mesh) and protected pristine specimens (i.e. without repair). Residual strength testing using four-point bend flexure is used to assess the damage tolerance behavior of the specimens. Results show that a “good” repair performs as well as the pristine protected specimen, while a “poor” repair performs equally or worse than a fully unprotected specimen.
Composites are increasingly preferred in industrial, medical, and sporting applications due to their exceptional mechanical, electrical, thermal, and physical properties, as well as their low weight and investment costs, particularly in medical, electronics, aerospace, and automotive sectors. Impact damage to composite materials is a significant design issue, necessitating a thorough understanding of how these materials break down and fail under impact loads to ensure reliable and cost-effective design. This paper uses both experimental and numerical methods to present an in-depth review of the impact properties of composite materials.
The impact and tension-after-impact behaviors of scarf-repaired composites were investigated. Low-velocity impact tests were performed to determine the impact responses and impact damages. And the influences of impact damages on the residual tensile strength and failure modes were discussed. Then numerical models were proposed to elucidate the impact damage mechanism and predict the residual tensile strength. The numerical results agree well with the test results and indicate that delamination initiates early during the impact process, followed by matrix damage, while adhesive damage occurs at the last. And the main reason for tensile strength reduction is adhesive damage caused by pre-impact.
Previous works have studied the performance of well-established stepped scarf repair schemes for highly loaded composite structures. However, none of the proposed repair schemes appear to minimise healthy material removal. Thus, this paper, proposes a Variable Length Stepped Scarf (VLSS) scheme, which minimises healthy material removal. In addition, various standard schemes with overlap step length (1/60, 1/45 and 1/30) are studied. Both experimental and simulation (FEA) investigations are undertaken and for the first time, the quality of scarf is inspected by artificial-intelligence based machine vision. The experimental results show the VLSS scheme is comparable to the other repair designs in restoring structural stiffness of the intact structure. The VLSS shows the ability to restore ≈95% stiffness of the pristine structure compared to 91.4% of the largest repair scheme (overlap step length =1/60). However, the VLSS scheme falls short in restoring the static strength of the structure, with an efficiency of 64%. By contrast, the largest repair scheme shows a superior strength repair efficiency ≈77% and demonstrates a desirable failure response, i.e. fibre fracture in both repair patch and parent laminate.
The paper focused on the moisture absorption and hygrothermal degradation of composite laminates repaired via double scarf method. Experimental works were carried out on double scarf-repaired composite laminates to elucidate the effect of hygrothermal aging on the failure strength and failure mode. Finite element models were established to study the moisture distribution in the composite laminates and adhesive layer. And a progressive damage model considering the moisture gradient was subsequently proposed to predict the strength and analyze the damage mechanism. At last, the effects of overlap patch and moisture content on the failure strength were discussed.
SHPB system was widely used to investigate the dynamical mechanical performances of materials. In this study, the mechanical performances of T700/BA9916 composite material were investigated through experiment and numerical simulation. The true stress-strain curves of composite samples were obtained, and the influences of temperatures and strain-rates on the mechanical performances of composite samples were discussed. The finite element model of SHPB setup was established, and the compression mechanical performances of composite samples were simulated. T700/BA9916 composite material exhibited significant temperature softening and strain-rate enhancement effect during experimental. The compression failure strength and elastic modulus increased with the increase in strain-rates while the failure strain decreased. The compression failure strength and elastic modulus decreased with the rise in temperatures while the failure strain increased. The composite samples didn’t exhibit typical brittle failure at high temperature but significant temperature softening effect. A plateau phase existed between incident wave and reflection wave, and the slope of plateau phase was small when temperatures were low while that was large when temperatures were high. The numerical results were compared with experimental results to validate the proposed numerical method can be used to simulate the mechanical performances of composite materials.
The over-ply covering the bondline in scarf-repaired laminates can avoid direct exposure of the adhesive to moisture environment which would decrease the properties of the adhesive. The effect of the over-ply on moisture absorption behavior of scarf-repaired composite laminate was studied in this paper. 3D finite element models (FEMs) of scarf-repaired laminates with and without over-ply were established to simulate the moisture absorption behavior and verified by experimental results. Then these models were used to investigate the effects of some factors, including over-ply type, configuration, direction and number, on moisture absorption behavior of the repaired structures, especially of the adhesive. The results show that the over-ply can efficiently decelerate moisture absorption of the adhesive and delay the time of its moisture absorption equilibrium. Over-ply type has effect on moisture absorption of the adhesive. Woven over-ply is more effective to protect the adhesive in repaired laminates from moisture absorption than unidirectional over-ply. For the laminates with only large-circle bonding surface covered, over-ply lap length, configuration and direction are not very important parameters to affect the moisture absorption.
This paper reports the fabrication and characterization of a novel silver modified buckypaper-carbon fiber/phenol-formaldehyde (SMBP-CF/PF) composite for lightning strike protection (LSP). The composite not only provides electrical protection with the SMBP, but also effectively reduces the lightning strike (LS) damage with the CF/PF layer for thermal insulation. Residual strength rate of the SMBP-CF/PF-CFRP composite maintains 97.25% after the LS test. Compared with commercial materials, the usage of the SMBP-CF/PF composite demonstrates reduced weight as well as the excellent LSP performance. Therefore, the lightweight SMBP-CF/PF composite can be applied as the novel LSP material for aircraft.
Lightning is one of the most important threats to the safe operation of an aircraft. Rotorcraft can experience lightning strikes on the main rotor blades and tail rotor blades which can seriously affect the rotorcraft and its components in several ways. When lightning strikes a rotor blade made of composite material, electrical–thermal multi-physical phenomena such as the Joule heating effect occur. In this study, an electrical-thermal computational simulation of lightning strikes on composite rotor blades was performed. The simulation analyzed various situations including the presence of a lightning protection system on the composite rotor blade. Emphasis was placed on the effects of geometric parameters of expanded metal foil on the lightning protection performance. In addition, the effects of curvature on thermal and electrical response were investigated. The thermally damaged area was found to substantially increase in inner layers compared to the flat plate case.
Carbon nanotubes can be used to protect composites from lightning strike due to their high electrical conductivity. A kind of carbon nanotube film was developed to protect composite structures here. Its lightning strike protection effect was studied. Artificial lightning strike tests were conducted on carbon nanotube film protected specimen, traditional surface silver coating protected specimen and pristine specimen in this paper. Coupled thermal-electrical finite element models were established to study the lightning strike protection effect and damage mechanism of two kinds of methods. Numerical results agree well with experimental ones, illustrating the validity of the models. The results show that lightning strike damage in the carbon nanotube film protected laminate is restricted in 5 composite piles and 5 carbon nanotube films close to the lightning strike surface. Whereas lightning strike damage in surface silver coating protected specimen is restricted in coating and 2 composite piles close to the lightning strike surface. Compared with the pristine laminate, damage in the laminate with carbon nanotube films decreases by 77.6% and 68.0% in area and depth respectively, whereas damage in the laminate with surface silver coating decreases by 66.1% and 92.0% correspondingly. The inserted carbon nanotube films can increase the electrical conductivity and conduct the strike current and energy along both depth and in-plane directions quickly, while surface silver coating mainly conducts the energy along in-plane direction.
The aim of this article is to present a study of the behavior of patch-repaired laminates subjected to low-velocity impacts. A broad range of impact energies was selected. Results for repaired laminates in terms of contact load, damage and absorbed energy were compared to those obtained from intact specimens. At impact energies below 10 J, energy absorption in repaired specimens was higher than the one given in intact laminates, although the measured damage area was found to be greater in the former configuration. For higher impact energies, both damage area and energy absorption in intact specimens were greater than in repaired laminates.
Lightning strike damage in carbon fibre reinforced polymer (CFRP) composites with a lightning strike protection (LSP) system involves complex mechanisms. Few numerical studies simulating lightning strike damage have been developed considering the dielectric breakdown of LSP systems under lightning strike. This study presents a coupled thermal–electrical finite element (FE) model of the evolution of damage in CFRP composites with different advanced LSP systems under lightning strike. The advanced LSP system consists of a buckpaper layer and an adhesive layer. The dielectric breakdown strength of the adhesive layer and CFRP composite is incorporated into the FE model by an ABAQUS subordinate functionality. First, the FE model is utilized to predict damage to a CFRP composite without an LSP system. It is found that the predicted area and depth of damage agree well with the experimental data. Then, the lightning strike damage to CFRP composites with different LSP systems is quantitatively determined by the FE analysis. The results show that, after addressing dielectric breakdown, the FE predictions are comparable with experimental results for various LSP systems.
The damage of carbon fiber reinforced polymer (CFRP) laminated composites under lightning strike is analyzed by coupled electrical-thermal-pyrolytic models, which is implemented by the ABAQUS/Standard finite element code coupled with user-defined subroutines USDFLD and HEATVAL. To clarify the effects of the lightning current waveform parameters and the thermal/electrical properties of CFRPs, the damages of CFRP laminated specimens under diverse lightning current waveforms are experimentally and numerically analyzed. The results reveal that the damage volume shows a strong logarithmic relationship with the action integral, and that the damage is strongly governed by the electrical properties of CFRPs, though thermal conductivity variation barely affects the damage volume.
Carbon fiber reinforced polymers (CFRP) have been increasingly used in aircraft structures. However, their relatively low electrical conductivity leads to the vulnerability to lightning strike. Herein, the carbon nanotube buckypaper-based coatings composed of conductive buckypaper and insulating adhesives were developed to protect the CFRP laminates. Their influence on the lightning strike protection (LSP) effectiveness was systematically studied and the possible mechanisms were discussed. It was demonstrated that the conductive layer of buckypaper could facilitate the lightning current to the ground and dissipate the energy. Moreover, a relatively thick insulating adhesive could hinder the transfer of the lightning current through the thickness direction to CFRP laminates, thus further enhance the LSP effectiveness. An optimized LSP coating developed in this work was composed of a ∼70 μm thick buckypaper and a ∼200 μm thick boron nitride modified epoxy insulating adhesive, which resulted in a weight reduction up to 30% compared to the commercial Cu LSP coating, and could sustain the simulated lightning strike with peak current up to 100 kA.
The high Joule heating of carbon fiber reinforced polymer composites (CFRP) subjected to lightning strike induces resin decomposition and carbon sublimation. The mechanism and characteristics of the change in composite material properties are the key basis of the numerical analysis and the optimal design of composite structures. In order to elucidate the damage phenomena caused by lightning strike, a tightly coupled electrical-thermal-pyrolytic analysis is conducted by introducing the numerical calculation of resin pyrolysis degree on the basis of thermal-electrical numerical analysis. Hence the electrical and thermal properties in both out-plane and in-plane directions are modeled as functions of the pyrolysis degree of the composite material, namely the material properties change with the component during the decomposition, which is revealed to be reasonable from both the numerical and the experimental results. The research is helpful for understanding the complicated relationships in the important damage process including electrical, thermal and chemical phenomena.
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.
Experiments and finite element analysis (FEA) were performed on scarf-patch repaired composite panels. Tensile static tests were performed on pristine and repaired panels to evaluate their tensile strength. The obtained results showed that the repaired panels restored tensile strength by 95% of the pristine value. Subsequently, a verification finite element (FE) model was established. Two additional models, one with homogenized mechanical properties of the laminate and one that considered that the ply-by-ply properties were built to simulate the experimental repairs. The predictions of the two models agreed reasonably well with the experimental results and the optimum scarf angle was found at 2.5°.
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.
To predict the static response of patched plates with circular cutout a full-discrete layer model is proposed. The shape functions are based on 2-D and 1-D integrals of Legendre polynomials, allowing accurate simulation of 3-D behavior. Exact mapping of curved boundary is undertaken using blending functions. The easy to use modeling scheme is applied to single-patch repaired plates with circular cutout and compared with published results. The results of parametric studies on patched plates are presented by varying the relative thicknesses of patch and adhesive, patch shape, and patch size.
Simple analytical and numerical models are proposed to determine the optimum geometry and compressive strength of flush composite repairs. To account for the material nonlinearities and plastic deformation of the adhesive, the average stress failure criterion (ASFC) is used with the finite element stress distributions to estimate the ultimate strength of the three-dimensional repaired configuration. This avoids the need for a nonlinear analysis, thus saving on computation time and memory requirements. The simple scarf-joint analysis underestimates the strength of the scarf patch repair by more than 40% and predicts an optimum scarf angle of 4 deg compared with an angle of almost 7 deg obtained by the ASFC.
This study investigates the thermal degradation and flammability properties of structural epoxy adhesive and carbon/epoxy composite subject to environmental and chemical agents typical of aerospace operations: water, jet fuel, hydraulic fluid, fuel additive (not mixed in jet fuel), at three conditioning temperatures similar to those experienced by an aerospace composite structure during its operation. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) gave results consistent with those from hardness tests on control and conditioned specimens: they provide evidence for the severity of the adhesive’s degradation due to hydraulic fluid (for conditioning temperatures higher than room temperature) or fuel additive (at all temperatures of this study). TGA scans show the thermal degradation of carbon/epoxy composite by fuel additive at room temperature. Through Microscale Combustion Calorimetry (MCC), the flammability properties of selected specimens were measured. Results for the treatment at room temperature confirmed those from the TGA, DSC and hardness tests. The MCC showed a decreased heat release rate for the adhesive samples treated at high temperature in hydraulic fluid and fuel additive. This may be possibly due to the increased amount of char compared to the room temperature treatments. These new results raise concerns regarding the durability of structural epoxy adhesive contaminated by hydraulic fluid or fuel additive, under simplified test conditions (no prior mechanical damage, no coatings/sealants, no mixing of fluids).
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.
Mechanics of the composite repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 85% and 90% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch.
This paper presents the in-plane elastic properties of 2/2 twill weave, T300 carbon/epoxy, woven fabric composite plates, obtained by both finite element analysis and experiments. A micromechanical, three-dimensional (3D) finite element model of the single layer unit cell of a 2/2 twill weave fabric composite is built, and a homogenization process is implemented. A unit cell is chosen such that it encloses the characteristic periodic repeat pattern in the fabric weave. Detailed geometry together with construction procedures for this new model are developed by using ANSYS Parametric Design Language (APDL). In this respect, the scope for altering the weave and yarn parameters is facilitated. Standard tensile and rail shear tests with modifications are performed for this kind of woven fabric composite. Elastic mechanical properties determined by experiments are presented, and the finite element model is verified. Satisfactory correlation between the predicted and experimental results are obtained.
The mechanical and failure behavior of a carbon-fabric/epoxy composite was characterized and appropriate failure criteria in three dimensions were proposed. The material investigated was reinforced with a five-harness satin carbon fiber weave. Test methods were developed/adapted for complete mechanical characterization of textile composites in three dimensions. Through-thickness tensile and compressive properties were obtained by testing short waisted blocks bonded to metal end blocks. The through-thickness shear behavior was determined using a short beam with V-notches under shear. Multiaxial states of stress were investigated by testing in-plane and through-thickness specimens under off-axis tension and compression at various orientations with the in-plane directions. Three types of failure criteria in three dimensions were proposed, limit criteria (maximum stress), fully interactive criteria (Tsai–Hill, Tsai–Wu), and failure mode based and partially interactive criteria (Hashin–Rotem, Sun, NU). The latter, a newly developed interlaminar failure theory, was found to be in excellent agreement with experimental results in the through-thickness direction, especially those involving interlaminar shear and compression.
ARP 5412 Aircraft Lightning Environment and Related Test Waveforms
- S Aerospace
- Aerospace S.
S. Aerospace, ARP 5412 Aircraft Lightning Environment and
Related Test Waveforms, SAE International, London, UK, 2005.
Numerical study on lightning strike protection method for composite rotor blade based on air breakdown and insulating adhesive layer
- K Li
- X Cheng
- Z An
- Li K.
On the impact response of electrified carbon fiber polymer matrix composites: effects of electric current intensity and duration
- R L Sierakowski
- I Y Telitchev
- O I Zhupanska
Sierakowski RL, Telitchev IY, Zhupanska OI. On the impact
response of electrified carbon fiber polymer matrix composites:
effects of electric current intensity and duration. Compos Sci
Technol. 2008;68(3-4):639-649. doi:10.1016/j.compscitech.2007.
09.019
Effect of the electric current on the impact fatigue strength of CFRP composites
- A M Amaro
- Pnb Reis
- J Santos
- M Santos
- M A Neto
Amaro AM, Reis PNB, Santos J, Santos M, Neto MA. Effect of
the electric current on the impact fatigue strength of CFRP
composites. Compos Struct. 2017;182:191-198. doi:10.1016/j.
compstruct.2017.09.032
Avaliação das características da Resina ep oxi Com Diferentes Aditivos Desaerantes
- A Oliveira
- Cristiane Miotto
- Sandro Campos Becker
- Amico
Oliveira A. Cristiane Miotto Becker, Sandro Campos Amico.
Avaliação das características da Resina ep oxi Com Diferentes
Aditivos Desaerantes. 2015;25(2):186-191. doi:10.1590/0104-1428.1661