含紧固件复合材料层压板结构雷击烧蚀损伤特征分析

为了对含紧固件复合材料层压板的雷击烧蚀损伤特征进行分析,根据雷击过程中的能量平衡关系,建立了含紧固件复合材料层压板结构雷击烧蚀损伤数学分析模型。基于该分析模型,在ABAQUS中建立了含紧固件复合材料层压板结构雷击烧蚀损伤分析三维有限元模型,并对不同电势边界条件下的雷击烧蚀损伤进行了分析。分析结果表明:由于金属紧固件的存在,雷电流可以通过紧固件沿层压板结构厚度方向传导,然后在各铺层内进行电流分配,各方向铺层传导雷电流的能力与该层电势梯度方向和电势梯度方向的电导率有关;在不同的电势边界条件下,各层的电势分布有所差异,从而导致了各铺层传导雷电流能力的不同,最终引起不同的雷击烧蚀损伤分布。通过本文的研究,能够对含紧固件复合材料层压板结构的雷击烧蚀损伤特征有定性的认识。     

含雷击热-力耦合损伤复合材料层压板拉伸剩余强度预测

为了对含雷击热-力耦合损伤复合材料层压板的剩余强度进行预测,基于连续介质损伤力学法(CDM)和唯象分析法,建立了表征复合材料雷击热-力耦合损伤的刚度矩阵渐进损伤退化模型。基于该模型,通过ABAQUS有限元仿真软件,建立了含雷击热-力耦合损伤的复合材料层压板结构三维模型。结合UMAT子程序,完成了拉伸载荷下的剩余强度预测。结果表明:通过与试验对比,仿真结果与试验结果取得了良好的一致性。本文所建立模型,能够有效进行含雷击热-力耦合损伤复合材料层压板结构拉伸剩余强度预测。     

含紧固件碳纤维增强树脂复合材料在雷电流A分量下的损伤特性

为深入分析雷电环境下含紧固件碳纤维增强树脂（CFRP）复合材料的损伤机制及尺寸对损伤面积的影响规律,对两种不同尺寸含紧固件CFRP进行雷电损伤试验和仿真研究。根据热电耦合理论在ABAQUS中建立含紧固件CFRP的热-电耦合模型,得到单一雷电流A分量作用下CFRP的温度场分布规律;雷电损伤试验中采用超声C扫描方法评估试件损伤特性。试验和仿真结果表明:此雷击条件下,雷电流通过紧固件扩散到CFRP层合板整个厚度,试件在雷电流峰值不太大的情况下损伤面积较小,但随电流峰值的增大,损伤面积剧增、分层损伤严重。电流相近情况下不同尺寸的含紧固件CFRP的损伤分层、损伤形态及面积相近,尺寸对试件的损伤特性影响较小。试验和仿真研究为CFRP的结构设计提供一定的仿真和试验数据支撑。      

雷电流组合波形下碳纤维/环氧树脂基复合材料层压板雷击损伤试验

为了评估碳纤维/环氧树脂基复合材料位于不同飞机雷击分区下的雷击损伤程度及损伤特征,采用A+B、D+B+C和A+B+C+D 3种不同的雷电流波形组合,对两类不同尺寸复合材料层压板试验件（Type1和Type2）进行了模拟雷电流冲击试验,通过目视损伤观察和超声损伤扫描,分析评估了复合材料位于飞机1A区、2A区及1B区时的雷击损伤程度及特征,同时还对含铜网防护碳纤维/环氧树脂基复合材料层压板在不同雷击分区下的雷击防护效果进行了评估。结果表明：不同雷击分区下,碳纤维/环氧树脂基复合材料在雷电流作用下的损伤模式基本一致,包括纤维断裂、基体烧蚀及分层损伤;对于相同类型试验件,1B区对应雷击损伤程度最严重,其次为2A区,1A区损伤程度最小;在相同雷击分区下,长宽比较小的Type1型试验件雷击损伤程度大于长宽比较大的Type2型试验件;0.25 mm厚铜网能够有效对碳纤维/环氧树脂基复合材料进行雷击防护,位于1A区、2A区及1B区的含防护与无防护Type2型试件,前者雷击损伤程度较后者分别下降88.9%、53.9%和68.7%。     

碳纤维蜂窝夹层结构防雷击铜网胶膜共固化设计及雷击与承载能力试验

为有效防止直升机碳纤维蜂窝夹层复合材料蒙皮在雷击环境遭受雷击损伤,采用在蜂窝夹层结构表面铺设铜网胶膜一次固化成形的方法预防。针对直升机不同雷电附着区的七种典型蜂窝夹层结构采用A+B+C+D和D+B+C两种雷电流试验波形进行雷电直接效应试验,并采用面内剪切试验对试验件雷击前/后承载能力和铜网胶膜对承载能力的影响进行试验对比分析。试验证明,在蜂窝夹层结构表面铺设铜网胶膜一次固化成形的方法,能够有效预防雷击损伤,试验件未出现基体大面积烧蚀、分层和片状剥落等现象;承载能力试验中蜂窝夹层结构表现沿载荷加载方向起皱破坏的模式;试验件在雷击前/后承载能力衰减不明显,最大衰减量为4.5%;铜网胶膜有助于提高试验件承载能力,C型试验件相比H型试验件承载能力提高了26.9%;试验件承载能力分散性相对较小,最大分散度为10.4%。     

碳纤维增强树脂复合材料在多重连续雷电流冲击下的损伤特性

通过对比碳纤维增强树脂复合材料（CF/EP）层合板在单一雷电流脉冲及不同组合及时序的多重雷电流分量作用下的雷击损伤特性,探索多重连续雷电流分量在CF/EP层合板上的散流过程与作用机制。研究发现CF/EP层合板在雷电流脉冲作用下出现纤维断裂、烧蚀、树脂热解、铺层分离等严重雷击损伤。在雷电流A、B、C及D分量连续作用下,CF/EP损伤面积达到2 790 mm2,损伤深度约1.28 mm。在多重连续雷电流脉冲作用下,CF/EP的雷电损伤深度主要与雷电流A、B及D分量的冲击力效应及介质击穿效应有关,而持续时间长、转移电荷量大的雷电流C分量的热效应对损伤面积的贡献接近40%。CF/EP层合板雷击损伤特性与雷电流分量的组合及作用时序关系密切,雷电流分量单独作用时造成的CF/EP雷击损伤效果与处于多重连续脉冲序列中时所造成的雷击损伤效果有很大差异。对CF/EP在多重连续雷电流作用下损伤效应的研究能够加深对雷电作用过程的理解,并为CF/EP雷电直接效应机制研究及试验方法的建立及完善提供实验和理论依据。      

金属裂纹板复合材料胶接修补强度的弹塑性有限元预测

金属裂纹板经复合材料补片胶接修补后,其结构强度明显提高,但裂纹板中的裂纹会导致严重的应力集中现象,并易产生塑性变形,呈现强烈的材料物理非线性特性,需要采用弹塑性力学原理,进行复合材料胶接修复结构的静强度预测。为此,考虑金属板材料的非线性特性,建立了金属裂纹板复合材料胶接修补结构的弹塑性有限元模型,并通过试验验证了模型的有效性。在此基础上,提出了基于裂纹尖端的张开位移(COD)判据的拉伸强度预测方法,分析了修复结构的塑性应变、COD以及静拉伸强度。结果表明:相对于应力强度因子K判据, COD判据能更有效地预测修复试件的静拉伸强度。      

“离位”增韧复合材料准静态压入损伤特性研究

采用"离位"增韧技术对双马来酰亚胺复合材料层压板进行了层间增韧,然后对增韧和未增韧的两种双马复合材料层压板进行准静态压入及冲击后压缩剩余强度试验研究,并用超声C扫描和热揭层对层压板的损伤进行测量。结果表明:经过"离位"增韧的双马复合材料层压板层间形成了热塑性树脂/热固性树脂双连续的结构,该结构不仅能抑制增韧层压板的内部损伤面积,改善损伤阻抗,使其表面凹坑深度更明显,而且还大幅提高了其损伤容限。     

复合材料层压板抗冲击行为及表征方法的实验研究

对14种复合材料体系约800个试样进行了冲击阻抗和含损伤层压板压缩强度试验研究,研究发现对于同一种复合材料层压板的冲击能量-凹坑深度曲线和凹坑深度-压缩破坏应变曲线均存在拐点,在出现拐点后内部的分层损伤叠加面积基本不再增加,压缩剩余强度基本不再降低,表面冲击部位开始出现纤维断裂。研究表明,采用传统CAI来表征损伤容限性能的方法可能得到与实际结构损伤容限特性相反的结论。因此,提出了利用拐点附近特性来表征复合材料层压板的抗冲击行为（包括损伤阻抗和损伤容限）的建议,即分别采用QSI方法得到的准各向同性层压板的最大接触力F_max和压缩破坏强度（应变）的门槛值CAIT来表征复合材料层压板的损伤阻抗和损伤容限行为。      

碳纤维增强银粉改性树脂复合材料的雷击损伤效应

针对碳纤维增强树脂(CFRP)复合材料中树脂电阻大,在雷电流作用下会产生大量焦耳热造成雷击损伤的短板,探索通过增强基体的导电性来解决这一问题。为实现对CFRP复合材料的改性,在其环氧树脂浆料中加入了以Ag粉为主的导电填料,使改性CFRP复合材料层合板沿厚度方向的电导率提高217.30倍。采用不同峰值的单一雷电流D分量分别对改性及未改性CFRP复合材料层合板试件进行雷击损伤实验,通过损伤区域超声C扫描图像、试件残余温度场和仿真热解损伤的对比,分析基体改性对CFRP复合材料雷击损伤的防护机制。结果表明:通过Ag粉改性能有效提高CFRP复合材料层合板的电导率,且在厚度方向上的改性效果最佳;在峰值电流分别为20 kA、40 kA和60 kA的条件下,改性CFRP复合材料层合板的损伤面积分别下降87.28%、77.82%和88.59%,损伤深度分别增加147.06%、130.65%和119.72%;以损伤体积为最终指标,则Ag粉改性基体能有效降低CFRP复合材料的雷击损伤,其防护机制是通过减少雷电流作用下的高温区域面积和升温幅度来降低热解和爆炸冲击实现。      

Lightning Strike Ablation Damage Characteristic Analysis for Carbon Fiber/Epoxy Composite Laminate with Fastener

In order to analyze the lightning strike ablation damage characteristic of composite laminate with fastener, based on the energy-balance relationship in lightning strike, mathematical analysis model of ablation damage of composite laminate with fastener was constructed. According to the model, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate with fastener suffered from lightning current was established based on ABAQUS, and lightning strike ablation damage characteristic was analyzed. Analytical results reveal that lightning current could conduct through the thickness direction of the laminate due to the existence of metallic fastener, and then distribute to all layers, finally conducted in-the-plane of each layer, conductive ability of different layup orientations depend on potential distribution and in-the-plane electrical conductivity along potential gradient declining direction; different potential boundaries correspond to different potential distribution in each layer, and result in conductive ability of different layup orientations was changed, then caused different lightning strike ablation damage distribution. According to the investigation in this paper, we can recognize the lightning strike ablation damage characteristic of composite laminate with fastener qualitatively.     

雷击冲击力作用下复合材料层合板动力学响应及损伤特性

采用基于连续介质损伤理论（CDM）的复合材料三维渐进损伤分析模型,以ABAQUS有限元分析软件为平台,结合VUMAT子程序,对雷击冲击力作用下的复合材料层合板进行了三维动力学分析,研究了雷击冲击力作用下层合板的动力学响应及损伤特性。结果表明,在雷击冲击力作用下,层合板做降幅振荡运动,冲击力做功与层合板内能和动能相互转换,同时伴随着黏性耗散能,冲击力做功大小可用雷电流库伦量与作用积分的函数表示;层合板损伤由外力做功大小决定,对于同种材料,基体、纤维及分层损伤分别存在不同的损伤能量临界值,当冲击力做功大于该值,层合板会产生对应的损伤;在相同边界支持条件下,冲击力总功最大值决定了不同损伤类型损伤状态变量的大小,与波形参数和峰值电流无关。     

Lightning Strike Ablation Damage Influence Factors Analysis of Carbon Fiber/Epoxy Composite Based on Coupled Electrical-Thermal Simulation

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.     

Experimental and Numerical Simulation Analysis of Typical Carbon Woven Fabric/Epoxy Laminates Subjected to Lightning Strike

To clarify the evolution of damage for typical carbon woven fabric/epoxy laminates exposed to lightning strike, artificial lightning testing on carbon woven fabric/epoxy laminates were conducted, damage was assessed using visual inspection and damage peeling approaches. Relationships between damage size and action integral were also elucidated. Results showed that damage appearance of carbon woven fabric/epoxy laminate presents circular distribution, and center of the circle located at the lightning attachment point approximately, there exist no damage projected area dislocations for different layers, visual damage territory represents maximum damage scope; visible damage can be categorized into five modes: resin ablation, fiber fracture and sublimation, delamination, ablation scallops and block-shaped ply-lift; delamination damage due to resin pyrolysis and internal pressure exist obvious distinguish; project area of total damage is linear with action integral for the same type specimens, that of resin ablation damage is linear with action integral, but no correlation with specimen type, for all specimens, damage depth is linear with logarithm of action integral. The coupled thermal–electrical model constructed is capable to simulate the ablation damage for carbon woven fabric/epoxy laminates exposed to simulated lightning current through experimental verification.     

Lightning ablation suppression of aircraft carbon/epoxy composite laminates by metal mesh

Three-dimensional finite element (FE) models of carbon/epoxy composite laminates with copper mesh and aluminum mesh protection were established subjected to lightning strike, in which different mesh spacing was selected. Effectiveness of numerical method was verified and impulse current waveforms with different current peaks were applied according to aircraft lightning zones. Thermal-electrical material parameters varying with temperature were added into numerical models. Element deletion method was used to deal with lightning ablation elements of composite structures. The results show that ablation area and depth of composite laminates with metal mesh protection are significantly smaller, which proves good protection effectiveness of metal meshes on anti-lightning strike. The denser the mesh spacing, the better the anti-lightning strike will be. Protection of composite laminates with copper mesh has better effects than that of aluminum mesh. Considering the effect of mesh spacing variation on composite structural weight and anti-lightning strike, the ideal mesh spacing was obtained.     

Artificial lightning testing on graphite/epoxy composite laminate

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.     

Damage resistance and tolerance of carbon/epoxy composite coupons subjected to simulated lightning strike

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.