复合材料雷击防护电热耦合模型

为了研究复合材料雷击防护(lightning strike protection,LSP)系统在雷电流作用下的损伤规律,基于雷击过程中的能量守恒关系,建立复合材料层合板雷击防护的电-热耦合数学模型。在此基础上,在ABAQUS中建立铝涂层防护的碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)层合板雷击烧蚀损伤有限元模型,并对雷击烧蚀损伤进行分析,和实验结果对比验证仿真的有效性,得出复合材料层合板在不同峰值雷电流、不同组合波形和不同铝涂层厚度雷电流作用下的烧蚀损伤规律。结果表明:铝涂层厚度相同时,峰值电流从50kA 增大到100kA时,复合材料层合板损伤面积约增大 1.5 倍;10/350波形50 kA峰值雷电流作用下,基准件的损伤面积约为0.05 mm厚度铝涂层防护系统下复合材料损伤面积的4倍。     

基于热力耦合层合板雷击损伤特性分析

为研究复合材料层合板在雷电流作用下的烧蚀损伤力学特性,建立复合材料雷击热力耦合有限元分析模型,与文献实验结果对比验证模型的有效性。根据Hashin三维失效准则编写用户材料子程序,分别得出层合板雷击烧蚀区域周围出现的力学损伤、各层力学损伤分布以及首层在不同方向上的应力分布,分析得出层合板的烧蚀损伤随雷电流持续时间的变化规律。结果表明:由于存在较高的温度梯度,导致层合板出现较大的热膨胀应力,进而导致层合板内部产生各种力学损伤,即基体开裂、分层及纤维断裂;雷击电流施加时间、峰值电流与温度场均对层合板烧蚀面积产生较大的影响。     

复合材料层合板雷击烧蚀损伤模拟

 为解决复合材料层合板的雷击烧蚀问题,通过复合材料层合板雷电流烧蚀的热-电-结构耦合分析,建立复合材料层合板烧蚀的三维有限元模型。利用删除单元法模拟复合材料层合板在不同脉冲波形雷电流作用下的冲击响应,进行复合材料层合板雷击损伤机理和损伤模式分析,得出了复合材料层合板在不同脉冲波形和峰值雷电流作用下的瞬态热传递和热烧蚀规律。分析了不同雷电流参数对烧蚀结果的影响。结果表明峰值电流、放电量和比能对复合材料层合板的烧蚀尺寸和内部损伤产生很大的影响。     

CFRP层合板雷击烧蚀损伤模拟的电流加载方式分析

通过改进加载方式减小数值模拟与试验结果误差对于提高仿真准确性具有一定意义。本文探究复合材料层合板在不同形式雷击电流下的烧蚀损伤特性，改进Braginskii 电弧半径扩展公式，建立适用于雷击过程的电弧扩展半径数值模型；基于ABAQUS 建立CFRP 层合板有限元模型，分析不同电流加载方式下的烧蚀损伤情况。结果表明：建立的有限元模型能够模拟CFRP 层合板雷击烧蚀损伤；扩展移动加载造成的损伤面积、损伤深度和损伤体积与试验结果对比误差均约为7%，较其他加载方式仿真结果与试验结果对比具有良好的一致性，模拟复合材料雷击烧蚀损伤时应同时考虑电流扩展和移动的影响。     

不同喷铝参数对复合材料雷击防护性能模拟

为了研究复合材料不同的雷击防护(lightning strike protection,LSP)系统在雷电流作用下的损伤规律,对雷击损伤过程和烧蚀机理进行分析,建立复合材料层合板雷击防护的能量平衡数学模型。在此基础上,在ABAQUS中建立复合材料基准件、全喷铝和局部喷铝防护系统的碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)层合板电-热耦合有限元模型,和实验结果对比验证模型的有效性,对雷击烧蚀损伤特征进行分析,并引入雷击烧蚀损伤指数DI,得出三种不同模型在不同铝涂层厚度、不同峰值雷电流作用下的烧蚀损伤规律,并对两种不同的局部喷铝防护系统下复合材料的损伤特征进行对比分析。结果表明:雷击防护系统下复合材料的烧蚀损伤面积和铝涂层厚度关系进行函数拟合,两者均满足幂函数关系。     

碳纤维复合材料基体改性/铜网组合雷击防护性能的研究

传统碳纤维复合材料（CFRP）树脂基体导电性差易遭受雷击损伤,本文使用石墨烯-镀镍碳纤维粉作为导电填料,对树脂基体进行电导率改性,并在表面铺设铜网,进行模拟雷电流冲击试验,检验基体改性/铜网组合雷击防护效果。试验结果表明,树脂基体改性后CFRP层压板在0°、90°纤维方向及厚度方向电导率分别为1.1571×10⁴、1.0871×10⁴、204.2 S/m,分别提高1.54倍、1.16倍、433.47倍。200 kA模拟雷电流A波冲击下,无防护试件雷击附着后明火燃烧,次生效应持续,而单一铜网防护和组合防护则能抑制次生效应;无防护表面最大损伤直径14.62 cm,此能量下铜网被击穿,单一铜网防护表面最大损伤直径19.05 cm,而组合防护表面最大损伤直径8.93 cm,下降53.12%;相比无防护试件,单一铜网和组合防护内部损伤面积分别下降66.2%和96.7%。单一铜网击穿后,树脂烧蚀后产生汽化反冲,增大损伤铜网脱落面积;组合防护铜网击穿后,改性树脂迅速导走电流,减小铜网脱落和内部烧蚀面积。     

Z-pin增强树脂基复合材料单搭接接头抗冲击性能

为了研究Z-pin增强树脂基复合材料接头的抗冲击性能,制备了Z-pin增强单搭接接头冲击试样。对比不同树脂体系Z-pin/层合板界面裂纹扩展,分别通过Z-pin拔脱试验和接头剪切试验研究Z-pin冲击后拔脱强度和单搭接接头冲击后剪切强度;结合有限元模拟和超声C扫描研究搭接面分层损伤情况。结果表明,相同冲击能量下,环氧Z-pin/环氧层合板界面抗冲击性更强,冲击能量越大,裂纹扩展越显著;Z-pin增强树脂基复合材料显著减小分层损伤面积,提高冲击后剪切强度,体积分数为1.5%、直径为0.5mm的Z-pin增强层合板分层损伤面积仅为40%,冲击后剪切强度的下降率仅为24.89%。随着Z-pin体积分数增加,搭接面损伤面积逐渐减小,冲击后剪切强度先增加后降低;随着Z-pin直径增加,层间损伤面积增加,冲击后剪切强度逐渐降低。Z-pin增强接头分层损伤模型模拟结果与试验结果基本吻合。      

碳纤维复合材料电导率改性与抗雷击性能

传统碳纤维复合材料(CFRP)中的树脂基体电阻率大,在强电流下会产生大量阻性热从而造成损伤,增强其电导率能够有效提高CFRP的雷击防护性能。在树脂基体中添加银粉颗粒进行电导率改性,通过有限元仿真分析银粉含量对雷击防护性能影响,确定CFRP基体中的最佳银粉含量为38%。沿厚度方向电导率的改性效果最佳,提高了217.3倍。使用不同峰值的D波形雷电流对改性CFRP层压板进行模拟雷击实验,并对未改性以及表面铺设铜网的层压板进行相同能级的对照实验,通过目视损伤观察和透视超声扫描比较损伤特征和损伤面积,评估基体改性CFRP的抗雷击性能。结果表明:基体改性可以阻碍表面铺层被击穿,降低纤维断裂翘曲以及分层损伤;峰值电流20 kA、40 kA和60 kA下,铜网防护能使雷击透视损伤面积分别下降100%、86.61%和37.46%,基体改性整体防护能使雷击透视损伤面积分别下降84.02%、81.03%和40.91%。     

含铜网复合材料雷电流直接效应实验研究

为了研究铜网防护层对复合材料的雷击防护效果,采用两种不同雷电流波形,对不同尺寸含铜网(0.25 mm厚)与无铜网防护复合材料试件进行模拟雷电流冲击实验,通过目视损伤观察、光学显微镜放大、超声损伤扫描,对比分析复合材料的雷击损伤程度及特征。结果表明:雷电流波形1,峰值电流分别为50 k A和80 k A时,Type1(150 mm×100 mm)型试件无铜网防护下复合材料的雷击损伤面积和深度分别为1785 mm~2,0.63 mm和3041 mm~2,0.96 mm,而含铜网防护试件基本无损伤;雷电流波形2,峰值电流为40 k A时,Type 2(250 mm×45 mm)型试件无铜网防护下的雷击损伤面积和深度分别为2156.75 mm~2,0.36 mm,而含铜网防护试件损伤面积小于100 mm~2,里层还未损伤;0.25 mm铜网能够承受的最大雷电流强度存在一个门槛值,该门槛值可用作用积分来表示,雷击防护效果与试件尺寸无关,仅与作用积分有关,其对应作用积分门槛值约为85218 A~2·s。     

缝纫对复合材料层合板强度和抗冲击性能的影响

主要研究了缝纫对复合材料层合板的强度和抗冲击性能的影响。通过对不同缝纫密度、缝纫方向、缝线材料和缝线直径的试件进行试验研究 ,分析了缝纫参数对层合板的压缩强度、层间剪切强度、断裂韧性 GIC和 GIIC、低速冲击损伤以及冲击后压缩 ( CAI)强度的影响。结果表明 :缝纫使层合板的 GIC和 GIIC有明显提高 ;随缝纫密度的增大 ,层间剪切强度和 CAI强度有显著提高 ,冲击分层损伤面积有一定程度的减小 ;但它们与缝线的直径关系不大。     

基于复合材料分层损伤模型的层压板静强度分析

对层压板进行强度分析时同时考虑面内失效和分层损伤可以得到更加合理的强度预测值。基于复合材料层压板分层机理分别采用Hashin准则和分层因子进行面内损伤和分层损伤的计算,并结合材料性能退化发展了一种能够考虑分层损伤的层压板累积损伤模型。该模型能够模拟层压板面内和分层损伤产生、发展直至最终破坏的完整过程。通过对两种典型复合材料层压板单钉连接接头的失效分析,表明计算结果与传统三维有限元计算结果相比精度较高,并能有效预测各层间分层损伤的扩展情况。     

Carbon nanotube protected composite laminate subjected to lightning strike: Interlaminar film distribution investigation

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.     

Improving Mode II delamination resistance of curved CFRP laminates by a Pre-Hole Z-pinning (PHZ) process

This paper presents an experimental investigation of the Mode II delamination resistance of curved CFRP laminates reinforced with Z-pins. A Pre-Hole Z-pinning (PHZ) process is developed to reduce the in-plane damage of the Z-pinned laminates. The microstructural observation of the Z-pinned laminate specimens indicates that the PHZ process can effectively decrease the defects including the Z-pin offset angle and the area of eyelet zone. The influences of the volume fraction and diameter of Z-pin on the fracture toughness and the delamination crack growth rate of the specimens under End Notch Flexure (ENF) loading are then determined experimentally. The test results show that Z-pin increases the interlayer stiffness of the laminate. The delamination crack growth rate is reduced with the increase of Z-pin diameter and volume fraction, and a reduction up to 40% is achieved compared with the specimens without pins. Furthermore, the Mode II fracture toughness is significantly improved with the increase of Z-pin volume fraction. When Z-pin volume fraction increases by 1%, the achieved fracture toughness is about 200% higher compared to the unpinned laminates.     

Thermal damage analysis of aircraft composite laminate suffered from lightning swept stroke and arc propagation

Lightning strike is a complicated process involving multi-field coupling. In order to investigate the thermal damage mechanism of carbon fiber reinforced composites subject to lightning swept stroke, a complete numerical method is presented. Numerical model of lightning discharge is established based on Magneto Hydro Dynamics (MHD) and calculated by FLUENT secondary development technology. Considering aerodynamic flow effect, channel formation and evolution process during lightning discharge is analyzed for lightning current waveform A. Thermal-electric Coupling model is presented according to Radial Basis Function (RBF) interpolation theory, which is implemented by compiling program to make lightning current and heat energy inject into composite laminate. Consequently, damage mechanism of composite laminate under lightning swept stroke is studied based on the coupled numerical model and element deletion method. Ablation damage morphology of composite laminate is analyzed to understand plasma expansion and reattachment in arc root. The results show that aerodynamic flow makes the lightning channel move fast and composite laminate is deteriorated due to thermal damage.     

Analysis of composite laminates with intra- and interlaminar damage

Failure process of composite laminate under quasi-static or fatigue loading involves sequential accumulation of intra- and interlaminar damage. Matrix cracking parallel to the fibres in the off-axis plies is the first intralaminar damage mode observed. These cracks are either arrested at the interface or cause interlaminar damage (delamination) due to high interlaminar stresses at the ply interface. This paper summarises recent theoretical modelling developed by the authors on stiffness property degradation and mechanical behaviour of general symmetric laminates with off-axis ply cracks and crack-induced delaminations. Closed-form analytical expressions are derived for Mode I, Mode II and the total strain energy release rates associated with these damage modes. Dependence of strain energy release rates on crack density, delamination area and ply orientation angle in balanced and unbalanced symmetric laminates is examined and discussed. Also, stiffness degradation due to various types of damage is predicted and analysed.