铺层顺序对复合材料薄壁圆管轴向压溃吸能特性的影响研究

采用仿真和试验相结合的方法探讨复合材料薄壁圆管在准静态轴向压缩载荷下的失效吸能特性和吸能机理。首先,建立复合材料薄壁圆管"层合壳"有限元模型,通过显式动力学方法求解其在准静态轴向载荷下的压溃失效力学行为。仿真与试验结果在圆管轴向压溃变形过程、初始峰值载荷、平均压溃载荷及比吸能等主要吸能参数上具有很好的一致性,验证了"层合壳"复合材料圆管有限元模型和建模方法的有效性。其次,采用解析模型与仿真分析方法分别对[0/90]_3s、[0/90/0₂/90₂]_s、[0₃/90₃]_s三种不同铺层顺序的复合材料圆管的屈曲载荷与吸能特性进行了对比,进一步分析了铺层顺序对圆管失效吸能特性的影响。研究表明,0°与90°铺层交替程度对复合材料圆管的吸能特性影响较大,保证纤维失效方式在结构宏观失效中占主导地位能够提高材料失效吸收能量。     

含电路模拟结构吸波复合材料

研究了电路模拟结构材质、电路模拟结构尺寸、介质层电磁参数等对电阻渐变型和"陷阱"式结构吸波复合材料的吸波性能和力学性能的影响。结果表明:通过合理的结构设计,在其它条件相同的情况下含电路模拟结构电阻渐变吸波复合材料的吸波性能在8~18 GHz范围内有3~5 dB的提高;含电路模拟结构"陷阱"式吸波复合材料在厚度≤4 mm条件下,实现了吸波性能在8~18 GHz频率范围内吸收率≥12 dB。在提高吸波复合材料吸波性能的同时,电路模拟结构的引入使复合材料力学性能有一定的提高,有利于实现吸波复合材料的吸波/承载一体化。      

结构吸波复合材料透波层的研究

采用弓形法测试反射率,研究透波层的厚度、材质对结构吸波复合材料电磁性能的影响。结果显示,在4~18GHz范围内,厚度对其吸波性能具有显著影响,厚度分别为0.25、0.50和1.25mm的透波层,其结构吸波复合材料的最大吸收峰分别为-37.03,-33.45和-33.22dB;随厚度的增加,吸收峰的位置随向低频段显著漂移,-10dB的有效吸收带宽也显著变窄,分别为11.5,11和6.5GHz;与厚度相比,材质对结构吸波复合材料电磁性能影响较小。     

电路模拟结构在结构吸波材料中的应用探索研究

研究了电路模拟结构(电路屏)在结构吸波复合材料中应用的可行性。重点研究了电路屏结构尺寸、电路屏所处位置及复合材料体系各层中吸收剂配比对吸波特性的影响，结果表明，电路屏在雷达吸波材料中起到了以下的作用：电路屏能引起入射电磁波与反射电磁波的干涉，起到又一反射屏的作用；电路屏的加入能增大吸波结构的表面输入阻抗。通过合理的设计电路屏及使电路屏结构尺寸与吸波结构中的介质层相匹配，电路模拟结构可以有效地提高吸波结构的吸波性能。     

三维编织技术和三维编织复合材料

与层合复合材料相比，三维编织复合材料具有完全整体、不分层的结构，可用于制造结构制件和高功能制件，所以，进一步研究三维编织技术和三维编织复合材料对发展我国新材料具有重要的意义。     

“超材料”结构吸波复合材料技术研究

研究了"超材料"结构吸波复合材料的制备技术及其力学性能与电性能。通过突破不同尺寸金属周期结构单元制备、金属周期结构单元转移、含金属周期结构单元吸波复合材料工艺参数优化等关键技术,制备出电性能和力学性能批次间稳定性良好的含多层金属周期结构单元的"超材料"结构吸波复合材料,"超材料"结构吸波复合材料在2~18GHz频率范围具有宽频高吸收的特性。     

引发角对碳纤维/环氧复合材料圆管件轴向压溃性能的影响

研究了碳纤维增强高韧环氧树脂5288复合材料薄壁圆管件的轴向压溃行为和引发角尺寸之间的关系.对15°,45°,60°引发角的相同尺寸试件分别进行轴向压溃试验,记录了试验过程中的结构载荷力-位移曲线,对照各组不同引发角的管形件轴向压溃过程的峰值压溃载荷、最小压溃载荷后发现,当引发角为60°时,结构的峰值压溃载荷最高,最小压溃载荷最低.对试验件失效后组织进行微观分析后发现,对应于不同引发角,由于接触状态不同,圆管件发生了不同方式的压溃失效,导致了结构吸能力-位移曲线的变化.     

引发机制对复合材料波形梁吸能性能的影响及其破坏形貌分析

复合材料正弦波形梁作为复合材料结构2功能一体化的典型构件 , 在结构高强、 高刚和稳定的前提下 ,其压溃峰值应力和稳态损毁吸能行为是设计结构件的关键性能指标 , 而这两个指标与梁的引发机制密切相关。本文中设计了根部打孔削弱机制、 根部预埋倒角机制、 根部非对称梯度削弱和根部对称梯度削弱机制等 3 种不同引发机制 , 通过对正弦波形梁的静态压溃实验及对压溃梁的宏观和微观形貌分析 , 发现引发机制对正弦波形梁的失效引发和稳态损毁模式影响很大 , 根部预埋倒角正弦波形梁的失效引发和稳态损毁吸能效果最好。     

含电路模拟结构陷阱式吸波复合材料研究

研究了电路屏材质、电路屏尺寸、介质层电磁参数等对“陷阱”式结构吸波复合材料吸波性能的影响,总结了改变参数后吸波性能的变化规律。研究结果表明：通过合理的结构设计,使得吸波复合材料的吸波／承载综合性能得以提高。     

三维编织多功能结构复合材料的发展

在某些实际应用中,需要复合材料不仅具有多种功能,例如抗烧蚀、抗冲击、隔热等,而且还能作为结构材料使用,这种复合材料可以称为多功能结构复合材料.在多功能结构复合材料设计中需要按不同的功能应用和力学特性进行分层设计.利用三维编织技术可以实现多功能结构复合材料的分层异形整体编织,为多功能结构复合材料的发展提供了可能性.本文介绍了三维编织复合材料的性能和制作多功能结构复合材料所采用的三维编织技术.      

Design of Emergency Aircraft Repairs Using Composite Patches

The increasing demand for fatigue life extension of both military and civilian aircraft has led to advances in repair technology for cracked metallic structures. Conventional structural repairs may significantly degrade the aircraft fatigue life and lower its aerodynamic performance. Adhesively bonded composite reinforcement is a new technology of great importance due to the remarkable advantages obtained, such as mechanical efficiency and repair time and cost reduction. In this article, bonded composite patch repairs were designed for quick application to aircraft under emergency conditions, such as aircraft battle damage repair (ABDR). A formulated method was developed, to be applied when damage has to be restored quickly, without restrictions to safety of flight. Different damage cases were investigated using finite-element analysis (FEA), taking into account specific parameters of the structure under repair. Based on the FEA results, a quick design procedure using composite patch repairs for the most frequent damage cases is proposed.     

Global behaviour of a composite stiffened panel in buckling. Part 1: Numerical modelling

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage. A representative panel of a composite fuselage to be tested in buckling is studied numerically.     

基于光纤传感网络的复合材料结构的损伤定位评估方法

提出了利用埋入正交塑料光纤传感网络对飞机复合材料结构的损伤进行定位评估的一种方法。结果表明：利用该方法可以迅速而准确地判断出复合材料结构是否遭到了损伤以及损伤的位置,即对复合材料结构进行损伤定位评估,实现在线实时监控。     

金属纤维钩织复合结构压缩行为分析

目的 针对金属薄壁复合管在轴向压缩时初始峰值载荷高、吸能效果不佳、结构耐撞性不好等问题,研究金属纤维钩织复合结构以及填充6063铝合金管试件的轴向准静态压缩行为和吸能特性。方法 利用短针钩织与烧结工艺制备不同孔隙率的金属纤维钩织结构,将它们填充到6063薄壁管之后,在万能试验机上进行轴向压缩试验,引入评价指标,对试验数据进行处理分析。结果 孔隙率为85.9%、87.9%、89.4%的金属纤维钩织结构的初始峰值力分别为0.48、0.38、0.32 kN,平均压缩力分别为0.72、0.55、0.45 kN。它们的初始峰值力和平均压缩力都非常小,都小于0.8kN。然而,它们的压缩力效率非常高,分别为1.5、1.45、1.41。初始峰值力、平均压缩力和压缩力效率均随孔隙率的增加而减小。这一特性有利于提高结构的耐撞性,表明不存在初始冲击效应,能够直接进入吸能阶段。结论 通过填充金属纤维钩织结构,可以在初始峰值力几乎没有增加的情况下提高6063管材的准静态耐撞性。此外,钩织结构孔隙率对金属纤维钩织结构的准静态力学行为有明显影响。     

Composite sandwich structures with nested inserts for energy absorption application

Polymer composite sandwich structures are promising candidate structures for reducing vehicle mass, thereby improving the fuel economics. Nonetheless, to fully explore this material as the primary structure and energy absorber in vehicles, it is important to understand the energy absorption capability of this material. Hence, in the present work, comprehensive experimental investigation on the response of composite sandwich structures to quasi-static compression has been carried out. The crashworthiness parameters, namely the peak force, absorbed crash energy, specific absorbed energy, average crushing force and crush force efficiency of various types of composite sandwich structures were investigated in a series of edgewise axial compression tests. The tested composite sandwich specimens were fabricated from glass and carbon fiber with epoxy resin. Four distinct modes of failure were observed and recorded. The primary mode of failure observed was progressive crushing with high energy absorption capability. The optimized design in this study had a specific energy absorption capability of 47.1 kJ/kg with a good crush force efficiency of 0.77, higher than conventional metals.     

Development and Validation of a Novel Bird Strike Resistant Composite Leading Edge Structure

A novel design of a fibre-reinforced composite Leading Edge (LE) of a Horizontal Tail Plain (HTP) is proposed. The development and validation approach of the innovative composite LE structure are described. The main design goal is the satisfactory impact resistance of the novel composite LE in the case of bird strike. The design concept is based on the absorption of the major portion of the bird kinetic energy by the composite skins, in order to protect the ribs and the inner LE structure from damaging, thus preserving the tail plane functionality for safe landing. To this purpose, the LE skin is fabricated from specially designed composite panels, so called ‘tensor skin’ panels, comprising folded layers, which unfold under the impact load and increase the energy absorption capability of the LE. A numerical model simulating the bird strike process is developed and bird strike experimental testing is performed, in order to validate the proposed layout and prove the capability of the structure to successfully withstand the impact loading. The numerical modelling issues and the critical parameters of the simulation are discussed. The present work is part of the European Aeronautics Research Project, ‘Crashworthiness of aircraft for high velocity impact – CRAHVI’ [1].     

Manufacture of Composite Panels with J-Shape Stiffeners

The use of composite materials in primary structure of aircraft is becoming more common. Stiffened composite panels have been designed for a variety of load carrying conditions in aircraft. In this, study, manufacturing techniques for stiffened composite panels were reviewed and discussed. Co-curing and secondary bonding manufacturing techniques were used to produce four stiffened composite panels. Experience gained with these techniques is discussed. Ultrasonic C-scan inspection was carried out to detect any defects in the panels. These panels were tested in compression to verify their structural capability in the post-buckled state. This paper presents the details of the tool design concepts and manufacturing techniques, and identifies and discusses the advantages and disadvantages of each manufacturing technique.     

Axial crush and bending collapse of an aluminum/GFRP hybrid square tube and its energy absorption capability

In this paper, energy absorption capability of axial crush and bending collapse of aluminum/GFRP hybrid tubes were investigated. Glass fiber–epoxy composite prepregs were wrapped around an aluminum tube and then cured completely in the autoclave under the recommended cure cycle. Bonding process between composite and aluminum tubes was performed by excess resin extracted from the composite tube during curing process. For comparing energy absorption characteristics of the hybrid tube with those of pure aluminum and composite tubes, tests were performed using specimens made of an aluminum alloy and a composite material, respectively.

Failure mechanisms of the hybrid tube under the axial compressive load and the bending load were experimentally investigated. For calculating energy absorption capability of axial crush and bending collapse behaviors of the hybrid tube, the modified plastic hinge collapse model and the modified Kecman's model for hybrid tube were suggested, respectively. Two suggested models for the hybrid tube showed a good agreement with the experimental results.     

复合材料帽形加筋壁板轴压屈曲与后屈曲性能

针对2种边界条件和3种板元宽度情况,采用几种屈曲方法对轴压载荷作用下的复合材料帽形加筋壁板进行了计算,得到了不同情况下的屈曲载荷,通过对复合材料加筋壁板几种计算方法的计算结果与试验结果的对比,得到一种更简单有效计算复合材料帽形加筋壁板轴压屈曲载荷的方法;依据帽形加筋壁板的结构特点和试验后的破坏模式,提出一种估算复合材料帽形加筋壁板轴压破坏载荷的方法,用该方法在几个项目上的计算结果与试验结果进行比较,发现两者较吻合,验证了复合材料帽形加筋壁板轴压承载能力估算方法的合理性,为结构设计人员在初始设计阶段对复合材料帽形加筋壁板轴压强度评估提供了一种简洁的途径。