复合材料加筋板铺层优化设计的等效弯曲刚度法

借助于等效弯曲刚度法和遗传算法,建立了一种复合材料加筋板铺层顺序优化设计算法.等效弯曲刚度法基于层合板的弯曲刚度与其失稳载荷一一对应的关系,将任意铺层顺序的层合板等效成一个只有8层的对称铺层的辅助层合板,通过优化辅助层合板,得到层合板的最优弯曲刚度参数,最后以获得的最优弯曲刚度参数为约束应用遗传算法进行铺层顺序优化,获...     

开孔复合材料层合板强度不确定性分析

以拉伸载荷作用下AS4/3501-6开孔复合材料层合板为研究对象,采用考虑复合材料层合板就地强度效应的有限断裂力学模型和基于方差的敏感性测度分析模型相结合的方法,研究单层板宏观力学性能不确定性对具有不同孔径和铺层顺序的开孔复合材料层合板破坏强度的影响．研究结果表明：单层板力学性能对开孔板强度影响程度的大小与孔径相关,但敏感性排序与孔径无关．同时,单层板力学性能敏感性测度与层合板铺层顺序有关,层合板各向异性比越大,开孔板拉伸破坏受单层板纤维方向拉伸强度的影响越大,而且开孔板拉伸强度与单层板纤维方向拉伸强度呈正相关,与横向弹性模量呈负相关,与面内剪切模量和纵向弹性模量不具有单调关系．     

非对称铺层复合材料层合板质量优化设计

复合材料广泛应用于航空航天等领域,追求轻量化设计已经成为研究重点.对复合材料层合板质量优化设计,可以减少层合板的纤维用量,减小层合板的质量,降低成本.首先研究复合材料层合板在承受轴向载荷时,产生的形变量、应力示意图,分析容易发生失效部位;以层合板铺层厚度为设计变量,最大应变、铺层比例等为约束条件,最小化层合板质量为优化...     

错位铺层拼接层合板承载机制的试验与模拟研究

针对具有特殊细观结构的非均匀连续复合材料--错位铺层拼接层合板,测定了其拉伸强度和刚度,并观测了其断口破坏特征和表面铺层的应变分布;基于细观结构,建立了包含基体损伤演化的三维有限元模型,并进行数值模拟分析,研究了材料的传力和破坏机理。结果表明：铺层间断使断点附近及相邻层受间断影响处形成了局部高应变梯度,断裂模式为基体剪切破坏;铺层间断点处的载荷通过基体承剪的方式传递,远离间断点处则仍靠纤维传载;随着断点间距(在3mm~9mm范围内变化)的增大,强度和刚度逐渐增加,但幅度不超过1.4%和3.3%。     

不同铺层角含孔复合材料板的损伤研究

针对0o、45o、90o铺层角复合材料层合板的含孔结构损伤问题,提出了一种基于层合板各铺层孔边应力解析解的首次损伤载荷系数分析计算模型。根据非均匀各向异性层合板的弹性特性,采用复变函数曲线映射方法获取了层合板孔边界积分方程,计算获得了0o、45o、90o角度铺层层合板各铺层的孔边纤维主方向和垂直于纤维主方向的应力分量;采用Tsai-Hill强度理论,对层合板各铺层进行孔边首次损伤载荷系数计算。分析结果表明:试件左右两端面在受到均布拉伸载荷p的作用下,各铺层中具有90o铺层角的铺层首次损伤载荷系数最小,具有0o铺层角的铺层首次损伤载荷系数最大,说明具有90o铺层角的铺层最先出现损伤,对应铺层首次损伤出现在孔边90o方向区域。将计算值与现有文献结果进行比较,误差小于10%,二者具有较好的一致性。     

错位铺层拼接层合板力学性能分析与模拟方法探索

针对特殊使用条件,需使用单向带逐层拼接或对接方法制备复合材料层合板,层合板内存在大量的,有意设计的间断点.论文首先通过多种方法测定试件不同位置应变数据来计算不同参数下刚度值变化情况,然后基于可反映错位铺层拼接层合板结构的细观尺度,使用ABAQUS有限元,将层合板中存在间断的增强纤维视为rebar-layer插入树脂基体,建立表征结构、纤维体积百分含量相符的等效模型进行模拟.经对比模拟与试验结果可见,该方法模拟结果准确,贴近真实情况;有效反映出参数不同所引起试样刚度变化特征.     

含椭圆孔的变角度复合材料层合板的屈曲性能研究

本文利用变角度复合材料的纤维方向角可沿平面位置任意连续变化的特点,提出在孔附近采用与孔同心的椭圆曲线作为纤维铺设路径的层合板铺层方案,以改善含椭圆孔的层合板的孔边应力集中,进而提高层合板的抗屈曲性能．主要研究内容有：利用ABAQUS软件分析本文提出的孔边特殊铺层方式下变角度复合材料层合板的面内应力分布及屈曲性能,通过与传统直线铺层方式以及线性变角度铺层方式进行比较,说明了本文提出的新铺层方式的优越性,并详细分析了椭圆孔的离心率、开孔尺寸及开孔方位对层合板的屈曲临界荷载的影响．研究结果可为含椭圆孔的变角度复合材料层合板的结构设计和优化提供一定的参考．     

复合材料铺层拼接层间断裂韧性的试验研究

针对评价复合材料层合板层间断裂韧性的测量,提出了用拉伸试验法测定Ⅱ型层间断裂韧性,设计了内含铺层拼接区的分层破坏试验层合板,制备了拉伸试件.通过拉伸试验测得了拼接区开裂和分层裂纹稳态扩展过程中的载荷与变形规律:层间破坏具有Ⅱ型断裂特征,且裂纹扩展比较稳定.利用测试数据计算出断裂功,并以临界能量释放率表示层合板的Ⅱ型层间断裂韧性,结果表明用铺层拼接件拉伸法进行层间断裂韧性试验是可行的.     

飞机复合材料气密舱门布局和铺层的两级优化设计

针对飞机复合材料气密舱门的轻量化设计,提出了一种两级优化方法。第一级优化方法以结构应变能最小为目标,对横向加强筋的相对位置进行布局优化;在第一级优化结果的基础上,第二级优化方法借助于等效弯曲刚度法和遗传算法,以舱门强度、刚度和复合材料失效准则为约束条件,进行内外蒙皮、环框和横向加强筋的铺层优化;通过两级之间的迭代,最终得到结构布局和铺层的最优方案。对某个型号飞机舱门的优化结果表明:布局优化后舱门最大位移和最大应力分别降低了22.7%和11.2%,舱门刚度和强度得到了明显的改善;铺层优化后舱门质量降低了7.69%。本文研究为复合材料气密舱门实现结构减重提供了一种有效的方法。     

含铺层拼接层合板的剪切强度

对含铺层拼接的碳纤维增强树脂基复合材料层合板进行了剪切强度实验研究.从三种不同铺层拼接角层合板上切取含缺口的剪切试件,通过实验测定了其载荷-位移曲线,得到了剪切强度值.实验结果表明,三组试件的剪切强度基本相同,即拼接层角度改变几乎不会引起层合板的剪切强度发生明显变化.采用有限元软件ABAQUS6.5对实验过程进行模拟,得到拼接层角度改变将引起拼接层中0°层出现切应力集中,但沿缺口切应力的平均值几乎不变.这也说明拼接层角度的变化几乎不影响层合板的剪切强度.     

Kevlar/环氧树脂层合材料的动静态力学性能及本构关系

利用MTS和SHPB装置开展了Kevlar / 环氧树脂层合材料动静态力学性能实验研究,详细讨论了应变率和纤维铺设方式的不同所引起的材料力学行为的差异。根据实验结果提出了一种经验型本构模型,该模型不仅考虑了材料的应变率硬化、损伤软化效应,还通过增强系数的引入描述了纤维铺设方式对材料力学性能的影响。     

An experimental study of dynamic delamination of thick fiber reinforced polymeric matrix composites

Dynamic delamination of thick fiber reinforced polymeric matrix composite laminates is investigated using optical techniques and high-speed photography. The laminates used in this work are graphite/epoxy fiber reinforced, 65 percent fiber volume fraction, composite plates consisting of 48 plies (6 mm plate thickness). Two different laminate layups are tested: a quasi-isotropic arrangement and a unidirectional arrangement. The experimental setup consists of 152 mm×152 mm square plates impact loaded in an outof-plane configuration using a high-speed gas gun. Impact speeds range from 1 m/s to 30 m/s. Real-time imaging of the laminate out-of-pane displacement is performed using the lateral shearing interferometer of coherent gradient sensing (CGS) in conjunction with high-speed photography. Onset of dynamic delamination can be observed, and quantities such as delamination speeds (in some cases up to 1800 m/s) are measured and reported. A brief comparison is made with dynamic fracture experiments of the same material conducted in a separate study.     

混杂短纤维增强复合材料弹性模量预测

在现代工程结构中,纤维增强复合材料具有较高的刚度重量比、优异的耐久性和设计灵活性等优点,因此得到了广泛应用．本文结合细观力学中的Mori-Tanaka方法和Halpin-Tsai方法推导了混杂碳纤维和玻璃纤维增强复合材料有效弹性模量的解析表达式．通过引入参数λ,提出了计算随机方向混合纤维增强复合材料弹性模量的新模型,分析了纤维长径比和体积分数对复合材料弹性模量的影响．结果表明,复合材料的弹性性能对纤维长径比和体积分数非常敏感．根据提出的理论,混杂纤维增强复合材料的弹性模量处于单一纤维（纯碳纤维或纯玻璃纤维）增强复合材料弹性模量之间．对于单一纤维增强复合材料,采用Halpin-Tsai方法计算的复合材料弹性模量高于Mori-Tanaka方法计算结果．     

Concurrent multi-scale design optimization of composite frame structures using the Heaviside penalization of discrete material model

This paper deals with the concurrent multi-scale optimization design of frame structure composed of glass or carbon fiber reinforced polymer laminates. In the composite frame structure, the fiber winding angle at the micro-material scale and the geometrical parameter of components of the frame in the macro-structural scale are introduced as the inde-pendent variables on the two geometrical scales. Considering manufacturing requirements, discrete fiber winding angles are specified for the micro design variable. The improved Heaviside penalization discrete material optimization inter-polation scheme has been applied to achieve the discrete optimization design of the fiber winding angle. An optimiza-tion model based on the minimum structural compliance and the specified fiber material volume constraint has been estab-lished. The sensitivity information about the two geometrical scales design variables are also deduced considering the char-acteristics of discrete fiber winding angles. The optimization results of the fiber winding angle or the macro structural topology on the two single geometrical scales, together with the concurrent two-scale optimization, is separately studied and compared in the paper. Numerical examples in the paper show that the concurrent multi-scale optimization can fur-ther explore the coupling effect between the macro-structure and micro-material of the composite to achieve an ultra-light design of the composite frame structure. The novel two geometrical scales optimization model provides a new oppor-tunity for the design of composite structure in aerospace and other industries.     

纤维增强复合材料热隐身斗篷设计

基于变换热动力学原理可获得具有热隐身性能的隐身结构(隐身斗篷)所需要的材料性质的空间分布。但这种材料性质的复杂分布形式以及局部热传导性能无限大等极值性质需求,使得隐身斗篷设计的实现非常困难,需要研究基于常规材料的隐身斗篷设计。本文基于常规材料的热隐身结构实现问题,提出了基于纤维增强复合材料圆环结构的实现热隐身的结构形式。首先,基于变换热动力学原理获得热隐身所需的热传导系数沿半径方向的变化规律;进而,通过设计复合材料不同位置的纤维铺设方式(含量和铺设方向)实现热隐身对材料性能的需求。选择金属银作为纤维,空气作为基体,设计出了具有热隐身性能的复合材料圆环结构纤维含量和铺设方向沿径向的分布方案。对该设计方案进行数值仿真,结果显示所设计的隐身结构具有良好的热隐身性能。由于设计方案基于常规材料,因此具有容易实现的优点。     

Buckling and post-buckling analyses for an axially compressed laminated cylindrical shell of FGM with PFRC in thermal environments

In this paper, investigation on buckling and post-buckling behaviors of a laminated cylindrical shell of functionally graded material (FGM) with the piezoelectric fiber reinforced composite (PFRC) actuators subjected to thermal and axial compressed loads is presented. Based on the Donnell assumptions, the material properties of the FGM layer vary smoothly through the laminated cylindrical shell thickness according to a power law distribution of the volume fraction of constituent materials. In the present study, a numerical procedure for the laminated cylindrical shell is used based on the Ritz energy method and the nonlinear strain–displacement relations. Some useful discussion and numerical examples are presented to show various effects of temperature field, volume fraction and geometric parameters on the buckling and post-buckling behaviors of the laminated cylindrical shell with PFRC.     

Nonlinear low-velocity impact on damped and matrix-cracked hybrid laminated beams containing carbon nanotube reinforced composite layers

This paper investigates the low-velocity impact response of a shear deformable laminated beam which contains both carbon nanotube reinforced composite (CNTRC) layers and carbon fiber reinforced composite (CFRC) layers. The effect of matrix cracks is considered, and a refined self-consistent model is selected to describe the degraded stiffness caused by the damage. The beam including damping effects rests on a two-parameter elastic foundation in thermal environments. Based on a higher-order shear deformation theory and von Kármán nonlinear strain–displacement relationships, the motion equations of the beam and impactor are established and solved by means of a two-step perturbation approach. The material properties of both CFRC layers and CNTRC layers are assumed to be temperature-dependent. To assess engineering application of this hybrid structure, two conditions for outer CNTRC layers and outer CFRC layers are compared. Besides, the effects of the crack density, volume fraction of carbon nanotube, temperature variation, the foundation stiffness and damping on the nonlinear low-velocity impact behavior of hybrid laminated beams are also discussed in detail.

     

Numerical prediction of the thermal conductivity of fibers

The need to determine the thermal conductivity of fibers for design purposes of new composite materials and the inherent difficulties in the direct measurement of the thermal conductivity of fibers motivated the present work due to its importance for energy conservation purposes. In this work, a correlation formula is developed to predict the thermal conductivities of fiber as function of the effective thermal conductivity of a fiber-reinforced composite laminates and their constituents which are easy to measure. The parallel and series thermal models of composite walls have been utilized in developing this correlation equation. The coefficients of this formula can be given as functions of the voids volume fraction for each fiber to resin volume ratio considered. The validity of the models is verified through finite element analysis. This model also shows excellent agreement with the available experimental values.     

低速冲击下纤维/金属层合板抗分层性能研究

本文采用内聚力模型,对纤维/金属层合板(FMLs)在低速冲击载荷作用下抗分层性能进行研究。内聚力模型对裂纹的模拟具有它独特的优势：一是该模型不需要预先假设初始缺陷;二是在计算过程中随着裂纹的扩展,该方法不需要重新对结构进行网格划分。借助该模型,本文对低速冲击载荷作用下,纤维层合板(FRP)分层进行了模拟,并验证了该模型计算的有效性。在此基础上,本文研究了低速冲击载荷作用下,不同金属含量的纤维/金属层合板抗分层性能,并与纤维层合板进行了比较。最后从能量的角度讨论了金属含量与铺层结构对FMLs低速冲击性能的影响。     

杆弹侵彻钢纤维混凝土实验研究

采用DOP实验方法,进行了35CrMnSiA杆弹对不同钢纤维体积含量的钢纤维混凝土的侵彻实验.分别研究了杆弹着速和钢纤维体积含量对钢纤维混凝土杭侵彻性能的影响.实验表明,随着弹速增加,不同钢纤维含量的钢纤维混凝土侵彻深度都会增加,但钢纤维混凝土中弹体便深增加较素混凝土缓慢;而钢纤维能增强混凝土的抗侵彻性能,且随钢纤维体...