基于几何因子的复合材料气动弹性剪裁设计

实现了基于几何因子的复合材料层合板建模,解决了几何因子与Natran的参数输入问题,并根据工艺约束中的最小铺层比例对几何因子可行空间进行了推导补充。在此基础上,提出了一种基于几何因子和Nastran的复合材料气动弹性剪裁优化设计方法。首先以总厚度和几何因子作为设计变量以及以Nastran作为求解器,以强度、刚度、颤振和发散速度以及几何因子相关性约束作为约束条件进行结构寻优,得到最优的铺层总厚度和几何因子。其次,以最优几何因子作为目标,进行铺层结构逆问题求解,约束条件为复合材料铺层工艺约束。因几何因子为铺层厚度和铺层顺序的表达式,与传统的多级优化相比,以几何因子作为设计变量可以避免铺层厚度和铺层顺序的解耦,进而获得更大的设计空间,且得到的铺层结构可以满足工艺约束。最后,对一矩形悬臂复合材料层合板进行剪裁设计,使得铺层结构满足气动弹性约束且质量最小。结果显示,运用该优化方法可以得到质量更小且满足工艺约束的铺层结构。     

基于复合材料层合箱梁改进解析模型计算等效刚度

提出了基于复合材料层合箱梁改进解析模型的等效刚度计算方法。在考虑三维应变效应的同时用复合材料单层的二维折算模量分量来表示三维折算模量分量,简化了复合材料层合箱梁等效刚度系数的计算,得到了由梁横截面几何尺寸和层合板刚度系数表达的等效抗弯刚度和等效抗扭刚度的解析式。该解析式适用于环向刚度一致的复合材料层合箱梁,并充分考虑了弯曲-剪切耦合和扭转-拉伸耦合效应对等效刚度的影响。通过三点弯试验和扭转试验,验证了解析式的正确性;通过与分层等效叠加法、有限元法进行对比,分析了解析式的计算精度。结合经典层合板理论,研究了铺层方式对等效刚度产生的影响及原因,预测了不同铺层复合材料层合箱梁等效刚度的变化规律。      

传递矩阵法分析复合材料层合板的传声损失

为了得到不同频率下正交各向异性复合材料层合板的传声损失,基于传递矩阵的方法,推导出层合板的传声损失计算公式。通过建立复合材料层合板的传声计算模型,研究了层合板铺设角度、板厚度和板密度等结构参数对层合板的传声损失影响。计算结果表明：复合材料的密度与传声损失之间没有明显的线性关系,而是随着频率的增加而上升;层合板的总厚度越大,传声损失也越大,而且各层之间厚度不同,也会引起传声损失的较大改变;层合板铺层角度越大,传声损失也越大。采用传递矩阵法能充分考虑复合材料层合板的铺设方式和铺层角度等因素的影响,利用层合板层间的速度和应力连续边界条件,准确的反应复合材料层合板隔声性能。     

基于非对称复合材料层合板的准零刚度隔振系统

提出了基于正交铺设复合材料层合板的准零刚度隔振系统。采用理论分析与有限元方法研究了有残余热应力的正交铺设复合材料层合板的双稳定特性及负刚度特性。发现层合板具有负刚度特性的变形区间随层板厚度增加而逐渐变窄。正交铺设复合材料层合板在其厚度略厚于失去双稳定特性临界厚度时具有准零刚度特性。利用准零刚度正交铺设复合材料层合板构造了简单的隔振系统,研究其在中心加速度激励下的加速度传递幅值,并与线性隔振系统的隔振效果进行比较。结果显示该准零刚度隔振系统固有频率低于线性隔振系统固有频率,加速度传递峰值小于线性隔振系统,有效隔振频率范围宽于线性隔振系统。     

圆锥头弹体冲击复合材料层合板数值模拟

采用ABAQUS软件建立了圆锥头弹体正冲击复合材料层合板的有限元模型,并与已有文献结果进行对比验证了模型的可靠性,进而研究圆锥头弹体以不同的入射角度冲击复合材料层合板时初始速度与剩余速度的关系、复合材料层合板的破坏形态及弹体发生跳弹的规律。结果表明：弹体以90°入射角冲击复合材料层合板,在距离临界速度较大时,弹体的剩余速度与初始速度呈线性关系;不同的初始速度对复合材料层合板的损伤面积和破坏机制也不相同;弹体的入射角度越小、复合材料层合板越厚,越容易产生跳弹现象,并给出了入射角度和铺陈层数对跳弹现象的影响规律。该研究可为各种防护装备的设计和优化提供参考。     

复合材料壁板铺层参数对大展弦比机翼气动弹性优化的影响

开展了大展弦比复合材料机翼气动弹性综合优化设计研究,以复合材料层合板铺层厚度为设计变量,以多种气动弹性约束与强度/应变约束为限制条件对结构进行优化设计,从铺层比例和铺层非均衡两方面分析了蒙皮铺层参数的影响。研究表明: 在满足综合约束的条件下,随着0°铺层比例的增加,翼尖变形略微减小,颤振速度略有下降,副翼效率变化不大; 蒙皮铺层非均衡程度主要影响机翼静气动弹性能,随着蒙皮非均衡引起的机翼刚轴绕翼根向前缘逐渐偏转,翼尖垂直变形变化不明显,但翼尖负扭转变形的绝对值加大,副翼效率下降。     

含面内波纹缺陷的复合材料层合板刚度性能

基于经典层合板理论（CLT）,并考虑面内波纹引起的拉伸-弯曲耦合作用,提出了含面内波纹缺陷的复合材料层合板刚度预测模型,定量研究了波纹比、纤维偏转角和波纹位置等面内波纹参数对其三维刚度性能的影响。结果表明：理论模型预测值与文献中的结果吻合较好;面内波纹对纵向弹性模量、横向弹性模量、面内剪切模量、主泊松比和面内弯曲刚度均产生了显著影响。该建模方法为研究波纹缺陷对复合材料力学性能影响提供了参考。     

多分层对复合材料层合板自振特性的影响

基于Mindlin一阶剪切理论分项等参插值的有限元法, 建立了含多个分层损伤复合材料层合板自由振动分析的有限元模型和分析方法, 并采用线性接触模型模拟分层区域上、 下子板的相互作用。通过典型数值算例, 讨论了分层位置、 数目及板的边界条件诸参数对其振动特性的影响。结果表明: 分层位置沿板长方向变化时, 中间分层的频率变化范围较大, 表面分层变化较小, 但变化趋势基本相同; 沿层合板厚度方向, 多分层中最长分层的位置越靠近层合板中面, 则其对振动特性的影响越大; 多个分层位置较靠近层合板表面, 且板边界条件约束较弱时, 多分层与单分层对振动特性影响的差别不大, 此时, 可将多分层损伤层合板简化为单分层损伤层合板来进行振动分析。      

基于二维等效FE-SEA混合方法的复合材料层合板传声损失分析

为研究湍流脉动噪声激励下复合材料层合板的传声特性,首先基于一般层合板理论将复合材料层合板等效为单层各向异性板,进而采用FE-SEA混合方法研究其传声损失。同时开展复合材料层合板传声损失试验,并将FE-SEA结果和统计能量法(SEA)结果以及实验值进行对比分析。研究结果表明:FE-SEA结果和实验值整体上分布趋势一致,而且误差也相对较小,其中3 000 Hz～10 000 Hz误差在2 dB以内,但由于刚度等效导致2 000 Hz附近结果误差相对较大。相较于SEA方法, FE-SEA混合方法综合考虑了复合材料层合板边界条件和详细得几何特征,不仅可以准确地计算复合材料层合板的固有特性,而且使得传声损失结果在全频带内与试验值吻合得更好。因此建立的二维等效FE-SEA混合模型可以准确预示复合材料层合板在湍流脉动噪声激励下的传声损失。     

复合材料层合板多尺度交互渐进损伤分析

纤维增强复合材料强度的准确表征是复合材料力学性能研究的核心问题之一。该文以碳纤维增强树脂基复合材料层合板为研究对象,基于宏观-细观多尺度分析方法,根据复合材料的物理失效模式分别给出了基体和纤维的细观失效准则,同时考虑基体失效对复合材料层合板纤维轴向力学性能的影响。提出了新的刚度退化方式,可准确表征复合材料层合板的损伤演化过程,开展了复合材料层合板四点弯模型的多尺度交互渐进损伤分析和试验验证。结果表明:基于多尺度方法的复合材料层合板宏-细观交互渐进损伤分析结果与试验结果吻合较好,新的刚度退化方式可以准确模拟层合板的失效过程。     

Effect of stacking sequence on the torsional stiffness of the composite drive shaft

Torsional stiffness is an important parameter judging the performance of composite drive shaft. In this paper, a new mechanical analytical solution of torsional stiffness for the composite drive shaft with balance laminate is derived based on classical lamination theory and mechanical analysis. Finite element analysis (FEA) has been used to calculate the torsional stiffness of carbon fiber-reinforced plastic (CFRP) drive shaft. A torsion test platform has also been constructed to measure the torsional stiffness of CFRP drive shaft specimens. Results of the mechanical analytical solution, FEA, and experiments show that the composite tube with the location of ±45° layers near to the outer surface is larger than the ones with the location of ±45° layers near to the inner surface. The effect of stacking sequence on torsional stiffness is larger in the thick-walled than that in the thin-walled composite drive shaft. The mechanical analytical solution can complement classical lamination theory which cannot reflect the effect of stacking sequence in calculating the torsional stiffness.     

Damping optimization of symmetrically laminated plates with transverse shear deformation using lamination parameters

This paper deals with the damping characteristics of symmetrically laminated plates with transverse shear deformation. First, the effect of laminate configuration on the damping characteristics is investigated for cantilevered laminated plates based on the Reissner–Mindlin’s first-order shear deformation theory. To examine the effect of laminate configuration, the concept of specific damping capacity is introduced and the damping characteristics are represented on the lamination parameter plane, where the damped stiffness invariants in transverse shear are newly proposed in this paper. Next, the optimal laminate configurations for the cantilevered laminated plates with maximal damping are determined taking into account the transverse shear effect by using differential evolution in which lamination parameters are used as intermediate design variables. The relation between the laminate configurations and the damping characteristics is discussed based on the concept of lamination parameters.     

Structural optimization of an aeroelastically tailored composite flat plate made of woven fiberglass/epoxy

Summary Effects of aspect ratio, sweep angle, and stacking sequence of laminated composites were studied to find the optimized configuration of an aeroelastically tailored composite wing idealized as a flat plate in terms of flutter speed. The aeroelastic analysis has been carried out in the frequency domain. The modal approach in conjunction with doublet-lattice method (DLM) has been chosen for structural and unsteady aerodynamic analysis, respectively. The interpolation between aerodynamic boxes and structural nodes has been done using surface splines. To study the effect of stacking sequence the classical lamination theory (CLT) has been chosen. The parametric studies showed the effective ply orientation angle to be somewhere between 15 and 30 degrees, while the plates with lower aspect ratio seem to have higher flutter speeds. Forward-swept configurations show higher flutter speed, yet imposed by divergence constraints.     

A simulated annealing method for design of laminates with required stiffness properties

Designing a laminate based on its stiffness properties requires finding the optimum lamination stacking sequence to yield the required stiffness properties. The design variables to be considered are the number of layers and orientation angle of fibers in each layer group, which are treated as discrete-variables. The optimum lamination is then obtained by minimizing a cost function composed of the relative difference between the calculated effective stiffness properties and weight of trial laminate and the desired properties. This error minimization problem was solved using a modified simulated annealing heuristic method. The new simulated annealing implementation comprises a cooling procedure in which the temperature decrease relied adaptively on the objective function evolution. It is shown that the proposed method can give rise to an improvement in convergence speed. To achieve a further improvement in the performance of the method, simulated annealing parallelization implemented using the proposed cooling process. The main features of this algorithm are described and its encouraging results are presented.     

双层桥面桁架梁软颤振特性风洞试验研究

随着城市交通量的日益增大,双层桥面桁架梁的应用需求日益增加,研究其颤振特性有助于提升该类加劲梁的抗风设计水平。以武汉杨泗港长江大桥双层桥面桁架主梁为对象,利用节段模型自由振动风洞试验,测试了该主梁模型在不同工况下的软颤振特性,对比了不同风速条件下软颤振形态的异同。研究表明,双层桁架梁在试验中表现出了明显的软颤振特性,其振幅也随风速增加而增大。在0°风攻角的各级试验风速下,软颤振形态均表现为偏心扭转运动;在3°和5°风攻角下,起初表现为弯扭耦合运动,随着风速增大,弯扭耦合运动相位差逐渐减小;当风速增大到某个值后,弯扭耦合相位差为零,耦合颤振转变为偏心扭转颤振。无论是在连续的升风到降风过程中,还是在固定风速下给予不同初始激励,模型的软颤振振幅与折算风速之间具有唯一对应关系,不存在同一折算风速对应不同振幅的情况以及不同折算风速对应相同振幅的情况。最后从气动阻尼同时随振幅和折减风速变化的角度初步解释了双层桁架梁软颤振的发生机理。     

桥梁断面颤振导数的CFD全带宽识别法

由于需要在不同折算风速下重复进行大量试验或CFD(Computational Fluid Dynamics)模拟,现有风洞试验和CFD方法识别桥梁断面颤振导数耗时且效率低。提出一种基于CFD离散时间气动模型,快速识别感兴趣折算风速带宽内任意折算风速下桥梁断面颤振导数的全带宽识别法。该法基于任意拉格朗-欧拉描述的有限体积法和多层网格技术,首先计算作用在桥梁断面上的非定常气动力,CFD模拟时强迫桥梁断面以单自由度竖弯或扭转方式振动,位移模式为定义在感兴趣的频率范围内的指数脉冲时间序列。然后利用得到的气动力和该指数脉冲输入,通过系统识别建立起反映桥梁断面气动力系统特性的离散时间气动模型。随后利用该气动模型仿真桥梁断面在简谐位移激励下的气动力响应,并由该模型的输入和响应通过系统识别得到桥梁断面的颤振导数。该法在竖弯和扭转方向各仅需一次CFD模拟,就可构造离散时间气动模型,使得颤振导数识别的计算量显著降低。开展了三汊矶大桥加劲梁断面颤振导数识别和颤振临界风速计算,研究结果与风洞试验的一致性,证明了方法的可靠性和高效性。     

Dynamic stability behavior of damped laminated beam subjected to uniformly distributed subtangential forces

The dynamic stability behavior of damped laminated beam with various boundary conditions subjected to the uniformly distributed subtangential forces is investigated using the finite element formulation. The formal engineering approach of the mechanics for the thin-walled laminated beam based on kinematic assumptions consistent with Vlasov beam theory is used. An extended Hamilton’s principle is employed to obtain the mass-, damping-, elastic stiffness-, geometric stiffness matrices, and the load correction stiffness matrix due to the subtangential forces, respectively. The method for the evaluation of critical values for divergence and flutter of the nonconservative systems is briefly introduced in case of considering and neglecting damping effects. Throughout numerical examples, the influence of various parameters on the dynamic stability behavior of the nonconservative laminated beam is newly investigated: (1) the variation of the divergence and flutter loads due to the nonconservativeness with respect to the fiber orientation, (2) the effect of boundary condition on the instability region of the divergence-flutter system, and (3) the influence of external and internal damping on the flutter load.     

加筋板总体失稳分析的等效层合板模型

基于等效刚度的思想,通过设定层合板的属性参数模拟了加筋板结构的力学特性,提出了一种适用于不同截面形状以及布局形式的加筋板总体失稳分析的等效层合板建模方法。利用PATRAN/NASTRAN 软件比较了反映实际壁板形状的高精度有限元模型与对应的赋有层合板属性的等效刚度简化模型。对于工程中常见形状的加强筋以及不同布局形式的壁板,2种模型的一阶线性失稳因子基本一致,从而验证了将等效层合板模型用于加筋壁板结构的稳定性分析可以满足工程精度要求,并显著提高了计算效率。