旋转SMA纤维混杂复合材料薄壁梁的自由振动

研究具有SMA主动纤维的旋转复合材料单闭室薄壁截面梁的耦合自由振动问题.基于Hamilton原理并结合SMA纤维复合材料薄壁梁的二维截面内力(矩)与位移(转角)关系方程,导出旋转单闭室截面薄壁复合材料梁的1D耦合自由振动分析模型.该模型还考虑薄壁梁调矩角和预锥角的作用.采用Galerkin法求解振动模型,获得梁耦合振动...     

复合材料单闭室薄壁梁弯曲与扭转分析

本文主要讨论复合材料单闭室薄壁梁的弯曲与扭转，重点研究横向剪切和限制翘曲的影响。在复合材料薄壁梁弯曲与扭转经典分析理论的基础上，建立了一种能够考虑横向剪切和限制翘曲影响的复合材料单闭室薄壁梁弯曲与扭转分析方法。     

轴向受载的Timoshenko薄壁梁的弯扭耦合动力响应

利用简正模态法研究各种集中载荷和分布载荷作用下单对称轴向受载的Timoshenko薄壁梁的弯扭耦合动力响应。该弯扭耦合梁所受到的载荷可以是集中载荷或沿着梁长度分布的分布载荷。目前研究中采用考虑了轴向载荷、剪切变形和转动惯量影响的Timoshenko薄壁梁理论。首先建立轴向受载的Timoshenko薄壁梁结构的普遍运动微分方程并进行其自由振动的分析。一旦得到轴向受载的Timoshenko薄壁梁的固有频率和模态形状，利用简正模态法计算薄壁梁结构的弯扭耦合动力响应。针对具体算例，提出并讨论了动力弯曲位移和扭转位移的数值结果。     

确定性载荷作用下Timoshenko薄壁梁的弯扭耦合动力响应

建立了一种普遍的解析理论用于求解确定性载荷作用下Timoshenko薄壁梁的弯扭耦合动力响应。首先通过直接求解单对称均匀Timoshenko薄壁梁单元弯扭耦合振动的运动偏微分方程，给出了计算其自由振动的精确方法，并导出了Timoshenko弯扭耦合薄壁梁自由振动主模态的正交条件。然后利用简正模态法研究了确定性载荷作用下单对称Timoshenko薄壁梁的弯扭耦合动力响应，该弯扭耦合梁所受到的荷载可以是集中载荷或沿着梁长度分布的分布载荷。最后假定确定性载荷是谐波变化的，得到了各种激励下封闭形式的解，并对动力弯曲位移和扭转位移的数值结果进行了讨论。     

复杂工程约束下基于NSGA-Ⅲ的车身梁截面优化设计

在汽车概念设计阶段,车身常由薄壁梁简化而成,其截面对轿车白车身刚度有直接影响。多室的薄壁梁截面极其复杂,在设计过程中不仅需考虑其力学性能,还需符合制造加工过程的各种工艺约束。本文基于薄壁梁截面设计的装配性与制造性等实际工程约束,提出一种梁截面形状控制方法以兼容多种工程约束。定义了梁截面多目标优化模型,以基于参考点的遗传算法NSGA-Ⅲ作为高维多目标优化问题算法,实现了相应的软件模块对截面惯性矩和扭转常量等参数进行优化。最终通过算例测试证明此方法的有效性。     

具任意脱层复合材料梁的非线性谐波响应

研究了具任意脱层复合材料梁的非线性谐波响应问题。基于弹性理论，建立了考虑剪切变形时的复合材料梁脱层的基本方程式。在空间上采用B样条函数和Galerkin积分法，在时间上采用增量谐波平衡法进行计算。通过实例计算，得出了简谐力作用下的非线性动力响应曲线。认为基谐波振动仍是非线性振动的主要部分。     

Further discussion on the effect of shear deformation on structure displacement in structural mechanics

剪切变形对位移的影响程度，不仅取决于高跨比，截面形式对其影响也较大. 通过实例讨论了工程中广泛采用的三种形式截面：一般截面、薄壁型截面、复合材料截面. 分析表明：（1） 相较于一般截面形式，薄壁型截面梁中剪切变形对位移的影响较大，尤其是短而高的薄壁梁，剪切变形引起的位移更不能忽略. （2） 复合材料截面梁，剪切变形引起的位移受截面材料弹性模量比、不同材料截面高度比影响较大：截面材料弹性模量比越大，加强材料越厚，剪切变形对位移的影响越大. 这会导致复合材料截面，即使是细长的梁，剪切变形引起的位移有时也不能忽略.     

考虑约束扭转的薄壁梁单元刚度矩阵

推导了薄壁空间梁单元刚度矩阵 ,考虑了双向弯曲及截面约束扭转对杆件轴向变形的影响 ;计算了截面的翘曲变形 ,以及二次剪应力对翘曲变形的影响 ,可适用于任意截面 (包括开口、闭口和混合剖面 )的薄壁杆件。计算结果表明 ,考虑约束扭转的薄壁梁单元刚度矩阵有相当好的精确度 ,可以用于薄壁杆件的静动力分析。     

新型截面耐撞梁及其冲击吸能性能分析

提出了一种类似泡沫填充结构的轻质高吸能内部加筋薄壁梁的截面型式(加筋薄壁梁),采用数值仿真技术,以初始冲击力峰值、总吸能、比吸能为指标分析了该截面型式梁的抗弯性能.与同等质量的空心方形梁和泡沫铝填充梁进行比较,发现加筋薄壁梁的吸能性能(或比吸能)显著提高.同时初始冲击力峰值也有大幅下降,说明这种加筋薄壁梁是新型保险杠的良好截面型式.     

含脱层损伤复合材料层合梁的冲击动力屈曲

针对含初始缺陷和脱层损伤的复合材料层合梁的轴向冲击动力屈曲问题进行了分析。基于Hamilton原理导出了考虑初始缺陷、轴向和横向惯性、横向剪切变形以及转动惯性影响时含脱层损伤复合材料梁的非线性动力屈曲控制方程;基于B-R准则,采用有限差分方法求解了受轴向冲击载荷作用下含脱层损伤复合材料梁的动力屈曲问题;讨论了冲击速度、初始几何缺陷、铺层角度以及脱层长度等因素对复合材料层合梁动力屈曲的影响。     

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress–strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.     

Non-linear stability analysis of imperfect thin-walled composite beams

The static non-linear behavior of thin-walled composite beams is analyzed considering the effect of initial imperfections. A simple approach is used for determining the influence of imperfection on the buckling, prebuckling and postbuckling behavior of thin-walled composite beams. The fundamental and secondary equilibrium paths of perfect and imperfect systems corresponding to a major imperfection are analyzed for the case where the perfect system has a stable symmetric bifurcation point. A geometrically non-linear theory is formulated in the context of large displacements and rotations, through the adoption of a shear deformable displacement field. An initial displacement, either in vertical or horizontal plane, is considered in presence of initial geometric imperfection. Ritz's method is applied in order to discretize the non-linear differential system and the resultant algebraic equations are solved by means of an incremental Newton-Rapshon method. The numerical results are presented for a simply supported beam subjected to axial or lateral load. It is shown in the examples that a major imperfection reduces the load-carrying capacity of thin-walled beams. The influence of this effect is analyzed for different fiber orientation angle of a symmetric balanced lamination. In addition, the postbuckling response obtained with the present beam model is compared with the results obtained with a shell finite element model (Abaqus).     

薄壁曲梁的稳定性研究进展

 曲梁是桥梁、建筑、船舶、航空和航天工程中常见的薄壁构件，根据外载荷与主曲率平面的关系，又被称为拱或水平曲梁．随着工程材料的日益发展，如复合材料、功能梯度材料的引入，曲梁的应用范围更加广泛，进一步推进了薄壁曲梁稳定性问题的研究．本文首先对薄壁梁结构的稳定性行为进行了分类．接着简述了薄壁构件的基本假设，对比了近几十年来薄壁曲梁的基本理论，针对复合材料薄壁曲梁，总结了相应的本构关系，并对各理论间存在的分歧进行了归纳．结合最新的薄壁曲梁研究，根据平衡法、能量法和虚位移（虚功）原理推导出控制微分方程，阐述了相应的求解方法，如解析法、半解析法和数值解法．为验证薄壁曲梁理论的准确性，曲梁承载能力试验验证尤为重要，但目前国内外相关研究还很少，亟待发展．最后讨论了现阶段薄壁曲梁研究的局限性和未来发展的方向．     

一种复合材料的大挠度曲梁单元

本文研究了加劲壳的非线性有限元分析方法,提出了一种梁元素来模拟加筋。该元素具有曲轴线,任意形状的薄壁剖面和任意铺层方式,与三维退化曲壳元素完全协调,相对于壳中面可以有偏心,所分析的结构可以是层合复合材料加劲壳或各向同性材料单层加劲壳。     

轴向受载的Bernoulli—Euler薄壁梁固有振动和稳定性的理论研究

通过直接求解轴向受载的单对称均匀Bernoulli-Euler薄壁梁单元弯扭耦合振动的运动微分方程,推导了其动态传递矩阵,讨论了轴向载荷的变化对薄壁梁弯扭耦合振动固有频率的影响,并由此得到零频率振动（弹性屈出）发生时相应的轴向载荷,数值结果表明本文方法在其适应范围内是精确有效的。     

Linear viscoelastic analysis of straight and curved thin-walled laminated composite beams

This paper is devoted to study the behavior, in the range of linear viscoelasticity, of shear flexible thin-walled beam members constructed with composite laminated fiber-reinforced plastics. This work appeals to the correspondence principle in order to incorporate in unified model the motion equations of a curved or straight shear-flexible thin-walled beam member developed by the authors, together with the micromechanics and macromechanics of the reinforced plastic panels. Then, the analysis is performed in the Laplace or Carson domains. That is, the expressions describing the micromechanics and macromechanics of a plastic laminated composites and motion equations of the structural member are transformed into the Laplace or Carson domains where the relaxation components of the beam structure (straight or curved) are obtained. The resulting equations are numerically solved by means of finite element approaches defined in the Laplace or Carson domains. The finite element results are adjusted with a polynomial fitting. Then the creep behavior is obtained by means of a numerical technique for the inverse Laplace transform. Predictions of the present methodology are compared with experimental data and other approaches. New studies are performed focusing attention in the flexural–torsional behavior of shear flexible thin-walled straight composite beams as well as for thin-walled curved beams and frames.     

A NEW SPATIAL THIN-WALLED BEAM ELEMENT INCLUDING TRANSVERSE AND TORSIONAL SHEAR DEFORMATION

基于Timoshenko梁及Benscoter薄壁杆件理论,建立了考虑剪切变形、弯扭耦合以及翘曲剪应力影响的空间任意开闭口薄壁截面梁单元. 通过引入单元内部结点,对弯曲转角和翘曲角采用三节点Lagrange独立插值的方法,考虑了剪切变形和翘曲剪应力的影响并避免了横向剪切锁死问题;借助载荷作用下薄壁梁的截面运动分析,在位移和应变方程中考虑了弯扭耦合的影响. 通过数值算例将该单元的计算结果与理论解以及商用有限元软件和其他文献中的数值解进行对比和验证,结果对比表明该薄壁梁单元具有良好的精度和收敛性.     

基于塑性铰理论的车身概念设计正碰分析与优化方法

在概念设计阶段,车身碰撞安全性能评价是一个难点问题,需要详细的结构模型,本文基于塑性铰理论提出采用梁单元简化模型对框架车身进行概念设计阶段的耐撞性评估和优化设计方法。首先,介绍了关于箱型截面薄壁梁弯曲特性研究的理论模型与计算过程,接着赋予梁单元塑性铰的特性,模拟薄壁梁变形,再对框架车身进行了碰撞仿真。将仿真结果与详细模型对比,以分析简化模型的精度及可靠性。最后,以此为基础对框架车身进行耐撞性优化。结果表明,该简化模型易于创建,且有较高的精度,可用于概念设计阶段梁结构的设计工作。     

Global and local behaviour based composite damping studies on thin-walled box structure

The local (plate)/global (beam) vibration and damping behavior of composite thin-walled box member subjected to vibratory environment are studied and presented in this paper. This investigation is carried out by the use of 3D beam and thin plate finite elements and the corresponding modal frequencies/damping values of composite box beam are predicted by modal strain energy method. Application examples illustrate the ability of the 3D beam and thin plate element to predict both local and global modal frequencies/damping of hollow box sections. The influence of L/h ratio, b/h ratio and ply angle on the frequency and loss factor of composite box beam is investigated. In addition, an attempt has also been made to investigate the effect of temperature on the composite damping characteristics of rectangular box type section.