基于弹性基础梁理论的复合材料薄壁圆柱壳屈曲承载力模型

提出一种复合材料薄壁圆柱壳轴压局部屈曲承载力计算模型。在梁弯曲变形平截面假定和小变形假定的基础上,提出复合材料层合梁抗弯刚度的计算方法;根据轴压下圆柱壳的几何对称性及受力对称性,将圆柱壳局部屈曲问题转化为轴向和环向壳带的弯曲变形问题。依据薄壳稳定理论,建立弹性基础上纵向壳带局部屈曲模型,得到了复合材料圆柱壳屈曲承载力解析公式。理论计算公式与经验工程计算公式相比,具有形式上的相似性,且得到的计算系数可直接求出,而非经验范围选取。对三种铺层的复合材料薄壁圆柱壳进行了轴压试验,结合文献试验数据对比,试验结果与理论预测值基本一致,满足工程精度要求,验证了模型的正确性。     

基于能量法的变截面层合管整体稳定承载力计算方法

为计算变截面层合管杆件整体稳定承载力,提出一种基于能量法的理论计算模型。采用基于三维梁理论的层合管等效抗弯刚度计算方法,计算了等截面段、变截面段的等效工程弹性系数。在考虑剪切变形的影响以及杆件变截面对轴压挠曲线函数影响的基础上,基于能量法推导了变截面杆整体稳定承载力解析公式。以NASA复合材料变截面杆为算例,进行了理论计算和有限元数值模拟,结果显示:同时考虑上述两因素的理论计算结果与有限元结果最为接近,剪切变形对临界承载力的修正可达10%以上,轴压挠曲线函数的变化对承载力的修正约为1%,可忽略。以锥长和锥角为参数,对变截面杆的承载力、体积和承载效率进行双参数分析,发现变截面对弯曲变形能的影响远大于对剪切变形性能的影响,采用变截面形式能够提高层合管承载效率,且一定锥长下存在承载效率最高对应的最优锥角。     

设有单根拉条滑动座连接檩条的稳定性分析

采用精确解析解方法研究了跨中设有拉条、与屋面板采用滑动座连接的檩条承受纯弯矩时的弯扭屈曲,檩条两端简支,屋面板对檩条提供均布弹性扭转约束,拉条提供侧向弹性支撑。求解得到了解析解,给出了檩条由对称屈曲转变为非对称屈曲对应的拉条门槛刚度的表达式,并讨论了檩条截面、跨度、扭转约束刚度大小、拉条刚度大小及拉条作用点高度等因素对门槛刚度和临界弯矩的影响。经过全范围算例计算,给出了临界弯矩简化表达式。研究发现,无论均布扭转约束多大,无拉条时檩条总是以一个正弦半波屈曲,从而呈现出与均布弹性地基上压杆的屈曲不一样的性质。     

压弯剪扭实腹型钢混凝土柱抗震性能试验研究

为研究型钢混凝土(SRC)柱在压弯剪扭复合受力状态下的抗震性能,以截面尺寸、型钢含钢率、纵筋配筋率、体积配箍率和栓钉位置为变化参数,完成了12根型钢混凝土柱和1根钢筋混凝土(RC)对比柱的压弯剪扭低周反复试验。观察了试件在复合受扭状态下的破坏形态,对比分析了各试件的滞回曲线、骨架曲线、刚度退化、耗能及延性性能。结果表明：在压弯剪扭受力状态下,所有试件均发生弯扭破坏;荷载-柱顶位移滞回曲线呈饱满的梭形,扭矩-扭转角曲线为捏拢的“S”形;增大截面尺寸和配筋率可有效提高SRC柱的抗扭和抗弯承载力;峰值荷载前,抗扭刚度的退化速率明显快于抗弯刚度的退化速率,增大型钢含钢率和配筋率可延缓SRC柱的刚度退化;SRC柱的抗弯耗能能力优于抗扭耗能能力,扭转延性大于弯曲延性;与方形截面相比,矩形截面具有更好的扭转变形能力;在工字钢翼缘上焊接栓钉可有效提高SRC柱的抗震性能;根据现行规范和试验数据,提出SRC柱构造设计的相关建议和扭转耗能退化的经验公式。     

任意非对称断面薄壁箱梁一维有限元分析

根据薄壁箱梁的实际支承特点,设置支承坐标系并在支承坐标系中建立变形协调的相容条件,针对任意非对称断面薄壁箱梁,导出了考虑拉(压)弯扭翘空间耦合分析的单元刚度矩阵及等效节点力公式。此外,提出了通过设置具有线刚度、转动刚度、扭翘刚度的假想弹簧单元,对薄壁箱梁的复杂约束条件进行处理的一般方法。所得到的刚度矩阵表明,只有当忽略翘曲变形对截面转角的影响时,轴向拉压才只与水平弯曲及竖向弯曲相耦合,而与约束扭转不再耦合。算例结果表明了分析方法的有效性。     

扶手椅型单壁碳纳米管的扭转和弯曲变形

实验提出了一种针对单壁碳纳米管的原子尺度有限元模型.利用该模型对(5,5)型扶手椅型单壁碳纳米管的扭转和弯曲变形过程进行了模拟,发现其屈曲的临界扭转和纯弯曲角度分别约为40°和20°,与扭转屈曲相比,该碳管更容易发生弯曲屈曲.当弯扭复合变形时发生屈曲后,卸载时壁面褶皱的回复比较缓慢.在某些情况下,碳管的局部势能的变化与经典连续介质力学理论不一致,对此本文结合原子势理论给出了模拟结果的原子尺度的解释.     

圆弧拱平面外弹性弯扭屈曲临界荷载分析

该文从采用经典平衡理论推导了双轴对称纯压、纯弯圆弧拱的平面外弯扭屈曲方程,给出了两铰圆弧拱的平面外屈曲荷载解析解,其中考虑了截面翘曲刚度、荷载作用位置等参数的影响。推导中进行适当的近似,使过程更加简化和直观。对3 种不同形式均布径向荷载的情况进行了讨论,并与有限元结果进行了对比。研究表明,3 种均布径向荷载中以静水压力作用下屈曲荷载最高,该文提出的双轴对称截面纯压、纯弯两铰圆弧拱的平面外屈曲荷载解析解与有限元数值解吻合良好。     

压杆轴力与轴向位移全过程曲线的近似表达式

考虑了几何缺陷、残余应力和材料塑性,采用大变形理论自编程序3D-Steel-Struct 对工字形压杆屈曲前后的变形曲线进行了研究.对非完善双轴对称工字形截面压杆进行了二阶弹性和二阶刚塑性的理论分析,推导了相应阶段的轴压力与变形之间的关系,构造了轴压力与跨中挠度和轴压力与轴向位移之间的解析表达式,并与数值解非常吻合.研究了压杆轴压延性随长细比的变化规律,提出了一个延性与长细比的近似表达式,并具有良好的精度.     

复合受扭实腹式型钢混凝土柱恢复力模型研究EI北大核心CSCD

为研究复合受扭作用下实腹式型钢混凝土柱的恢复力模型,考虑扭弯比、轴压比和剪跨比的影响,完成了9个实腹式型钢混凝土柱的拟静力加载试验,获取了扭矩-扭转角骨架曲线和滞回曲线,分析了扭弯比、轴压比和剪跨比等试验变化参数对其扭转滞回性能的影响。基于试验扭转骨架曲线和滞回曲线,提出以屈服点、峰值点和破坏点为特征点的三折线骨架曲线模型,同时对滞回规则进行简化,建立实腹式型钢混凝土柱复合受扭恢复力模型。结果表明:随着扭弯比的增大,试件破坏形态由弯曲破坏为主转为扭转破坏为主;扭弯比对实腹式型钢混凝土柱的抗扭承载力影响最大;在扭转骨架曲线特征参数计算时考虑了扭弯比、轴压比和剪跨比的影响,计算结果与实测结果吻合较好。提出的考虑卸载刚度退化影响的扭转恢复力模型,能较好地预测复合受扭作用下实腹式型钢混凝土柱的扭转滞回曲线,可为此类结构在压弯剪复合受扭作用下的弹塑性地震分析提供参考。     

对角槽钢加劲钢板剪力墙抗震性能试验研究

为研究大跨高比的对角槽钢加劲钢板墙结构,该文对3个1/3缩尺的钢板剪力墙试件进行了拟静力试验研究,包括一个拼接式钢板剪力墙和2个拼接式-对角槽钢加劲钢板剪力墙。试验结果表明钢板剪力墙有良好的耗能能力,对角加劲钢板墙滞回曲线饱满呈梭形。槽钢的两个翼缘与钢板连接,形成具有更大抗扭刚度闭口截面,在加载过程中避免了加劲肋的扭转而导致加劲效果降低。对角布置的槽钢加劲肋具有较大的抗弯刚度,在弹性阶段提高钢板的弹性屈曲荷载,限制钢板平面外变形;在弹塑性阶段能起到增大拉力带的作用,提高结构承载力。推导了框架柱的剪力、轴力和弯矩计算公式,结果表明对角槽钢加劲形式对边缘构件的附加轴力和剪力作用较大,因此在设计时应考虑加劲肋的支撑作用。     

基于双特征参数解的直杆弹性动力后屈曲研究

利用差分方法求解动力后屈曲非线性方程解，研究了弹性直杆的2类轴向碰撞屈曲问题．将双特征参数解得出的含有小幅值参数的初始动力屈曲模态作为非线性后屈曲解的初始条件．理论计算的结果与文献中的实验数据达到了很好的一致，由此验证了双特征参数方法的正确性．研究结果还揭示了碰撞过程中屈曲变形扩展和发展的机理，以及轴向应力波和屈曲变形的相互作用规律．     

复合材料层合夹芯板局部变形行为研究

在局部荷载作用下,带软夹芯层的夹芯板结构将产生一定的局部变形现象。本文采用双参数基础模型模拟软夹芯材料与受载层合面板间的相互作用,基于经典层合板理论,推导并给出了夹芯板结构局部变形问题的半解析分析方法,并通过算例讨论了边界条件、荷载作用方式、夹芯层厚度与弹性模量等因素对该类结构局部弯曲和局部屈曲行为的影响。     

On the mechanics of the global bending collapse of circular tubes under dynamic axial load—Dynamic buckling transition

The common features of the deformation of long circular tubes made from different aluminium alloys and subjected to various axial impact loadings are established and used to develop simplified structural models for global bending collapse and progressive buckling. A two-phase deformation model for axially loaded structural elements is proposed, which retains the characteristic features of the initial compression and subsequent bending/buckling phases. It is shown that the velocity histories in the two principal collapse modes of long tubes play an important role for the formation of the particular deformation pattern. The simplified structural models are verified with some numerical finite-element results and their behaviour is shown to be adequate.     

Mechanism of buckling development in elastic bars subjected to axial impact

By use of the finite difference method, the non-linear equations governing the elastic dynamic post-buckling deformations are solved for two types of impact buckling problems for straight bars. The initial dynamic buckling mode with a small amplitude parameter, given by the twin-characteristic-parameter solution, is used as the initial condition of the non-linear post-buckling solution. Particular attention is paid to the mechanism of growth and spread of buckling deformation in the bar and the interaction between the axial stress wave and the buckling deformation in the process of impact. It is found that the initial buckling deflection with one half-wave, occurring near the impacted end, spreads forward and develops into the higher mode as the axial stress wave propagates in the bar. The theoretical results are in good agreement with the experimental results reported in the literatures.     

The surface effect on the strain energy release rate of buckling delamination in thin film-substrate systems

Gurtin-Murdoch continuum surface elasticity model is employed to study the buckling delamination of ultra thin film-substrate system. The effects of surface deformation and residual stress on the large deflection of ultra thin film are considered in analysis. A concept of effective bending rigidity (EBR) for ultra thin plate is proposed on the basis of Gurtin-Murdoch continuum theory and the principle of minimum potential energy. The governing equations with EBR are formally consistent with the classical plate theory, including both small deflection and large deflection. A surface effect factor is introduced to decide whether there is need to consider the surface effect or not. Combining the buckling theory and interface fracture mechanics, we obtain analytical solutions of the critical buckling load and the energy release rate of the interface crack in the film-substrate system. It is seen that the surface deformation and residual stress have significant effects on the buckling delamination of ultra thin film-substrate system.     

考虑横向剪切效应时圆柱型正交各向异性球面扁壳在横向载荷作用下的非线性压屈

本文应用参考文献所介绍的修正迭代法探讨了横向载荷作用下,圆柱型正交各向异性圆底球面扁壳的非线性稳定同题,得出了这一同题的解析解。在求解过程中,本文放弃了经典板壳理论的Kirchhoff假定,从而考虑了横向剪应变对于弯曲变形的影响, 计算结果表明:本文的分析方法和结论是正确的;对于正交各向异性复合材料板壳而言,横向剪切效应是值得注意的。     

On rigid-elastic bending and buckling deformations of long beams

Summary. Localized bending and buckling of long beam-like straight films due to the change of stiffness is presented. A two-phase beam model is developed. The one phase is considered of infinite stiffness (rigid deformation). The localized phase is studied and the rigid deformation is defined. This kind of two–phase deformations may take place in thin surface structures such as films.     

Controllable deformations of elastic spatial rods

Summary The determination of all the statically controllable deformations for the classical Kirchhoff-Clebsch theory for three-dimensional deformations of elastic inextensible rods is considered. The analysis shows that the most general deformation is the case in which a rod initially in the shape of a helix is deformed into another helix. The case of planar bending with no twist is also shown to give results that can be obtained from the theory of the planar elastica.     

套管构件中轴压内核与柔性套筒线接触的屈曲

对套管构件中承受轴向压力的内核,提出了它与柔性套筒之间线接触屈曲的模型,研究了内核与套筒线接触的后续变形过程。利用小挠度二阶平衡微分方程推导了线接触屈曲后内核挠度、弯矩、剪力、接触力等物理量的计算公式。应用算例表明:(1)当内核与套筒刚度比值足够小时,内核在经历与套筒点接触、线接触的变形过程后,会发生线接触屈曲,最终演变成同侧两点接触变形;(2)当内核与套筒刚度比值足够大时,内核只经历与套筒点接触、线接触的变形过程,不发生线接触屈曲,最终内核与套筒一起发生失稳破坏。该模型也能应用于模拟内核与刚性套筒线接触的屈曲。     

A finite‐volume method for deformation analysis of woven fabrics

Efficient numerical methods for simulating cloth deformations have been identified as the key to the development of successful Computer‐Aided Design systems for clothing products. This paper presents the formulation of a new finite‐volume method for the simulation of complex deformations of initially flat woven fabric sheets under self‐weight or externally applied loading. The fabric sheet is assumed to undergo very large displacements and rotations but small strains during the process of deformation. The fabric material is assumed to be linear elastic and orthotropic. The fabric sheet is discretized into many small structured patches called finite volumes (or control volumes), each containing one grid node and several face nodes. The bending and membrane deformations of a typical volume can be defined using the global co‐ordinates of its grid node and surrounding face nodes. The equilibrium equations governing the complex deformations are derived employing the principle of stationary total potential energy. These equations are solved using a single‐step full Newton–Raphson method which is found to be capable of predicting the final deformed shape, the only result of interest in a fabric drape analysis. To speed up convergence, the line search technique is adopted with good effect. This single‐step approach is more efficient than the step‐by‐step incremental approach employed in conventional non‐linear finite element analysis of load‐bearing structures. A number of example simulations of fabric drape/buckling deformations are included in the paper, which demonstrate the efficiency and validity of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.