MT300/KH420碳纤维/聚酰亚胺树脂复合材料层合圆柱壳高温承载性能

基于Donnell-Mushtali近似理论及热弹性理论,考虑结构热变形和材料高温性能衰减等温度影响因素,对MT300/KH420碳纤维/聚酰亚胺树脂复合材料圆柱壳在常温、420℃及周向210~420℃不均匀温度场等热载工况下的承载性能进行了理论分析。并引入一阶屈曲模态缺陷作为几何初始扰动,利用ABAQUS,采用非线性显式动力学方法完成对MT300/KH420复合材料圆柱壳在以上热载工况下的轴压稳定性有限元仿真计算,计算结果与理论分析较为一致。设计并开展MT300/KH420复合材料圆柱壳力-热载荷联合轴压试验,获得圆柱壳在以上热载工况下的破坏载荷和破坏模式。研究表明:高温工况下,力学性能衰减和温场不均匀引起的结构热变形是影响MT300/KH420复合材料圆柱壳轴向失稳载荷的主要因素。      

复合材料圆柱壳的非线性稳定性分析

本文应用能量变分方法,对加筋多层的复合材料圆柱壳,进行了非线性稳定性分析,处理了均匀轴压和横向载荷两种载荷情况。文中用卡门-佟聂耳方程考虑了柱壳失稳时的几何非线性影响,同时通过剪切模量的非线性变化考虑了复合材料的物理并线性影响。本文也分析了初始缺陷对于屈曲特性的影响。文中具体计算了硼/环氧圆柱壳失稳的数值算例。分析和计算表明,材料的剪切非线性和初始缺陷的几何非线性对圆柱壳的屈曲特性有着显著的影响。     

纤维缠绕圆柱壳轴压稳定性

本文系统地讨论了多层复合材料圆柱壳在轴向压缩载荷条件下的轴压稳定性。基于 Donnell 方程,将位移法与复数解法推广应用于纤维缠绕圆柱壳的轴压稳定性问题,考虑了八种边界条件,提出了壳体的前屈曲理论解以及屈曲模态,临界载荷的算法,特别着重考虑了各类边界条件与耦合效应。其理论和结果可直接应用于固体火箭发动机壳体的结构设计。     

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。     

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。     

径向载荷作用下复合材料圆柱壳的非线性动力屈曲

采用半解析法求解径向阶跃载荷作用下复合材料圆柱壳的非线性动力屈曲。基于一阶剪切变形理论，由Hamilton原理推导出包含横向剪切变形以及几何初缺陷的圆柱壳的非线性动力方程，位移及载荷沿周向采用级数展开，由Galerkin方法得到微分方程组，通过有限差分法求解；根据响应情况，由B—R准则判定屈曲，确定屈曲临界载荷。     

脱胶缺陷尺寸对复合材料加筋板屈曲及后屈曲特性的影响

为确定脱胶缺陷对复合材料加筋板屈曲及后屈曲特性的影响,对含不同脱胶缺陷工型筋条的复合材料加筋板进行了压缩试验研究。结果表明,30 mm和50 mm的缺陷对试验件承载能力影响很小,当缺陷尺寸增至80 mm时,试验件后屈曲承载能力明显下降。借助超声检测技术对缺陷的扩展行为进行了监测,结果表明,当压缩载荷达到破坏载荷的85.3%时,预制缺陷的对角位置处出现扩展迹象。通过影像云纹法获得两半波和三半波失稳模态的形成过程。对失稳模态的监测结果还表明,随缺陷长度增加,该型加筋板的失稳模态从三半波向两半波转换。在试验基础上,利用ABAQUS软件建立有限元（FE）模型,依次进行了屈曲及后屈曲过程的数值模拟。屈曲分析用于获得试验件的失稳载荷及模态,在后屈曲分析中将失稳波形以几何扰动的形式引入FE模型,最终计算结果与试验结果基本吻合,表明该模型可以用于复合材料加筋板屈曲及后屈曲性能的预测。     

复合材料翼面壁板轴压稳定性

基于T型长桁铺层数不同的两块复合材料翼面加筋壁板试件SC-1和SC-2,开展轴压稳定性试验研究,并提出一种预测屈曲载荷及最小后屈曲承载能力的工程分析方法,结合有限元特征值屈曲分析方法、有限元弧长法对试件的屈曲载荷、屈曲模态及后屈曲承载能力进行分析。试验结果表明,铺层数较多的试件SC-1的蒙皮局部屈曲应变较高,壁板也具有更高的屈曲载荷。在后屈曲阶段,SC-2加载到试验屈曲载荷的2.4倍未发生材料破坏和长桁蒙皮间脱粘损伤。工程分析方法和特征值屈曲分析能够准确预测壁板的屈曲载荷,最大误差分别为-9.3%和-2.8%,工程分析得到SC-2的最小后屈曲承载能力为试验屈曲载荷的2.09倍。有限元弧长法分析得到两件试件的屈曲载荷误差均小于1%,并具有壁板轴压屈曲模态预测和变形跟踪能力。      

纤维增强复合材料薄壁圆管扭转失效分析

对碳纤维增强树脂基复合材料（CFRP）薄壁圆管的扭转屈曲、失效载荷和失效模式进行了试验和数值模拟。试验观察圆管在扭矩作用下的3种失效模式,分析了不同失效模式的特征和机理。考虑圆柱壳的初始缺陷和非线性屈曲等因素,利用ABAQUS建立了圆管屈曲和损伤的有限元模型。结果表明:屈曲诱发圆管表面微裂纹的产生和扩展,对圆管的失效有着加速作用;扭转失效过程中圆管层间应力较低,层间分层主要由管壁突然的破坏产生;圆柱壳的初始缺陷对屈曲和失效载荷的模拟影响较大,本文通过对比计算结果和试验数据确定了圆管的初始缺陷系数;损伤模型的数值模拟结果与试验数据相一致,验证了有限元模型的有效性。      

加筋复合材料圆柱壳的屈曲和初始后屈曲的研究

本文分析了筋和壳的儿何参数及壳的铺层对纵向或环向密加筋的复合材料层合圆柱壳在轴压和侧压下的稳定性和初始后屈曲性能的影响。初始后屈曲分析基于Koiter理论。对几种不同几何参数、壳体铺层和载荷情况的加筋壳的计算表明:在所有情况下,外加筋比内加筋更有效地提高了屈曲载荷;复合材料壳的加筋效率一般都高于各向同性材料加筋壳;壳体的铺层对屈曲和初始后屈曲性能有很大影响。     

The use of initial imperfection approach in design process and buckling failure evaluation of axially compressed composite cylindrical shells

Thin-walled cylindrical shells are susceptible to buckling failures caused by the axial compressive loading. During the design process or the buckling failure evaluation of axially-compressed cylindrical shells, initial geometric and loading imperfections are of important parameters for the analyses. Therefore, the engineers/designers are expected to well understand the physical behaviours of shell buckling to prevent unexpected serious failure in structures. In particular, it is widely reported that no efficient guidelines for modelling imperfections in composite structures are available. Knowledge obtained from the relevant works is open for updates and highly sought. In this work, we study the influence of imperfections on the critical buckling of axially compressed cylindrical shells for different geometries and composite materials (Glass Fibre Reinforced Polymer (GFRP), Carbon Fibre Reinforced Polymer (CFRP)) and aluminium using the finite element (FE) analysis. Two different imperfection techniques called eigenmode-affine method and single perturbation load approach (SPLA) were adopted. Validations of the present results with the published experimental data were presented. The use of the SPLA for introducing an imperfection in axially compressed composite cylindrical shells seemed to be desirable in a preliminary design process and an investigation of a buckling failure. The knockdown factors produced by the SPLA were becoming attractive to account for uncertainties in the structure.     

轴压圆柱钢薄壳稳定设计综述

轴压圆柱薄壳广泛应用于土木工程中的各类钢壳结构,包括筒仓、塔桅、烟囱及容器等。轴压圆柱壳的屈曲问题一直是壳体稳定研究中最为活跃的课题之一。本文全面总结轴压圆柱壳稳定设计方面的研究成果及设计准则。首先简要回顾轴压圆柱壳的弹性经典解及初始缺陷敏感性的经典研究,接着对实际结构中的初始缺陷与制作过程的关系以及焊接残余应力对屈曲强度影响的近期研究进展进行了总结。然后,在简单介绍欧洲钢结构协会规程对轴压圆柱壳稳定设计有关规定的基础上,详细说明了新的欧洲钢壳设计规范所给出的设计准则及相应的研究背景。     

Buckling of Cracked Laminated Composite Cylindrical Shells Subjected to Combined Loading

A series of finite element analysis on the cracked composite cylindrical shells under combined loading is carried out to study the effect of loading condition, crack size and orientation on the buckling behavior of laminated composite cylindrical shells. The interaction buckling curves of cracked laminated composite cylinders subject to different combinations of axial compression, bending, internal pressure and external pressure are obtained, using the finite element method. Results show that the internal pressure increases the critical buckling load of the CFRP cylindrical shells and bending and external pressure decrease it. Numerical analysis show that axial crack has the most detrimental effect on the buckling load of a cylindrical shell and results show that for lower values of the axial compressive load and higher values of the external pressure, the buckling is usually in the global mode and for higher values of axial compressive load and lower levels of external pressure the buckling mode is mostly in the local mode.     

受轴压黏弹性层合圆柱壳的极值点蠕变失稳

基于Donnell薄壳理论, 采用准弹性方法, 分析了含初始几何缺陷黏弹性层合圆柱壳极值点形式的延迟失稳特征。由轴向缩短量的突然增加定义失稳临界时间, 对玻璃纤维/环氧树脂层合圆柱壳进行了数值计算。结果表明: 圆柱壳存在临界时间趋于无穷的持久临界荷载; 表征延迟失稳程度的瞬时弹性临界荷载与持久临界荷载之差值随着初始几何缺陷的增加而减小; 边界条件、 铺设方式对延迟失稳的影响机制可通过对应弹性层合圆柱壳的缺陷敏感性分析来考察。      

Experimental investigations on buckling of cylindrical shells under axial compression and transverse shear

This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision forin-situ measurement of the initial geometric imperfections. The shell models are made by rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections δ_max are of the order of ±3t (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through finite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen influences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.     

Nonlinear behavior and buckling of cylindrical shells subjected to localized external pressure

Buckling loads and postbuckling behavior of cylindrical shells subjected to localized external pressure are considered. The modified extended Kantorovich method with path-tracing technique is applied to determine the buckling loads of the cylindrical shells. It is found that the load is dependent nonmonotonically on geometrical parameters of the area subjected to external pressure. Respective postbuckling shapes show correlation with the shapes corresponding to secondary bifurcation paths for the cases of a cylindrical shell under uniform external pressure and a cylindrical shell under uniform axial load.     

Nonlinear dynamic buckling of functionally graded cylindrical shells subjected to time-dependent axial load

This paper is presented to solve the nonlinear dynamic buckling problem of a new type of composite cylindrical shells, made of ceram/metal functionally graded materials. The material properties vary smoothly through the shell thickness according to a power law distribution of the volume fraction of the constituent materials. The dynamic axial load is set in a linear increase form with regard to time. By taking the temperature-dependent material properties into account, the effect of environmental temperature rise is included. The nonlinear dynamic equilibrium equation of the shell was obtained by applying an energy method, and was then solved using the four-order Runge–Kutta method. The critical condition was eventually determined using B-R dynamic buckling criterion. Numerical results show the dynamic buckling load is higher than its static counterpart. Meanwhile, various effects of the inhomogeneous parameter, loading speed, dimension parameter, environmental temperature rise and initial geometrical imperfection on nonlinear dynamic buckling are discussed.     

Postbuckling of functionally graded fiber reinforced composite laminated cylindrical shells, Part I: Theory and solutions

Buckling and postbuckling behavior are presented for fiber reinforced composite (FRC) laminated cylindrical shells subjected to axial compression or a uniform external pressure in thermal environments. Two kinds of fiber reinforced composite laminated shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The governing equations are based on a higher order shear deformation shell theory with von Kármán-type of kinematic non-linearity and including the extension-twist, extension-flexural and flexural-twist couplings. The thermal effects are also included, and the material properties of FRC laminated cylindrical shells are estimated through a micromechanical model and are assumed to be temperature dependent. The non-linear prebuckling deformations and the initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths of FRC laminated cylindrical shells.     

复合材料波纹夹层圆柱壳设计及轴压性能

结构轻量化是航空航天发展的永恒主题, 波纹夹层圆柱壳作为常见的轻质结构形式, 在航空航天领域具有很大的发展空间。采用模具热压法, 制备出纵向和环向碳纤维复合材料波纹夹层圆柱壳, 其中芯子整体成型, 面板分瓣制备。采用经典板壳屈曲理论, 分析纵向和环向波纹夹层圆柱壳的轴压力学性能, 得到了欧拉屈曲、整体屈曲、局部屈曲和面板压溃4种失效模式下的极限载荷理论公式。绘制出结构的失效机制图, 直观显示出了失效模式与试件尺寸之间的关系。通过对纵向和环向波纹夹层圆柱壳的轴向压缩试验, 获得了结构的载荷-位移曲线及局部屈曲和面板压溃2种失效模式。结果表明:纵向波纹夹层圆柱壳的轴向承载能力及载荷/质量效率优于环向波纹夹层圆柱壳, 在一定范围内增加圆柱壳面板的厚度、减小圆柱壳的高度可提高结构的载荷/质量效率。