水下爆炸载荷作用下环肋加筋圆柱壳结构的弹塑性动力屈曲

为研究水下爆炸载荷作用下潜艇结构的动力屈曲现象,以潜艇耐压结构的简化模型环肋加筋圆 柱壳结构为研究对象,建立流固耦合有限元分析模型,应用瞬态有限元分析程序MSC.Dytran对该结构在水 下爆炸冲击载荷作用下的弹塑性动力屈曲行为进行研究,基于Budiansky-Roth准则和Southwell方法确定环 肋加筋圆柱壳结构的临界屈曲载荷,讨论结构动力屈曲的影响因素如载荷强度、网格密度、径厚比、长径比、加 筋截面间距、加筋尺寸等对环肋加筋圆柱壳结构动屈曲模态和临界屈曲载荷的影响。结果表明:采用建立的 流固耦合有限元分析模型,应用动力瞬态有限元软件MSC.Dytran可以对加筋圆柱壳结构的动力屈曲行为进 行模拟,模型网格尺寸大小、结构几何参数对结构的动力屈曲临界载荷都有一定的影响,其中加筋圆柱壳结构 的径厚比对结构的动力屈曲临界载荷影响最为显著。     

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。     

考虑强度与固化变形的复合材料加筋壁板铺层优化方法

加筋壁板是复合材料飞行器主承力构件的主要结构形式,通过复合材料铺层参数设计可以有效优化壁板的强度,但铺层参数的变化也会影响壁板的固化变形.因此,复合材料加筋壁板铺层设计过程中需要综合考虑整体强度和固化变形.本文针对复合材料加筋壁板结构,建立了失效分析模型和固化变形分析模型;基于实验设计方法、NSGA-Ⅱ遗传算法以及上述分析模型,建立了综合考虑强度与固化变形的加筋壁板铺层优化方法.优化结果显示复合材料加筋壁板在强度提高的同时,固化变形显著降低.     

新的复合材料格栅加筋板的平铺等效刚度法

针对薄壁复合材料格栅加筋结构的受力特点,在改进原有力学假设的基础之上,推导了一种新的平铺等效刚度计算方法,它充分考虑了筋条和面板之间的相互作用.通过格栅单元结构布局形式的参数化表示,建立了通用的力学分析模型;该模型可用于分析各种结构布局形式和面板铺层方式下的结构总体屈曲问题,故对于航空航天结构设计非常有用.结合Rayleigh-Ritz方法,推导出了求解格栅加筋板屈曲载荷的通用线性特征方程;最后,分析了多种类型格栅结构的算例,并与现有的各种方法进行了比较,结果更为精确,因而对格栅加筋结构的优化设计具有很好的应用价值.     

具有分层损伤的不同加筋形式复合材料层合板的后屈曲性态研究

基于板的一阶剪切理论和V on-K arm an大挠度理论,分别推导了复合材料层合板和层合梁的几何非线性有限元列式,提出了含嵌入分层的复合材料加筋层合板在受压缩载荷作用下的后屈曲有限元分析方法,对在板厚方向具有不同分层位置的加筋板结构进行了有限元数值分析,研究了不同的加筋方式及筋的分布对具有分层损伤的复合材料加筋层合板的后屈曲性态的影响,所得结果对确定在压缩载荷作用下含损伤复合材料加筋层合板的剩余承载能力具有参考价值。     

复合材料结构的动力屈曲研究进展

本文系统地回顾了复合材料结构的动力屈曲研究进展，对周期性动载荷和瞬态动载荷作用下，复合材料结构的动力屈曲作了阐述；讨论了耦合效应，横向剪切变形、初始几何缺陷以及铺层方式等因素对动力屈曲的影响；就复合材料结构动力屈曲研究的发展前景提出了一些有益的建议     

轴压加筋板壳的弯扭稳定性分析

以统一的方式分析了轴压加筋板壳的弯扭稳定性.根据小挠度能量法,采用了约束剪心概念并考虑了加筋条偏心距,截面的翘曲刚度及剪心和形心间位置偏差等因素的影响,推导了屈曲方程。例题计算的结果表明了所提出方法的可行性。     

基于蚁群算法的复合材料缠绕壳体铺层顺序优化

为了提高纤维复合材料缠绕壳体结构的屈曲稳定性,本文将蚁群算法(ACA)求解旅行商问题(TSP)的方法引入到缠绕层顺序优化的计算中.阐明铺层顺序优化的本质是调整沿板厚方向的刚度分布以提高版的抗弯刚度,同时改善荷载的传递路径,以降低由偏心而产生的附加弯矩,从而提高结构的抗屈曲能力;扩展了经典蚁群算法,提出一种分组编解码方法...     

屈曲前变形对加筋圆柱曲板侧压稳定性的影响(线性一致理论)

一、前言航空结构中,经常遇到加筋园柱曲板在侧压作用下的稳定问题。曾有许多作者[1],[2],[3],[4]研究过加筋园柱壳的弹性稳定问题,并讨论了加筋偏心的影响。[4]还考虑了屈曲前变形的影响。我们曾在[5],[6]中讨论过简支园柱曲板的侧压稳定问题。[5]是将曲板作为各向异性板处理,[6]考虑了加筋离散性的影响。但是,[5][6]均假定屈曲前,曲板为薄膜应力状态。由于简支园柱曲板,在侧压作用下,屈曲前已有弯曲变形,并非薄膜应力状态,因而理论分析与实      

剪切载荷下加筋板失稳模态的全场数字光学测试

通过全场光学测试和应变测试的方法,研究了剪切载荷下平板、加筋板、含切口加筋板的屈曲模态及极限承载能力。实验采用对角拉伸方式施加剪切载荷,运用全场光学形貌扫描方法对试件的变形形貌和屈曲模态进行实时扫描。实验结果表明:采用光学方法得到的加筋板试件的临界屈曲载荷值(12.44 k N)与应变测量结果(12.65 k N)吻合较好,此方法可用于临界屈曲载荷的测试;平板试件破坏时的屈曲模态沿加载方向对称分布,完整加筋板与中心切口加筋板屈曲模态均呈反对称分布,而侧切口加筋板试件的屈曲模态没有对称性;加强筋的强化和切口的局部损伤会引起屈曲模态的偏移;加筋板试件在发生破坏前的位移-载荷曲线均相近;中心切口会极大地削弱加筋板的极限承载能力。     

轴压层合结构脱层屈曲及其扩展研究进展

脱层及其进一步扩展可以降低层合结构的强度．首先简单介绍了脱层的一般概念、起因及其分类．从一维脱层、二维脱层和柱壳脱层三个方面介绍了脱层问题的研究概况．指出拉弯耦合和横向剪切效应对脱层结构的屈曲载荷和后屈曲特性影响很大;对于不同的材料特性和尺寸比率,脱层结构的屈曲模态和最终承载能力也不同．最后提出了需进一步深入研究的问题      

在径向载荷和轴向冲击联合作用下的圆柱壳塑性稳定性分析

对有径向载荷的圆柱壳，受轴向冲击时塑性失稳的临界速度进行理论分析。分析结果与实验值相吻合，并给出一般的规律，它也适用于无径向载荷的情况。     

On stability of cylindrical shells of variable thickness with initial imperfections

The paper outlines a numerical method for stability analysis of cylindrical shells with initial imperfections. We solve a nonlinear buckling problem for a cylindrical shell with variable wall thickness under surface pressure. The imperfections of the shell are modeled as the first buckling mode. A probabilistic approach is used to determine the reliability against buckling of the cylindrical shell with the probability density of initial imperfections represented by uniform distribution, triangular distribution, or Gaussian distribution     

易拉罐在轴-侧-扭-内压联合作用下的屈曲地貌

柱壳结构广泛应用于各个领域, 但由于其对初始缺陷较为敏感, 容易发生灾难性的屈曲失稳. 本文利用非线性有限元分析程序ABAQUS研究了柱壳屈曲问题, 并应用到了易拉罐的屈曲分析. 首先采用数值模拟的方法验证了Virot等学者的易拉罐屈曲试验结果, 然后为了获得屈曲的一些普适结果, 进一步考察了柱壳的屈曲表现. 对柱壳结构在不同载荷组合、不同几何参数作用下进行了细致分析. 为了讨论的直观, 本文绘制了柱壳结构在受到侧压-轴压载荷作用下外力-屈曲载荷-位移三维屈曲地貌图(称为landscape). 结果表明: 在侧压-轴压-扭转载荷作用下, 试件力-位移曲线出现了"cliff"(断崖)现象; 扭转载荷的施加不利于试件整体稳定性, 并造成了试件对初始缺陷的敏感性; 对于受到轴压-扭转载荷作用的试件, 本文定义承载力为零的平面为"sea level"(海平面)来区分试件破坏模式; 通过对不同边界条件的试件进行分析, 发现试件两端固定可以有效地增加结构的承载能力, 提高稳定性. 对柱壳结构内部充气可以大幅度提升结构的承载能力和稳定性, 减小对初始缺陷的敏感度.      

弹性圆柱壳在轴向冲击载荷和温度耦合作用下的屈曲

通过引入哈密顿体系,将临界载荷和临界温度及它们所对应的屈曲模态归结为辛体系下的广义本征值和本征解问题。根据辛本征解的正交性和完备性,给出了全部的且独立存在的屈曲模态。数值结果表明,在轴向冲击载荷和温度耦合作用下,弹性圆柱壳的屈曲呈现出复杂的模式,温度直接影响冲击临界载荷的大小。随着温度的增加,冲击临界荷载降低,最后,文中给出各种条件下的屈曲模态。     

Stability of open circular cylindrical shells reinforced with longitudinal ribs

We obtain exact and approximate solutions to buckling problems for circular cylindrical open shells hinged at all edges and quasiregularly reinforced with discrete longitudinal ribs. It is shown that analogous solutions to natural-vibration problems for such shells can easily be found Translated from Prikladnaya Mekhanika, Vol. 44, No. 12, pp. 83–92, December 2008.     

前屈曲应力状态对组合加肋旋转壳失稳临界压力影响的探讨

推导了包含前屈曲弯矩和横剪力的旋转壳弹性稳定性基本方程.运用Riccati传递矩阵法对组合加肋旋转壳算例进行了稳定性分析,并与假设前屈曲状态为薄膜应力状态计算出的失稳临界压力进行了比较.结果表明,前屈曲弯矩和横剪力对组合加肋旋转壳失稳临界压力的影响较小,随着壳板厚度和肋骨尺寸的增大及肋骨间距的缩短,影响略有增大.因而,分析组合加肋旋转壳弹性稳定性时,前屈曲状态采用薄膜应力状态的假设是合理的.     

Nonlinear stability of thin elastic cylinders of different length under global bending

Many thin-walled cylindrical shells are used in structural applications in which the dominant loading condition is global bending. Key examples include chimneys, wind turbine support towers, pipelines, horizontal tanks, tubular piles and silos. The buckling behaviour of these structures in bending is complex due to the coupling between cross-section ovalisation and local bifurcation buckling. Analytical treatments of this problem have a history going back almost a century and still constitute an active and challenging research area.This paper investigates in detail the effect of cylinder length on the nonlinear elastic buckling behaviour of clamped cylindrical tubes under global bending, covering a very wide range of lengths. It is found that the behaviour may be classified into four distinct length-dependent domains with clearly-defined boundaries which have here been assigned the names ‘short’, ‘medium’, ‘transitional’ and ‘long’. Algebraic characterisations of the computed nonlinear moment–length relationships are proposed for design purposes.     

Buckling of yeast modeled as viscoelastic shells with transverse shearing

Yeast cells can be regarded as micron-sized and liquid-filled cylindrical shells. Owing to the rigid cell walls, yeast cells can bear compressive forces produced during the biotechnological process chain. However, when the compressive forces applied on the yeast go beyond a critical value, mechanical buckling will occur. Since the buckling of the yeast can change the networks in its cellular control, the experimental research of the buckling of the yeast has received considerable attention recently. In this paper, we apply a viscoelastic shell model to study the buckling of the yeast. Meanwhile, the turgor pressure in the yeast due to the internal liquid is taken into account as well. The governing equations are based on the first-order shear deformation theory. The critical axial compressive force in the phase space is obtained by the Laplace transformation, and the Bellman numerical inversion method is then applied to the analytical result to obtain the corresponding numerical results in the physical phase. The concepts of instantaneous critical buckling force, durable critical buckling force, and delay buckling are set up in this paper. And the effects of the transverse shear deformation and the turgor pressure on the buckling phenomena are also given. The numerical results show that the transverse shearing effect will decrease the instantaneous critical buckling force and the durable critical buckling force, while the turgor pressure will increase both of them.     

Torsional,flexural, and torsional-flexural buckling modes of a cylindrical shell under combined loading

Stability problems for cylindrical shells under various loading modes were considered in numerous papers. A detailed analysis of such problems can be found, e.g., in the monograph [1]. We refer to the solutions presented in this monograph as classical.For long cylindrical shells in axial compression, one of the buckling modes is the purely beam flexural mode similar to the classical buckling mode of a straight rod. It is well known that it can be studied by using the nonlinear or linearized equations of the membrane theory of shells. In [2], it was shown that, on the basis of such equations constructed starting from the noncontradictory version of geometrically nonlinear elasticity relations in the quadratic approximation [3], under the separate action of the axial compression, external pressure, and torsion, there are also previously unknown nonclassical buckling modes, most of which are shear ones.In the present paper, we show that the use of the above equations for cylindrical shells under compression and external pressure with simultaneous pure torsion or bending permits revealing the earlier unknown torsional, beam flexural, and beam torsional-flexural buckling modes, which are nonclassical, just as those found in [2]. The second of these buckling modes is realized when axially compressing forces are formed in the shell with simultaneous torsion, and the third of them is realized under compression combined with pure bending.It was found that, earlier than the classical buckling modes, the torsional buckling modes can be realized for relatively short shells with small shear rigidity in the tangent plane, while the second and third buckling modes can be realized for relatively long shells.