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对受压球壳进行特征值屈曲分析,得到了前6阶屈曲模态及线性屈曲临界载荷;采用弧长法进行非线性有限元分析,对理想球壳施加初始扰动,通过2次扰动值折半的方法求得引起结构屈曲的最小扰动值,追踪到了屈曲分支点和全过程载荷-位移路线。基于前6阶屈曲模态位移,在受压球壳中分别引入2.5mm和1mm两种缺陷值,分析缺陷对球壳屈曲特性的影响。结果表明:取壳厚的0.5%即0.05mm时,得最小扰动值,近似模型与完善结构极值载荷的差值为0.93%;球壳是缺陷敏感性结构,缺陷的幅值和分布都对其极限载荷有影响,缺陷幅值与厚度比为0.1时,缺陷球壳承载力相对理想结构下降了约11%,缺陷幅值与厚度比为0.25时,承载力相对下降了约30%,说明提高球壳稳定性需要提高球壳加工精度。 相似文献
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复合材料结构的动力屈曲研究进展 总被引:7,自引:0,他引:7
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 相似文献
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薄壳结构的屈曲通常对初始缺陷十分敏感,因此对几何初始缺陷的精确测量是高质量的壳体屈曲试验的必要环节。本研究旨在开发一套基于激光测距仪的初始缺陷测量系统,以实现对壳体结构的快速、精确、非接触的测量。本文详细介绍该系统的设计思想及实现方法,包括激光测距仪的选择、转动与直线运动的实现、数据采集与计算机自动控制技术等。利用该系统对两个柱支承钢筒仓模型进行了仔细的初始缺陷三维测量,验证了系统的适用性和可靠性。文中还提出了利用二重傅立叶分解技术分析实测缺陷的方法。本文成果与方法为薄壳结构屈曲试验奠定了基础。 相似文献
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采用带旋转自由度参数C^0类板(壳)单元,研究复合材料箱型结构的初始屈曲性态,在推导单元几何刚度阵时,同时考虑出平面位移和面内位移对膜应变的影响;着重讨论了不同材料正方形截面梁的长细比与欧拉临界力的关系,复合材料典型盒段的截面形式和铺设角,铺设次序对初始屈曲性态的影响。 相似文献
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利用随机场对圆柱薄壳结构的初始几何缺陷进行建模,并据此建立了一种用于含初始几何缺陷轴压圆柱薄壳屈曲分析的随机分析方法。首先,指出已有将圆柱薄壳初始几何缺陷表征为二维高斯随机场的方法会导致与实际不相符的初始几何缺陷,如圆柱周长显著增大或缩小的几何缺陷。其次,提出一种考虑周长不变约束的随机场建模方法,以剔除与实际不相符的随机几何缺陷。最后,基于所建立的初始几何缺陷随机场模型,利用非干涉多项式混沌展开法进行圆柱薄壳的随机屈曲分析,给出临界屈曲载荷的概率分布。数值试验结果表明,基于随机场理论的初始几何缺陷建模方法可有效刻画几何缺陷对结构承载能力的影响,而提出的约束随机场建模方法又能有效减小结果的分散性。 相似文献
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针对薄壁圆筒壳结构轴压屈曲载荷的缺陷敏感性以及真实几何缺陷的不确定性,提出一种基于实测缺陷数据和极大熵原理的初始缺陷建模与屈曲载荷预测方法。首先,将初始几何缺陷视为二维随机场,并利用实测缺陷数据和Karhunen-Loève展开法将初始缺陷的随机场建模转化为随机向量的建模;其次,利用极大熵方法确定随机向量的概率分布;最后,基于所构建的初始缺陷随机模型,利用MCMC抽样方法和确定性屈曲分析方法,进行随机屈曲分析并给出基于可靠度的屈曲载荷折减因子。数值算例表明,与直接假设随机场相关结构的方法相比,本文方法的结果是对薄壁圆筒壳屈曲载荷的一个更无偏估计。 相似文献
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Detailed experimental studies are performed on the postbuckling behavior of circular cylindrical shells under hydrostatic pressure, by using lap-jointed polyester test cylinders with radius 100 mm, thickness 0.25 mm and lengths ranging from 23 to 165 mm. Connections of the edge shortening and radial displacement with applied pressures as well as wave forms for typical postbuckling configurations are determined for various values of the shell curvature parameterZ ranging from 20 to 1000. It is found that the buckling pressure and the corresponding wave number for each cylinder compare favorably with those theoretically predicted, and that the minimum pressure after buckling decreases with the increase inZ, until it becomes about 70 percent of the theoretical buckling pressure for long shells withZ greater than 200. 相似文献
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用实验及数值模拟方法研究了电磁内爆套筒的屈曲响应规律。用电容器组脉冲发生器装置作为驱动源,设计4种不同材料、不同尺寸的金属套筒,通过调节电容器组的充电电压得到不同的加载电流,研究材料及几何参数、加载脉冲特性对套筒屈曲的影响;采用瞬态非线性有限元方法对实验结果进行了数值模拟。研究表明,在同样加载电流作用下相同材料套筒形成的屈曲波数随半径/厚度比增大而增大,不同材料套筒的屈曲波数随屈服强度/塑性强化模量比值增大而增大,而相同材料的屈曲波数不随加载电流的大小而改变;模拟计算结果与实验结果基本吻合。 相似文献
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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 相似文献
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The structural instability of multi-walled carbon nanotubes (MWCNTs) has captured extensive attention due to the unique characteristic of extremely thin hollow cylinder structure. The previous studies usually focus on the buckling behavior without considering the effects of the wall number and initial pressure. In this paper, the axial buckling behavior of MWCNTs with the length-to-outermost radius ratio less than 20 is investigated within the framework of the Donnell shell theory. The governing equations for the infinitesimal buckling of MWCNTs are established, accounting for the van der Waals (vdW) interaction between layers. The effects of the wall number, initial pressure prior to buckling, and aspect ratio on the critical buckling mode, buckling load, and buckling strain are discussed, respectively. Specially, the four-walled and twenty-walled CNTs are studied in detail, indicating the fact that the buckling instability may occur in other layers besides the outermost layer. The obtained results extend the buckling analysis of the continuum-based model, and provide theoretical support for the application of CNTs. 相似文献
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An experimental and numerical study was performed on the buckling behavior of clamped-free truncated cones under external pressure. A lap-jointed polyester cone was vertically settled in a water vessel and was clamped at the small radius end. Raising water level, the relation of normal displacement with water level was recorded and the buckling water level was determined. The experimental results were in good agreement with the finite-element solutions. The same finite-element program was then used for a parametric study on the buckling of clamped-free cones subjected to uniform external pressure. The results show that the ratio of the critical external pressure of a clamped-free cone with that of a simply supported equivalent cylinder is a function of only the taper ratio ψ of the cone. 相似文献
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M. R. S. C. Bose G. Thomas R. Palaninathan S. P. Damodaran P. Chellapandi 《Experimental Mechanics》2001,41(2):144-150
This paper presents the results of an experimental study on the buckling of scaled-down models of the inner vessel used in
nuclear reactor structures. The inner vessel, a shell of composite geometry, consists of two cylindrical shells connected
by conical and torus shells. There are six stand-pipes on the conical portion of the vessel carrying heat exchangers and pumps.
Scaled-down models of the inner vessel are made by the conventional fabrication methods (rolling, welding) and are tested
in the present study. The test setup consists of a loading system for applying concentrated load on the stand-pipes, an air
compressor for applying internal pressure and the related instrumentation. Imperfection scans are carried out in a specially
fabricated experimental setup using linear variable differential transformers (LVDTs) before and during loading. Using the
scanned raw data, the initial geometric imperfections and eccentricity between the LVDTs and the specimen axes at different
axial locations are calculated. The results show that the maximum initial imperfections are on the order of 1.75 times the
wall thickness; generally, the growth of deformation patterns with loading resembles the shapes of initial imperfections,
and the growth is predominant on lower cylinder and torus regions. The general purpose, finite element-based software, ABAQUS,
is used to obtain the analytical values. The initial imperfections measured on the experimental models are incorporated into
the finite element models. The agreement between experimental and analytical buckling loads is within about 30 percent error. 相似文献