碟形封头在外压作用下的屈曲分析

采用有限元法分析了碟形封头在外压作用下的屈曲问题。通过静力学分析观察碟形封头内部的应力分布情况以判断封头发生屈曲的位置,并使用Newton—Raphson法和弧长法对封头进行非线性屈曲分析,追踪碟形封头发生屈曲失稳前后过程,获取其典型的结构特征。最后将稳定安全系数引入到有限元分析结果的处理中,从而得到可以在工程中应用的许用外压载荷。整个分析方法和结论对碟形封头的设计和校核具有实际的工程意义。     

碟形封头压力容器在内压作用下的弹塑性屈曲及后屈曲行为研究

基于ABAQUS对受内压碟形封头压力容器的弹塑性屈曲及后屈曲行为进行分析.通过非对称网格剖分技术诱发结构的屈曲行为,采用Riks算法捕捉完整的屈曲及后屈曲路径,分析屈曲载荷和后屈曲形态.计算结果表明,在内压作用下碟形封头压力容器过渡区域出现波状的分叉屈曲形态,随着加载的继续,过渡段将逐渐生成肉眼可视的褶皱,进入后屈曲阶段.后屈曲路径可以分为第一阶段与第二阶段.对引入初始厚度缺陷的结果分析可知,初始缺陷厚度的布置将对后屈曲路径产生影响,并降低结构的分叉屈曲载荷.     

碟形封头与筒体连接结构的极限载荷分析

对某内压作用下薄壁容器的碟形封头与筒体连接结构进行了非线性有限元分析,采用了Newton-Raphson算法,得出了最危险点的载荷-位移曲线,进而通过两倍弹性斜率法得到了该结构的极限载荷值。采用正交设计法,研究了封头的壁厚、筒体的壁厚及封头的转角半径对连接结构极限载荷的影响。研究结果表明结构的最大应力位于碟形封头过渡区,对极限载荷的影响由大到小依次为封头壁厚、筒体壁厚以及封头的转角半径,为今后进一步的优化设计提供了依据。     

碟形封头与简体连接处边缘应力的研究

本文在对碟形容器的边缘应力进行理论分析的基础上，开展实验并对实验结果与理论值进行对比分析，探讨了薄膜应力计算公式的正确性，验证了碟形容器的应力计算方法，对容器应力的实际测量有指导意义。     

碟形封头与简体连接处边缘应力的研究

本文在对碟形容器的边缘应力进行理论分析的基础上,开展实验并对实验结果与理论值进行对比分析,探讨了薄膜应力计算公式的正确性,验证了碟形容器的应力计算方法,对容器应力的实际测量有指导意义.     

碟形封头与椭圆形封头形状差的探讨

目前,压力容器在设计上多采用椭圆形封头。随着旋庄设备及技术的引进和发展。旋压封头——碟形封头在压力容器上的应用日益增多。无论是原有设计的修改或新的设计采用旋压技术制造的碟形封头,都要求解决和确定碟形封头参数与其形状的关系及与椭圆封头相比较的形状差、碟形封头与椭圆封头等高的条件,两种封头最大形状差的量值及位置,可能达到的最小形状差及其条件等等一系列问题。     

旋压碟形封头的应用和几何尺寸的选择

1 前言碟形封头采用旋压加工效益明显,目前,国内设计的压力容器多采用椭圆封头,其中以标准椭圆封头(h_i=0.25D_j)最多。根据旋压成形原理,不可能旋压椭圆封头,而实际是旋压碟形封头。碟形封头的推广应用涉及两个方面:一是采用碟形封头代替椭圆封头使用,另一是选定较优的碟形封头几何尺寸参数,并尽快建立旋压碟形封头标准,规定尺寸系列,供设计者直接选用。     

设计与工艺实用数学讲座：第一讲 碟形封头的计算展开

[编者按]本刊约请北京金属结构厂教授级高级工程师孙新铭撰写“设计与工艺实用数学讲座”。作者结合板金结构的设计与加工制造工艺实践，系统介绍机械设计与制造工程中各种常见结构（如椭圆体、椭圆封头、圆柱体、球体、锥体及其相贯等）的数学计算式及其应用。这些计算式大多能够通过计算器和计算机编程运算。应当指出，作者的这些应用数学于生产的经验和体会，虽然主要源自于钣金结构设计与制造，但对其它有关机械工程设计与工艺（如模具、数控加工及常规机械加工等）也能提供数学模型，同样具有实用价值。为了简化讲述，作者将各种机械工…     

啤酒发酵罐用封头形状的分析

近年来,我国新建和扩建的啤酒厂成倍增长。其所用的啤酒发酵罐等主要设备,使用压力一般在０－１ＭＰａ左右,直径为４０００～６０００ｍｍ,大的可达９０００ｍｍ,容积在２００ｍ３以上,属于压力低、直径大的常压或低压容器。对此类容器的设计,在ＧＢ１５０—１９９８的第１章１、３条中明确规定：“不属于该标准的范围”。但目前国内对这类容器的设计,基本都按ＧＢ１５０标准执行,没有针对这类容器的特点,制订相应的行业设计标准。如选用的封头,大都按过去的习惯采用２∶１的标准椭圆形封头。而国外设计的这类容器,如图１所示,…     

Buckling analysis of filament-wound thick composite cylinder under hydrostatic pressure

Underwater vehicles that operate in deep waters require a pressure hull to maintain the sufficient strength and stiffness against external hydrostatic pressure. We investigated the validity of the finite element method (FEM) that is applied to a buckling analysis of the filament-wound composite cylinder, subjected to an external hydrostatic pressure. Two methods were suggested for the buckling analysis of a filament-wound thick composite cylinder under hydrostatic pressure: using the equivalent properties of the composite, and using stacking sequence. The hydrostatic pressure test was conducted to verify the FEA. Test results were compared with the previous results obtained by FEM on the buckling of a filament-wound composite cylinder under hydrostatic pressure. FEM analysis results were in good agreement with the test results. The difference between FEM results and the test results was approximately 1∼5%.     

Experiments on the buckling under internal pressure of thin torispherical ends of cylindrical pressure vessels

Ten cylindrical pressure vessels with torispherical ends, all of the same constant nominal thickness, were tested under internal pressure to observe the buckling behaviour of the toroidal knuckle. All specimens were of constant internal cylinder diameter to thickness ratio of 531·5. The sphere radius was equal to the cylinder diameter and only the torus radius was varied. Buckling was detected by rotating probes at the sphere/torus junction and at the mid-point of the torus. The buckling pressure increased with increasing torus radius and the two specimens with the largest torus radii did not buckle.For all specimens, the change of meridional shape with increase in pressure was measured. For one specimen, strain gauges were used to study the variation of circumferential strain on the inside and outside surface at the sphere/torus junction due to variation in thickness round the circumference.A simple theoretical expression for the buckling pressure, similar to the Rankine formula for a strut, is suggested.     

Search for optimal torispherical end closures under buckling constraints

The optimal geometries of externally-pressurized torispherical end closures, having a prescribed weight, are sought under static stability criteria. End closures are obtained which will withstand maximum or minimum buckling pressures. Their response to initial axisymmetric imperfections is examined and compared to that of hemispherical closures of the same weight and material properties. A direct search technique, known as the complex method of Box (Comput. J.8, 45–52, 1965), is used together with the BOSOR 5 Code as a solver.     

Buckling of T-beams under cyclic bending

This paper presents the results of an experimental study of the response and stability of elastic-plastic T-beams under cyclic pure bending, with emphasis on local buckling. The objectives of the study were to determine the evolution of instabilities and to find parameters useful to determine the degree of damage incurred during cycling. All specimens were subjected to a quasi-static curvature symmetric loading history of constant amplitude. The results indicate that, in the range of curvature amplitudes considered, structural degradation was mainly due to progressive growth of a ripple in the lateral deflection of the web. The unstable growth of one of the features of this ripple led to the formation of a local buckle, which caused a marked reduction in the moment capacity of the specimens. Further cycling resulted in fracture of the web at the local buckle. The best indicator of degradation was a measure of the amplitude of the ripple in the lateral deflection of the web. This measure could be used to generate a criterion for assessing the current state of the specimens in relation to their useful life under cyclic bending.     

Buckling analysis of circular plates of functionally graded materials under uniform radial compression

This study presents the buckling analysis of radially loaded solid circular plate made of functionally graded material. The edge of the plate is either simply supported or clamped and the plate is assumed to be geometrically perfect. The equilibrium and stability equations, derived through variational formulation, are used to determine the prebuckling forces and critical buckling loads. The equations are based on Love–Kirchhoff hypothesis and the Sander's non-linear strain-displacement relation. The results are verified with the known results in the literature.     

Buckling analysis of FGM plates under uniform,linear and non-linear in-plane loading

The paper investigates the buckling responses of functionally graded material (FGM) plate subjected to uniform, linear, and non-linear in-plane loads. New nonlinear in-plane load models are proposed based on trigonometric and exponential function. Non-dimensional critical buckling loads are evaluated using non-polynomial based higher order shear deformation theory. Navier’s method, which assures minimum numerical error, is employed to get an accurate explicit solution. The equilibrium conditions are determined utilizing the principle of virtual displacements and material property are graded in the thickness direction using simple Voigt model or exponential law. The present formulation is accurate and efficient in analyzing the behavior of thin, thick and moderately thick FGM plate for buckling analysis. It is found that with the help of displacement-buckling load curve, critical buckling load can be derived and maximum displacement due to the instability of inplane load can be obtained. Also, the randomness in the values of transverse displacement due to inplane load increases as the extent of uniformity of the load on the plate is disturbed. Furthermore, the parametric varying studies are performed to analyse the effect of span-to-thickness ratio, volume fraction exponent, aspect ratio, the shape parameter for non-uniform inplane load, and non-dimensional load parameter on the non-dimensional deflections, stresses, and critical buckling load for FGM plates.

     

Buckling prevention by lateral fluid pressure in deep-drawing

An instability analysis of flange buckling against lateral fluid pressure in deep drawing is considered. It is intended to explain the experimental fact that relatively low fluid pressure when applied to the flange area can suppress buckling. The analysis is based on the approximate ‘energy method’ with the inclusion of the work against the fluid. The attention is focused on the initiation of the deep drawing process, where buckling (of non-hardening material) is most susceptible. A special apparatus which enables the replacement of a rigid blank-holder by a lateral fluid-pressure was used for testing. A general solution to the critical pressure, above which the deep drawing can be terminated without buckling, is provided. The prediction of the critical pressure and the number of the associated buckling ‘waves’ (wrinkles) agree very well with the experiments. The pertinent geometrical and material variables (as blank thickness, drawing ratio, Young modulus, yield strength, etc.) are grouped in nondimensional form and plotted for various parameters to provide an engineering-type solution for potential users.     

Minimum weight design of beams against failure under uncertain loading by convex analysis

Under operational conditions, some loads acting on a beam are known (deterministic loads), but there usually exist other loads the magnitude and distribution of which are unpredictable (uncertain loads). If the uncertainty in the loading is not taken into account in the design, the likelihood of failure increases. In the present study beams are designed for minimum weight subject to maximum stress and buckling load criteria and under deterministic and uncertain transverse loads. The uncertain load, which is subject to a constraint on its L ₂ norm, is determined to maximize the normal stress using a convex analysis. The location of the maximum stress is determined under the combination of deterministic and worst-case uncertain loads. The minimum weight design is obtained by determining the minimum cross-sectional area subject to stress and buckling load constraints. Results are given for a number of problem parameters including the axial load, elastic foundation modulus and uncertainty levels.