局部减薄储罐拱顶非线性稳定性分析

首先应用非线性有限元法进行局部均匀减薄拱顶的稳定性分析,计算结果表明,罐壁及罐壁油压对罐顶失稳的临界载荷影响很小.随后针对拱顶局部均匀减薄问题,提出一种近似的解析分析法,解析法将减薄部分分离出来,处理为受剩余部分弹性支撑的扁球壳,并导出相应的等效弹性支撑刚度计算公式,最后利用修正迭代法获得近似的失稳临界载荷计算公式.解析方法的计算结果与有限元法计算结果对比表明,文中提出的局部失稳临界载荷计算公式具有与有限元方法相一致的计算精度,可用于局部减薄拱顶储罐的局部稳定性评估,计算结果表明腐蚀区几何参数为9.5时最易出现局部失稳.     

初始挠度及中间弹性支撑对压杆稳定的影响分析

实际工程结构中的细长杆受压时,当存在初始挠度及中间弹性支撑时,不能用经典的欧拉公式计算杆件的屈曲临界载荷.利用有限元软件ANSYS对实际工程结构进行非线性屈曲分析,能够考虑到杆件的初姑挠度以及中间弹性支撑对临界失稳载荷的影响.计算结果表明:机车径向转向架耦合杆初妊挠度为10 mm时,对应的临界失稳载荷相对欧拉公式计算结...     

一种微机电封装中粘接层间剥离应力计算方法

基于弹性力学理论和经典Sujan方法,研究了微机电系统封装中芯片与基板之间粘接层在受到均匀温度载荷时的剥离应力,提出了一种新的计算方法。该方法通过弯矩与曲率的关系,求出曲率方程,进而经由挠度求得剥离应力。经过与Sujan方法和有限元仿真结果比较,显示新的方法能够很好地体现出了剥离应力的变化趋势和在封装结构末端应力集中处的最大剥离应力且新方法与有限元仿真的差值比Sujan方法减小约13%。该方法可为计算封装结构剥离应力提供参考。     

基于有限元法的800MN模锻机工装桁架结构分析

工装桁架为800 MN模锻机安装过程中的辅助结构,在考虑工装桁架C形板安装细节的基础上,应用Ansys软件对工装桁架在C形板安装过程中的力学行为进行有限元分析,计算工装桁架结构在C形板安装过程中的最大应力和最大位移,求出桁架结构的临界失稳载荷,为今后大型设备的辅助安装提供参考。     

内高压成形过程塑性失稳起皱分析

内高压成形过程中,管材的轴向失稳大多发生在塑性阶段,对应的起皱临界载荷是管材进入塑性阶段时的屈服载荷与塑性起皱载荷之和.对于塑性起皱,采用线性硬化材料模型,将本构方程的起算点设置在理想线性强化的起始位置即屈服点,使本构方程有线性形式,建立管材内高压成形起皱临界应力解析表达式.以此为基础讨论力学性能及应力比等对管材内高压成形塑性起皱的影响.结果表明:弹性模量和屈服强度是影响管材抵抗轴向起皱能力的主要力学参数,两者变化参量(决定了管材轴向抗皱能力的变化.当(λ>0时,起皱临界应力绝对值随之增大;当(λ<0时,起皱临界应力绝对值随之减小.应力比对起皱临界应力影响存在两种情况:当最小起皱临界应力对应的起皱失稳发生在颈缩失稳之前,起皱临界应力绝对值随应力比绝对值的增大先减小后增大;当最小起皱临界应力对应的起皱失稳发生于临界颈缩失稳之时,起皱临界应力绝对值随应力比绝对值的增大单调增加.     

45t轻量化门式起重机的优化及局部屈曲研究

针对传统计算方法具有局限性,采用Ansys有限元软件对轻量化门式起重机进行不同工况下静力学分析,得到门式起重机在不同工况下的应力和挠度,从而判断门式起重机是否满足静强度与静刚度的要求。为了得到轻量化目的,将门式起重机主梁腹板和翼缘板变薄,有可能会造成主梁发生局部失稳。通过使用有限元方法对主梁进行线性屈曲和非线性屈曲分析,得到主梁局部失稳的临界载荷和临界应力,为判断主梁是否失稳提供依据,也为解决计算局部稳定性这一难题提供参考和可借鉴的方法。     

基于损伤力学方法的带板连接件疲劳寿命预估

基于损伤力学理论,引入一种分式形式的损伤演化方程,研究飞机带板连接件的疲劳寿命预测方法.根据材料手册中的标准试件疲劳试验数据,确定损伤演化方程中的参数.利用有限元软件Ansys分析得到带板连接件的应力分布.通过几种典型载荷情况下的应力计算,揭示外载荷与钉孔边危险点应力呈线性的特性,从而很方便地根据载荷谱得到危险点应力谱...     

ZJ80/5850DB钻机井架整体结构稳定性分析

以ZJ80/5850DB钻机井架为研究对象,基于弹性稳定理论和有限元方法,对井架整体结构稳定性进行理论计算和有限元仿真分析,再将理论计算和有限元仿真结果进行比较,发现此类型井架临界载荷远大于最大钩载,在实际工作中不会出现失稳问题,可为同类型井架的稳定性分析提供一定的借鉴。     

构型参数对格栅圆柱壳侧压稳定性影响研究

基于有限元参数化建模方法,开展了受侧压格栅圆柱壳的稳定性分析。在总体积相同情况下,以正交格栅、正交各向异性格栅、等格栅圆柱壳为研究对象,分析了圆柱壳包含不同体胞数、不同体胞构型以及给定体胞数时蒙皮厚度、筋骨尺寸变化对结构临界屈曲载荷、失稳模式的影响。计算结果表明:等体积下,格栅圆柱壳存在最佳匹配的体胞构型和体胞数来最大化临界屈曲载荷;侧压圆柱壳最大临界屈曲载荷发生在局部失稳与整体失稳的过渡区。     

弹性复合圆柱滚子轴承接触特性分析

为探讨弹性复合圆柱滚子轴承滚动体与滚道的接触问题,首先采用有限元方法和经典赫兹接触理论计算方法对实心圆柱滚子轴承的接触应力与变形进行计算,并将两种方法得到的计算结果进行比较,比较结果表明:两种计算方法结果误差在10%以内,由此可知,有限元方法对计算轴承接触问题具有准确性。鉴于实心圆柱滚子轴承与弹性复合圆柱滚子轴承的内外圈接触副相似,可采用有限元方法对弹性复合圆柱滚子轴承接触应力分析。通过有限元方法对不同载荷下的弹性复合圆柱滚子轴承的接触应力、接触半宽、接触位移以及接触应力沿轴向分布进行计算与分析,得到的结果表明:一定载荷下,弹性复合圆柱滚动体的接触位移及接触半宽随着填充度的增大而增大;不同载荷下,弹性复合圆柱滚动体接触应力及等效应力随填充度的增大均存在极小值,且随着载荷的增大,极小值呈一定规律变化。弹性复合圆柱滚子轴承较实心圆柱滚子轴承在接触应力方面具有明显优势,设计合理的填充度能降低弹性复合圆柱滚子轴承的接触应力和改善"边缘效应"。     

高温带钢的局部宽度内压屈曲及后屈曲分析

根据工业生产中最主要8种带钢浪形(即板形缺陷)的浪形函数和其对应的带钢纵向不均匀伸长率的横向分布,抽象出产生此浪形的局部内压屈曲过程的位移函数和端边界外力条件,然后分别运用弹性薄板小位移理论和大位移理论建立了屈曲和后屈曲变形模型,并使用能量法进行了求解。在过去对常温态带钢此类问题研究的基础上,对高温态带钢的此类屈曲变形进行理论分析和数值计算,获得了各种工况下的屈曲条件和瓢曲生成路径。     

Long-wave buckling of elastic square honeycombs subject to in-plane biaxial compression

In this study, long-wave and short-wave buckling of elastic square honeycombs subject to in-plane biaxial compression are analyzed using a two-scale theory of the updated Lagrangian type. By taking cell aggregates to be periodic units, the bifurcation and post-bifurcation behavior are analyzed so that the dependence of buckling stress on periodic length can be discussed. It is shown that buckling stress decreases as periodic length increases, and that very-long-wave buckling occurs just after the onset of macroscopic instability if the periodic length is sufficiently long. Then, a simple formula to evaluate the very-long-wave buckling stress under in-plane biaxial compression is derived by exploring the macroscopic instability condition in the light of the two-scale analysis. The resulting formula is verified using an energy method.     

Buckling analysis of laminated composite rectangular plates reinforced by SWCNTs using analytical and finite element methods

In this paper, the buckling analysis of laminated composite plates reinforced by single-walled carbon nanotubes (SWCNTs) is carried out using an analytical approach as well as the finite element method. The developed model is based on the classical laminated plate theory (CLPT) and the third-order shear deformation theory for moderately thick laminated plates. The critical buckling loads for the symmetrical layup are determined for different support edges. The Mori-Tanaka method is employed to calculate the effective elastic modulus of composites having aligned oriented straight nanotubes. The effect of the agglomeration of the randomly oriented straight nanotubes on the critical buckling load is also analyzed. The results of analytical solution are compared and verified with the FEM calculations The critical buckling loads obtained by the finite element and the analytical methods for different layup and boundary conditions are in good agreement with each other. In this article, the effects of the carbon nanotubes (CNTs) orientation angle, the edge conditions, and the aspect ratio on the critical buckling load are also demonstrated using both the analytical and finite element methods.     

An airy function to rapidly predict stresses in wound metal strip having asymmetric thickness profile

With increased demand for thin gage flat metals, control of strip flatness or shape in cold rolling processes has become very important. To improve the flatness quality of cold rolled metal strip and sheet, this work provides a rapid method to predict the transient strains (or stresses) occurring during the rewinding of flat-rolled steels having problematic asymmetric strip thickness profile (or wedge). Flatness control systems, used to monitor and correct the distribution of stress across the width of rolled sheet, are unable to distinguish between stresses induced during rolling, and those caused when rewinding strip containing asymmetric thickness profile. The winding stresses, unless large enough to plastically deform the strip, vanish upon unwinding during subsequent operations such as stamping. Therefore, to help avoid strip flatness defects in thin strip containing wedge, a method is developed to separate the winding stress contribution from the overall stresses that are measured indirectly by flatness control systems. A fourth-order polynomial Airy function is developed to rapidly predict the in-plane stresses based on mandrel wrap number and spatial location on the strip. The Airy function is obtained by applying two-dimensional finite element analysis to study the transient in-plane stresses during rewinding at various numbers of mandrel wraps for a strip containing wedge profile. Three-dimensional finite element analysis is first employed, however, to show justification to a simplified two-dimensional problem described by the plane-stress Airy function. The two-dimensional finite element analysis provides insight as to how the in-plane stresses evolve, and allows determination of coefficients for the Airy function based upon model geometry and displacement boundary conditions. This approach differs from other methods that employ Fourier series to solve the biharmonic equations for an assumed two-dimensional problem. Finally, filtering of the winding stresses from flatness control system input signals is also discussed based on data taken from a rolling mill different to that used for model development.     

Spline finite strip analysis of the buckling and vibration of composite prismatic plate structures

A spline finite strip capability is described for predicting the buckling stresses and natural frequencies of vibration of prismatic plate structures which may be of composite laminated construction with arbitrary lay-ups. The plate structures may have general boundary conditions. The capability embraces analyses based on the use of first-order shear deformation plate theory and of classical plate theory, and utilizes substructuring procedures which include the use of superstrips. The theoretical development is not detailed since the present paper reports a very direct extension of a theoretical study developed for the analysis of single plates in an earlier paper in this Journal. A considerable range of buckling and vibration applications is documented and comparison of spline finite strip numerical values of buckling stresses and frequencies is made with results generated using the semi-analytical finite strip method and, in some cases, the finite element method. Buckled and vibrational mode shapes are presented for some applications.     

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.

     

Coupled approach for flatness prediction in cold rolling of thin strip

The paper presents a predictive model of the flatness defects, which appear during rolling of thin plates, the origin of which is the roll stack thermo-elastic deformation. The combination of the elastic deflection, the thermal crown and the roll grinding crown results in a non-parallel bite, and if the deformed roll transverse profile is not an affinity of the incoming strip profile, differential elongation results and induces high stresses in the outgoing strip. The latter, combined with the imposed strip tension force, result in a net post-bite stress field which may be sufficiently compressive locally to promote buckling. A variety of non-developable shapes may result, generally occurring as waviness (centre waves, wavy edges, quarter-buckles, etc.). This problem is most of the time addressed in a decoupled way, i.e. as a post-processing of the residual stresses computed by a strip rolling model; the present paper on the contrary describes a fully coupled approach of in-bite plastic deformation and post-bite buckling. For this purpose, a simple buckling criterion has been introduced in a FEM model of strip and roll deformation, Lam3/Tec3; its implementation is documented in details. The capabilities and limits of the present approach are described and discussed. Characterised by its coupled approach, it is primarily devoted to cases where on-line (under tension) manifested defects occur. It is shown that the impact of the post-bite, post-buckled stress field on the in-bite stress and strain fields is quite small in the cases investigated; however, subtle changes appear in the velocity field at bite exit, and this is sufficient to transform completely the post-bite stress field, which is found in much better agreement with measurements if such a coupled treatment is used.     

基于粒子群理论的板形模糊模式识别方法

带钢板形的模式识别是板形闭环控制的关键环节,板形模式的识别结果直接影响着板形控制精度.随着板形控制手段的不断更新,对板形模式识别方法提出更高的要求.为克服传统板形模式识别方法抗干扰能力差、逼近阶难以确定的缺点,依据模糊分类原理,运用欧式距离的择近原则对板形模式进行分类,完成板形信号的模式识别.在此基础上,为进一步提高识别精度,将20世纪90年代发展起来的具有全局优化能力的粒子群理论应用于板形模式识别,对模式识别的结果进行优化,并将其与单纯形法优化结果进行对比.试验结果证明了粒子群优化算法的有效性,该算法能够提高识别精度,使优化后的结果能更精确地控制板形调控机构,以适应高精度板形控制要求.     

求解带圆孔的有限宽板的动态应力集中系数的迭加积分法

基于有限元分析,先求出系统在单位脉冲或者单位阶跃的作用下的响应 (即动应力集中系数 ),进而利用离散卷积或Duhamel积分,就可以方便准确地得到系统在同一类型的任意荷载下的响应。对同一构形结构不必对每种荷载都反复进行有限元分析,极大地节省了时间,而且可以得到非常准确的结果。     

壳体屈曲分析中关于能力减弱系数的剖析

工程中通常采用有限元中的线性屈曲方法和非线性屈曲方法来求解壳体的屈曲载荷。对于复杂结构(如钢安全壳),若直接采用非线性屈曲方法求解,除计算工作量大外,还不容易得到符合实际要求的临界载荷。因此,工程中常通过线弹性方法来获得符合实际要求的临界载荷。介绍了壳体屈曲的线弹性理论解,然后利用ANSYS软件求解圆柱壳受轴向和侧向外压的屈曲载荷,并与理论解进行了对比;最后通过对比前人的试验结果与线弹性理论得到的上临界值来剖析"能力减弱系数"的含义和合理性。结果表明:采用线弹性方法来求解壳体屈曲问题是可行的,但必须进一步考虑"能力减弱系数"、"安全系数"和"塑性折减系数"后才能得到工程上所需的临界屈曲载荷值。