偏心拉压杆的载荷动态响应计算

拉压结构杆在结构工程中广泛存在,是重要的承载元件。但因各种误差的存在拉压杆常处于偏心拉压受载状态中,研究其动态响应是保证其正确设计的理论基础。针对等截面直杆承受端部轴向偏心谐和轴向载荷作用时的动态响应问题进行了研究,利用小变形假设和线性叠加原理将问题分解为两个子问题,一个是轴向拉压问题,一个是弯曲问题。给出了细长杆件轴向位移和平面弯曲挠度随不同扰动频率的变化规律,为进一步的动态应力计算奠定了基础,研究思路与应用分离变量法和傅立叶积分变换技术,对于研究杆件承受任意偏心轴向载荷和沿轴向分布荷载的动态响应问题具有重要指导意义。     

伸缩式吊臂在横向、轴向集中力和分布力联合作用下的挠度计算

在轮胎式起重机中伸缩式吊臂是一个重要的工作部件。工作时,吊臂的挠曲变形过大将会严重影响起重机的工作性能。因此,在臂架设计时,需计算吊臂的挠度,使其小于一定的许用值,以满足刚度的要求。另外,当存在轴向分布力和集中力时,轴向分布力和集中力对截面产生的弯矩与吊臂的挠曲变形有关。因此,要进行结构的强度计算也要求先求出吊臂的挠度。     

计及二阶效应的一种桁架臂几何非线性方法

基于二阶效应,运用微分方程法建立承受横向均布载荷压杆在变形位置后的微分方程,将微分方程分解为均承受轴向压力的正弦曲线和二次抛物线曲线的叠加,把变形方程变换成以待定几何参数表达的形式,根据边界条件和平衡条件求解承受横向均布载荷的压杆挠度计算公式;采用该方法对等截面空间桁架臂进行挠度变形分析,并将所求结果与有限元软件ANSYS和ABAQUS非线性分析结果进行对比分析,对比结果验证了所提出方法的可行性与实用性。     

卧式液压缸挠曲特性研究

为了研究卧式液压缸挠曲特性,提出了一种卧式液压缸挠度计算方法和改进液压缸挠曲形态的优化方案.基于阶梯杆模型,考虑活塞杆吊耳与液压缸缸体铰支点轴承摩擦,活塞杆与导套、活塞与液压缸内壁的配合间隙,液压缸截面特性及缸尾弹簧支撑,建立了卧式液压缸的挠曲力学模型.将轴向载荷对挠度的影响转换为轴向载荷影响系数,提出了计算卧式液压缸挠度的二截面受压杆法.以三峡新通道船闸人字闸门液压启闭机液压缸比例物理模型为实例,进行了有限元仿真与试验,验证了二截面受压杆法.结果 表明:二截面受压杆法相比试验均方根误差小于0.616 mm;由于两铰点处轴承摩擦的影响,液压缸挠度减小2.8％～9.7％;增设弹簧支撑后,液压缸挠曲形态明显改善,缸尾挠度减小36.1％～61.2％、活塞杆挠度减小41.2％～61.3％.在额定载荷内,自重挠度占比不低于70％,自重是影响液压缸挠度的主要因素.     

双安全钳作用下的电梯导轨建模与变形分析

结合双安全钳作用特点,以多跨度细长杆模型为基础,建立并求解了电梯导轨在复杂受力状态下的弯矩方程和挠曲线方程。计算对比了双安全钳和单安全钳作用对导轨弯曲变形与临界力的影响,最后通过试验验证了建模的正确性。研究结果表明双安全钳可以有效降低导轨的最大变形和最大应力,提升电梯安全性。     

柔性机械系统动力学的变形耦合方法

采用弹性广义坐标耦合形式描述柔性构件的变形场 ,引入非线性位移 -应变关系确定新的形函数 ,使柔性体广义变形坐标 -应变成为线性关系 ,采用这种线性形式描述柔性体的应变能。将含变形广义坐标二阶项保留到求出偏 (角 )速度后再线性化 ,根据Kane方程建立了基于小变形的柔性机械系统动力学一致线性化模型。对含柔性梁的急回机构动力学进行了仿真研究。仿真结果表明曲柄在一些特定转速下 ,柔性梁出现失稳 ;在某些转速时 ,柔性梁动响应具有拍频特征。     

微细铣刀螺旋沟槽包络计算与微量补偿刃磨研究

微细刀具的制造方法是保证微细铣刀制造精度的技术关键。从砂轮与工件的相对运动关系出发,依据砂轮与工件的啮合条件,分析砂轮表面法矢量在母线交点处的变化情况,建立砂轮与螺旋沟槽完整公共接触线方程,由接触线围绕工件轴线回转形成回转面的轴向截形,推导出铣刀轴向截形的廓形方程,同时根据廓形方程仿真出沟槽截形,据此分析了安装参数对截形的误差敏感度。在刃磨微细铣刀螺旋沟槽过程时,提出采用Z轴插补对挠曲进行补偿的方法,通过计算刃磨过程的挠曲变形量,相应地在工件的轴向位置补偿变形量。实验表明,补偿后实得微细铣刀的前角和芯厚与仿真的铣刀螺旋槽几何参数吻合良好。     

基于Matlab PDE Tool Box的构件特征值问题分析

利用Matlab提供的偏微分方程工具箱(PDE Tool Box),对两端铰支细长压杆失稳以及横向自由振动平板的特征值的求解过程进行了阐述,分析了细长压杆失稳的临界力和横向振动各阶固有频率以及横向自由振动平板的各阶固有频率.结果证明该方法操作简单,速度快,误差小.     

基于Matlab PDE Tool Box的构件特征值问题分析

利用Matlab提供的偏微分方程工具箱（PDE Tool Box）,对两端铰支细长压杆失稳以及横向自由振动平板的特征值的求解过程进行了阐述,分析了细长压杆失稳的临界力和横向振动各阶固有频率以及横向自由振动平板的各阶固有频率。结果证明该方法操作简单,速度快,误差小。     

铝合金E形截面构件受弯整体屈曲临界弯矩确定方法

针对在门窗和幕墙工程中广泛使用的铝合金E形薄壁截面构件,文中通过分析不同长细比构件在受弯整体屈曲时挠度-弯矩曲线、轴向应变-弯矩曲线的特征和联系,探讨了在挠度-弯矩曲线无极值时,铝合金E形截面构件受弯整体屈曲临界弯矩的确定方法。     

Hydroforming of aluminum extrusion tubes for automotive applications. Part I: buckling, wrinkling and bursting analyses of aluminum tubes

Three possible failure modes have been identified in tube hydroforming: buckling, wrinkling and bursting. A general theoretical framework is proposed for analyzing these failure modes as an elastoplastic bifurcation problem. This framework enables advanced yield criteria and various strain-hardening laws to be readily incorporated into the analysis. The effect of plastic deformation on the geometric instability in tube hydroforming, such as global buckling, axisymmetric wrinkling and asymmetric wrinkling, is precisely treated by using the exact plane stress moduli tensor. A mathematical formulation for predicting the localized condition for bursting failure is established herein. Furthermore, the critical conditions governing the onset of buckling, axisymmetric wrinkling and asymmetric wrinkling are derived in closed-form expressions for the critical axial compressive stresses. Closed-form solutions for the critical stress are developed based on Neale–Hutchinson's constitutive equation and an assumed deformation theory of plasticity. It is demonstrated that the onset of asymmetric wrinkling always requires a higher critical axial compressive stress than the axisymmetric one under the context of tube hydroforming with applied internal pressure and hence the asymmetric wrinkling mode can be excluded in the analysis of tube hydroforming. Parametric studies show that buckling and axisymmetric wrinkling are strongly dependent on geometric parameters such as t₀/r₀ and r₀/ℓ₀, and that axisymmetric wrinkling is the predominant mode for short tubes while global buckling occurs for long slender tubes.     

Comparative study of thermal post-buckling analysis of uniform slender & shear flexible columns using rigorous finite element and intuitive formulations

Thermal post-buckling analysis of uniform, isotropic, slender and shear flexible columns is presented using a rigorous finite element formulation and a much simpler intuitive formulation. The ends of the columns are axially restrained to move and consequently any temperature rise above the stress free condition of the column produces an equivalent constant compressive mechanical load that causes the column to buckle at a critical temperature. Further increase in temperature beyond critical temperature results in the thermal post-buckling phenomenon. As a result of constraints imposed on the axial displacement at the ends of the column, the post-buckling phenomenon is governed by the von-Karman strain displacement relation applicable to one dimensional problems. Empirical formula for ratio of nonlinear axial load to critical load (equivalent constant mechanical load for a given temperature rise) as a function of the central deflection are obtained using both the rigorous finite element and intuitive formulations for various boundary conditions. The boundary conditions considered are the classical such as hinged-hinged, clamped-clamped and clamped-hinged conditions and nonclassical boundary conditions like the hinged-guided or the clamped-guided conditions. Post-buckling analysis results pertaining to nonclassical boundary conditions are meagre in the literature. It is observed that results obtained from both the formulations are in excellent agreement for all boundary conditions considered. Also the accuracy and simplicity of the intuitive formulation is aptly demonstrated to slender and shear flexible columns.     

A theoretical determination of the contact pressure across the central meridian of a belted radial tire

A belted tire is supposed to be loaded at its hub and pressed into contact with a flat frictionless roadway. The contribution to the contact pressure due to the flexibility of a meridional section is determined for the section containing the plane of symmetry of the circumference. This section is modeled as a beam of unit depth subjected to a distributed load due to tread compression and circumferential deformation. The beam is supported at its ends by shear forces and moments applied by the side walls of the tire. A solution of the differential equation governing the additional transverse deflection due to meridional bending is obtained by a singular perturbation procedure. The contact pressure associated with this solution increases rapidly in boundary layers at either edge of the beam. The maximum value of this pressure is about ten percent of the uniform contact pressure determined in a circumferential analysis supposing the meridian to be rigid.     

Buckling of shallow spherical shells including the effects of transverse shear deformation

The large deflection equation of a shallow spherical shell under uniformly distributed transverse loads is established in this paper with consideration of effects of transverse shear deformation on flexural deformation. Using an updated iteration method, an analytical solution for nonlinear stability of a shallow spherical shell is obtained. Formulae for estimating the critical buckling loads are presented for two types of boundary conditions. Discussions on the influences of the geometric and physical parameters on the critical buckling loads are given.     

The failure of torispherical ends of pressure vessels due to instability and plastic deformation—An experimental investigation

Twelve model pressure vessels with torispherical ends have been tested under internal pressure to investigate failure by instability and plastic deformation. The models covered combinations of three head heights and four thicknesses. All the thicker specimens with internal diameter-thickness ratios of 53, 106 and 212 failed by plastic deformation. The three thin specimens with an internal diameter-thickness ratio of 530 failed by buckling of the torus due to the circumferential compressive stresses. The experimental results for limit pressure and instability failure are compared with theoretical values. The effect of change of geometry is significant particularly for the larger head heights. For these specimens the experimental limit pressure is higher relative to theoretical predictions than is the case for the smaller head heights. A simple approximate theory is presented for predicting the pressure at which buckling occurs in the torus. The correlation of the new predictions with the experimental values is not good, but the new predictions are lower than those previously published.     

Nonconservative dynamic axial–torsional buckling of structural frames using power series

Axial deformation is not involved in the formulation of linear buckling caused by axial force. Likewise, twisting is not present in linear buckling caused by axial torque. The dynamic axial–torsional buckling of structural frames in the presence of follower axial force will be solved by means of dynamic stiffness using power series. Variationally consistent natural boundary conditions are given so that the resulting dynamic stiffness is symmetrical for conservative loading. Some parts of the boundary forces disappeared for follower axial forces due to consistent tangency to the neutral axis. The deficiency of the power series method to deal with non-uniform sections is highlighted. New instability phenomena for a simple column are studied in detail. It is shown that columns can buckle under direct follower tension. Follower tension decreases the natural frequency initially and then increases it rapidly after a turning point. The first pair of modes about the major axis and that about the minor axis of a rectangular section column meet at one crossing point. A very small axial torque will change the crossing into flutter-like tongues. These tongues are common in compressive follower force. These tongues caused by axial torque are reported here for the first time.     

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...     

Large deflection analysis of a thin walled channel section cantilever beam

For a special application the large deflection behaviour of thin walled channel section beams made of thin sheet steel has been investigated. The experiments consisted of cantilever bending tests with the beam loaded through the shear centre and through the centroid. When loaded through the shear centre the beam buckling took place in the compression flange at the root of the cantilever. When loaded through the centroid however, it was noted that the compression flange buckled at a fixed distance from the fixed end. The general theory of thin walled beams developed by Vlasov was applied to the problem and indicated that the maximum compression stress at the edge of the flange would be at some distance from the fixed end. The value of the maximum compression stress obtained by the general linear theory was small and its position did not coincide with the experimental position. The Vlasov analysis has been modified to include the increase in the twisting moment due to the lateral deformation of the beam along its length. Good agreement between the modified theory and experiment both for the position of the maximum compressive stress and for the twist of the cantilever at three points along its length.

Because of the very low torsional stiffness of thin walled channel sections, the small deflection theory is only applicable for small bending loads applied through the centroid and the modified theory should be used for practical loading cases.     

Influence of pre-buckling displacements on the elastic critical loads of thin walled bars of open cross section

Nonlinear expressions for the strains occurring in thin walled bars of open cross section, when subjected to axial, flexural and torsional displacements, are incorporated in a general instability analysis based on the vanishing of the second variation of the total potential energy. It is shown that the influence of the pre-buckling displacements is automatically included in the analysis. A closed form solution for the lateral buckling of a simply supported beam subjected to uniform bending agrees exactly with a solution based on the governing differential equations. Solutions obtained using numerical methods are also presented. The significance of the second order axial strains induced by rotation about the shear centre, is investigated by considering the instability of an inverted T-beam subjected to uniform bending.     

卧式水电机组用径向滑动轴承热弹流特性分析

研究轴颈挠度和瓦块表面热弹变形对卧式水电机组径向滑动轴承静态润滑性能的影响。推导考虑轴颈挠度和轴瓦热弹变形后的油膜厚度表达式;用中心差分法结合ANSYS软件联立求解雷诺方程、能量方程、固体热传导方程、密度方程、黏度方程和轴瓦热弹变形等,得到径向滑动轴承的热弹流润滑(TEHD)特性,并与不计入轴颈挠度及轴瓦热弹变形的油膜动压润滑特性进行比较。结果表明:在考虑轴颈挠度和轴瓦瓦面热弹变形的影响后,油膜压力、温度、厚度沿着轴承宽度中心线的对称特性消失;油膜压力峰值增大,峰值点位置由轴向中心区偏移至出口区;油膜温度峰值增大,最高温度发生在出口区;润滑区内的最小油膜厚度大幅度减小,油膜最小厚度处于出口侧边界附近;轴承润滑流量减小,损耗略有增大;轴承稳态运行时,轴颈偏位角基本一致。