循环热-机械双轴载荷下薄壁圆筒的热棘轮极限

热棘轮失效是薄壁圆筒的主要失效模式之一,现有ASME锅炉及压力容器规范和EN13445等设计标准主要考虑环向应力,而未考虑轴向应力条件,使得设计结果可能偏于不安全。针对循环热-机械双轴载荷下薄壁圆筒热棘轮设计理论的不足,采用非循环分析方法系统研究双轴应力状态下薄壁圆筒热棘轮极限的解析解,重点考虑轴向压缩应力对循环温度梯度和稳定内压组合载荷下薄壁圆筒热棘轮极限的影响,并提出相应的设计方法,并采用有限元法对理论结果进行验证。结果表明,循环热-机械载荷下轴向压缩应力会显著降低薄壁圆筒的热棘轮极限,且理论解与有限元分析结果吻合良好,这说明此方法可用于循环热-机械双轴载荷及类似工况下薄壁圆筒的热棘轮设计限,具有良好的工程价值。     

超高压管式反应器端部结构应力场的数值模拟

基于大型通用有限元软件ANSYS,对发生疲劳断裂的超高压管式反应器的端部结构进行数值模拟,分析了其在过盈套合、自增强处理以及服役期间开停工循环载荷三种工况下的局部应力场.结果表明:三种工况下,端部结构在过盈套合边缘局部范围内均存在较高的轴向拉应力,且大于环向应力;局部轴向应力随套合过盈量和自增强压力的增加而增大;半径过盈量为0.05 mm时,开停工循环载荷下的局部轴向平均应力最大值可达86.71 MPa,轴向交变应力幅值最大值达到62.2 MPa,裂纹垂直于轴向扩展的推动力较大.模拟分析结果对端部结构失效破坏原因的分析及其设计改进有一定的指导意义.     

Optimally reinforced cutouts in laminated circular cylindrical shells

The problem of designing a cutout in a load bearing structural member in the form of a shell, such that the cut structure maintains its stress state with a minimal departure from the stress state of the uncut structure is addressed herein. Symmetrically laminated composite circular cylindrical shells under hydrostatic compression and axial pressure are considered. Shallow thin shell (Donnell shell theory) lamination theory is utilized. The original (uncut) stiffness of the shell structures is recovered considerably by appropriately designing an edge reinforcement around the cutout. The buckling load of the designed shells are analyzed via the finite element method. An experimental investigation has been carried out to verify some of the results obtained from the finite element analysis. In the work presented, the reinforcement is modeled as a one-dimensional rod/beam type structural element.     

深沟球轴承的载荷分布与刚度特征研究

采用有限元法计算了"奇压"与"偶压"两种受载形式下深沟球轴承的静力学响应。对比讨论了轴承内接触应力分布、轴承变形及刚度的变化特征。结果表明当外载荷达到某一值时,关键滚动体与外圈滚道接触中心的接触应力明显大于与内圈滚道接触中心的接触应力,并随着载荷的增加,这个趋势越发明显;两种受载形式下,轴承的位移与刚度表现出明显的差异,奇压形式下,轴承的径向位移小于偶压形式下的径向位移,而奇压形式下的轴承刚度则大于偶压形式下的刚度;相同载荷作用下,静力学方法计算的轴承径向位移小于有限元法计算结果。     

Elastic lateral-torsional buckling of circular arches subjected to a central concentrated load

An arch under an in-plane central concentrated radial load is subjected to combined axial compressive and bending actions. When these combined axial compressive and bending actions reach a certain value, the arch may suddenly deflect laterally and twist out of its plane of loading and fail in a lateral-torsional buckling mode. This paper derives analytical solutions for the elastic lateral-torsional buckling load of pin-ended circular arches that are subjected to a central concentrated load, using the principle of stationary potential energy in conjunction with the Rayleigh-Ritz method. Analytical solutions of the buckling load for in-plane fixed and out-of-plane pin-ended arches and for the case of the load acting above or below the shear centre are also derived. The analytical solutions are compared with results of a commercial finite element package ANSYS and a finite element code developed by authors elsewhere for arches with different slendernesses, included angles, and cross-sections. The agreement between the analytical solutions and the finite element results is very good.     

Influence of hardening rule on prediction of cyclic plasticity in pressurized thin tubes subjected to cyclic push-pull

The paper considers the cyclic plastic behaviour of a thin-walled tube subjected to steady internal pressure and cyclic reversed axial push-pull. Tubes under such a loading combination are known to exhibit continued strain growth in the hoop direction. The steady-state behaviour of the tube is investigated using a number of hardening rules within the framework of time-independent plasticity theory. Isotropic hardening and Prager kinematic hardening are considered first and shown to yield no strain growth at the steady state. When a kinematically hardened yield surface is assumed to translate in the direction of the stress rate vector, considerable steady-state strain growth is predicted in the hoop direction. Consideration of two-surface plasticity theory yields also large steady-state strain growth. Closed-form analytical expressions are derived for growth rates and ranges of cyclic plasticity for all hardening rules considered. Contours of strain growth are plotted for practical ranges of primary and secondary stresses using representative material properties. Comparison with limited test data indicate that the predicted steady growth rate is larger than about four times observed rate.     

扭曲管换热器管板的有限元分析

采用有限元分析软件ANSYS,对扭曲管换热器的管板在三种工况下的应力进行计算,分析了扭曲管轴向刚度削弱系数对管板应力强度及扭曲管轴向应力的影响。结果表明,扭曲管的轴向变形补偿能力优于普通直管,可以降低在温差载荷作用下管板中的应力,但会提高压力作用下的管板应力。在压力载荷作用下,扭曲管上的平均应力大小与普通直管差别不大,但扭曲管的轴向应力在管子横截面上的分布不均匀,局部的轴向应力远远高于平均应力水平,因此扭曲管抗疲劳和应力腐蚀开裂的能力不如直管。不同厚度的管板受扭曲管管束轴向刚度的影响不同,当管板厚度较小时,扭曲管管束轴向刚度的影响较大。     

甲醇合成塔管板结构改进设计

甲醇合成塔管板结构设计是合成塔设计的关键。对某甲醇合成塔管板采用挠性过渡圆角结构,进行改进设计,以增加管板的挠性,同时应用有限元法对管板应力强度和换热管轴向稳定性进行分析。结果表明改进设计的管板过渡圆角处应力强度大大降低,换热管轴向压应力有所减小,提高了其抗压稳定性。研究结果为高温高压换热器管板结构优化设计提供了依据。     

Identifying axial load patterns using space frame FEMs and measured vibration data

The axial loading of a space frame may need to be quantified, perhaps for improvement of a finite element model (FEM) to better represent the structural dynamics or to ascertain how close the structure is to buckling. The coexistence of compressive and tensile forces in a space frame causes certain frequencies to increase with respect to load while others decrease. This intricate behaviour has been modelled in the FEM of a bi-tetrahedral space frame through consideration of the geometric stiffness, which accounts for stiffness changes in the loaded members. Updating the load pattern in the FEM using Newton's method (traditional sensitivity-based model updating) brings the model frequencies closer to those physically measured from the real bi-tetrahedral frame and thus provides identification of the axial loads. This load pattern is a predetermined set of frame axial forces in equilibrium. Such a constraint means that the extent of loading can be described by just one scalar updating parameter, an improvement upon former methods that updated member forces as independent parameters. When compared to the loads measured using strain gauges, the loads identified by model updating are seen to offer approximations of the actual loading. Difficulties such as modelling joint behaviour are discussed. The present work extends a series of numerical studies on load updating published by the authors by offering a demonstration of load pattern identification using physically measured vibration data from a real space frame.     

Effect of intervertebral disc degeneration on biomechanical behaviors of a lumbar motion segment under physiological loading conditions

The consideration of biomechanical alterations due to intervertebral disc (IVD) degeneration is crucial for the accurate analysis of spine biomechanics. In this study, finite element (FE) models of the L4-L5 motion segment with full coverage of the degeneration grades from healthy IVD to severe degeneration were developed. The effects of IVD degeneration on spine biomechanics were analyzed under physiological loading conditions using compressive forces and bending moments. The FE models of all degeneration grades were consistent with published data in terms of the ranges of motion. Severe IVD degeneration showed lower inter-segmental rotations in flexion-extension and lateral bending, lower intradiscal pressure in all motions, higher facet joint forces in lateral bending and axial rotation, and higher von-Mises stress in annulus ground substance in all motions versus the healthy IVD. These findings could provide fundamental information for understanding the characteristics of the biomechanical behaviors of degenerated lumbar motion segments.     

Autofrettage of thick-walled pipe bends

The bending of a thick-walled cylinder to a given radius involves an elastic–plastic deformation that results in a residual, axial stress distribution. The latter alternates from maximum tension to maximum compression between top and bottom halves of the cross-section. The residual stress levels depend upon the depth of plastic penetration and may be determined as a closed solution when they arise from a bending moment applied to either a non-hardening or linearly-hardening material. When the bent pipe receives an autofrettage treatment without an intermediate heat treatment, this produces a further residual, triaxial stress state. The interaction between the residual states from bending and autofrettage has an important effect upon the net axial stress and the equivalent stress. It is shown that large plastic penetrations arising from bending and autofrettage can residually stress the section beyond its yield point: in tension and in compression across both its halves. With the unloading from each process, a Bauschinger effect reduces the yield point to assist with the onset of reversed plasticity. The latter is far less beneficial than when unloading is elastic. It is shown how a nonlinear kinematic hardening model can be employed to avoid unloading plasticity at the inner and outer diameters. The consequence of interacting residual stresses is that axial stress can play as important a role as hoop stress when designing for safe service loadings. In general, an enhanced residual stress state is beneficial when compressive but detrimental when tensile. Pre-compression is often employed in practice to reduce tensile stress arising from internal pressure, axial force and self-weight. Here, the compressive residuals arising from an autofrettage treatment have long been exploited to enhance the fatigue life of process piping and weaponry.     

膨胀管实体膨胀锥受力分析与膨胀试验验证

膨胀管技术主要应用在油气田开发领域,膨胀锥是膨胀管技术主要工具之一,在工作时受到极大的界面应力,因此膨胀锥表面过快磨损是制约膨胀管技术发展的主要问题之一。为探究膨胀过程中膨胀锥体表面受力和应力分布,结合弹塑性理论推导膨胀锥接触应力和摩擦力计算模型,采用有限元方法模拟膨胀管膨胀过程,研究膨胀锥表面应力、接触摩擦应力和膨胀推力变化情况,并通过膨胀试验验证了有限元模拟结果的合理性。结果表明：影响膨胀锥接触应力和摩擦力的主要因素是膨胀管屈服强度和膨胀锥锥角;膨胀锥的最大等效应力集中在大径圆角处,最大摩擦应力集中在膨胀锥小径和大径处;膨胀锥膨胀区只有部分与膨胀管内壁接触,膨胀锥小径处受拉应力,大径处受压应力,最大接触压应力集中在大径处。     

Approximation method for the calculation of stress intensity factors for the semi-elliptical surface flaws on thin-walled cylinder

A simple approximation method for the stress intensity factor at the tip of the axial semi-elliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks witht/R=0.1. The approximation solutions are within ±2.5% of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1–3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.     

厚壁圆筒自增强压力的优化分析

采用考虑材料应变强化效应和包辛格效应的双线性材料模型,建立了厚壁圆筒自增强理论模型。基于工作时的等效应力及周向应力,提出了最佳自增强压力的评定方法并给出了理论求解过程。采用有限元软件对自增强厚壁圆筒涉及的三个加载过程进行模拟分析,模拟结果与理论计算结果相吻合。由模拟结果得到了厚壁圆筒工作时的最大等效应力和最大周向应力与自增强压力的关系曲线,并采用直接加权组合法进行优化,得到了最佳自增强压力。研究结果为厚壁圆筒最佳自增强压力的求解提供了新思路,具有一定的工程意义。     

Stiffness Analysis of Corrugated Flexure Beam Used in Compliant Mechanisms

Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam(CF beam) is designed because of its large flex...     

A study of a finite element model for the chemical mechanical polishing process

In this paper, relative velocity at a given point on the wafer was first derived. The revolutions of wafer and pad are assumed the same and the axisymmetric uniformly distributed pressure form is given. Thus, a 2D axisymmetric quasic-static model for chemical-mechanical polishing process (CMP) was established. Based on the principle of minimum total potential energy and axisymmetric elastic stress-strain relations, a 2D axisymmetric quasic-static finite element model for CMP was thus established. In this model, the four-layer structures including wafer carrier, carrier film, wafer and pad are involved. The von Mises stress distributions on the wafer surface were analysed, the effects of axial, hoop, radial and shear stresses to von Mises stress and the effects of axial, hoop, radial and shear strains to deformation of the wafer were investigated. The findings indicate that near the wafer centre, von Mises stress distribution on the wafer surface was almost uniform, then increased gradually with a small amount. However, near the wafer edge, it would decrease in a large range. Finally, it would increase dramatically and peak significantly at the edge. Besides, the axial stress and strain are the dominant factors to the von Mises stress distributions on the wafer surface and the wafer deformation, respectively.     

Application d'un modèle de flambement conditionné à la pose des câbles à fibres optiques

Application of a conditioned buckling solution to the laying of optical cables. Mechanical behaviour of cables submitted to an axial compressive load is subjected to buckling instabilities due to their length compared with their diameter. In some cases rigid walls modify the boundary conditions during the loading or the buckling phenomenon, it will be called conditioned buckling. This paper presents the buckling of a homogeneous cable in a horizontal circular rigid duct subjected to its own weight and an axial compressive load. Buckling load and pitch associated to sinusoidal and helical buckling are determined as transmission of axial load during buckling. A finite element simulation is computed and comparisons are made with the analytical solution. A direct application to the optical fibre cable laying in underground duct is made and experimentation is conducted with a life-sized bench designed at the LM ² S of the ENSAM of Paris and located at the CNET Lannion. Comparisons between experimental and analytical results are presented.     

基于EDEM的井下挖掘装载一体机主车体设计研究

设计一种轮履结合的可变履带式井下挖掘装载一体机,既发挥了轮式一体机转弯灵活,转弯半径小和履带式一体机越野机动性强,运行稳定的优势,又克服了轮式一体机越障、爬坡能力弱和履带式一体机转弯差的缺陷。该文利用EDEM软件对动态散状煤物料进行量化分析,得到了装载过程中,煤物料与井下挖掘装载一体机主车体碰撞的接触应力集中部位,接触速度矢量变化方向和煤物料运动趋势,最大接触法向力与切向力出现的时间与数值,进而对主车体结构改进方向和有限元静态分析主车体刚度起到了一定的指导和借鉴作用,为今后井下挖掘装载一体机其他部件的优化设计及动态参数的获得提供参考。     

The effect of axial loading and axial restraint on the thermal ratchetting of thin tubes

The finite element method has been used to investigate the thermal ratchetting behaviour of thin tubes subjected to steady, internal pressure and cyclic, linear, through-thickness temperature distributions. An elastic-perfectly plastic material behaviour model was used and uniaxial behaviour was related to multiaxial behaviour via the von Mises yield criterion and the Prandtl-Reuss flow rule. Results for a tube without axial stress, a tube with axial stress (corresponding to a tube with an end closure) and a tube constrained to have no axial strain, are presented. Correlations with a simplified analytical solution were attempted. Good correlations were obtained for the tubes without axial restraint. The correlation for the axially constrained tube was poor because the thermal loading is essentially different. In the case of the axially constrained tube, if the thermal load is high enough, yielding occurs through the whole of the wall thickness simultaneously in each half cycle. This is not possible in the other two cases considered.     

一种考虑胶瘤的胶接简化有限元模型:应力与刚度分析

胶接接头中总存在胶瘤,由于建模复杂,胶接接头有限元分析中胶瘤常被忽略.但胶瘤能减少峰值应力,提高结构强度和刚度.为此,提出一种简化的胶接有限元模型,即用壳单元代表胶瘤,体单元代表被粘体和胶层,并用弹性理论建立壳单元等效厚度公式.以体单元精细模型结果作为对比的真实解,考察五种载荷工况下,单搭接头简化有限元模型的胶层应力和刚度.分析表明,壳单元等效厚度公式正确,胶接简化有限元模型精度高,可用于诸如汽车等大型结构中;用壳单元简单模型可定量分析胶瘤大小和形状对接头应力和总体刚度性能的影响.