Thixotropy of greases and low-speed operation of rotational plastoviscometers and rolling bearings

Summary A typical property of greases, as plastic disperse systems, is their thixotropy (reversible destruction of their structure due to deformation). In relation to this, if the rate of their formation drops below a certain critical value it becomes practically very difficult or even impossible to attain steady conditions of their flow. This is observed both in rotational plastoviscometers and in rolling-contact bearings, and is manifested in more or less sharp fluctuations of the resistance moments. The critical value of the rate of deformation depends on the nature of the grease and the rigidity of the braking device or the power reserve of the drive, decreasing when these values are increased. When soap greases are deformed they become anisotropic, which, when the direction of deformation is changed, tells perceptibly on their resistance to deformation and results in fluctuations of the resistance moments in rolling bearings.     

Plastic collapse of general frames

A structural theory is presented for the large static plastic deformation of space frames composed of thin walled members. Displacements comparable to the overall structural dimensions are contemplated. The frame is considered to consist of an arbitrary number of beam elements connected at node points. The analysis assumes that plastic deformation is confined to idealized hinges located at the node points. As a basis for a general frame computer program, the equations for a beam element are derived as a relationship between appropriate generalized force and deformation rates. The structural constitutive theory employed for the plastic hinge includes biaxial bending, torsion, and axial extension. It accounts for reduction in the load carrying capacity of the hinge due to local deformation. Predicted force-deformation curves for a space frame are in good agreement with experimental results.     

大范围运动细长柔性空间结构动力学特性分析

自由-自由边界无约束状态的细长柔性空间结构大范围运动时的动力学特性对整体结构运动分析和运动控制系统设计具有极其重要的作用。通过浮动坐标系建立结构的运动学关系;借助假设模态法对结构变形进行变量分离;利用Lagrange’s方程建立了结构的刚柔耦合振动方程;再通过Rayleigh-Ritz法,以无大范围运动时的振型函数作为基本解组,得到了大范围运动影响下的结构振动特征方程,求解该方程得到了结构频率和振型。通过几组数值算例的对比分析,指出了非耦合模型和耦合模型下结构频率及振型之间的差异。     

航空薄壁弧形结构件喷丸强化变形预测

喷丸强化是一种有效提高工件抗疲劳性能的表面处理工艺，经喷丸强化处理后的航空薄壁弧形结构件发生变形是航空制造领域的共性难题．本文基于变截面曲梁平面弯曲理论，建立了弧形件喷丸诱导应力与变形方程，将得到的构件最大变形与有限元方法计算结果进行对比，所建立理论模型能有效预测弧形件喷丸强化后的变形．讨论了喷丸压力和喷丸区域对喷丸变形的影响，结果表明：喷丸强化工艺仅作用于弧形件腹板表面时，弧形件变形以径向收缩为主；喷丸强化工艺仅作用于弧形件筋板表面时，弧形件变形以径向扩张为主；与局部喷丸相比，对弧形件所有表面喷丸强化时，弧形件弯曲变形减小，轴向伸长增大．     

Mechanical properties of isolation bearings identified by a viscoelastic model

The Haringx theory is usually employed to describe the mechanical behavior of rubber bearings subjected to a compressive axial load and a lateral shear deformation, but it does not consider the damping effect. In order to study the behavior of isolation bearings which possess an energy-dissipation capacity, the explicit formulas for the horizontal stiffness of viscoelastic columns and the corresponded height reduction are derived by the method of variable separation. These explicit formulas are then applied to develop an identification procedure to find the shear modulus and loss factor of the rubber using the cyclic shear tests of isolation bearings. Through this identification procedure, the empirical formulas for the shear modulus and the loss factor of rubber are established as functions of the strain amplitude and the excitation frequency.     

Slope-deflection method for elastic-plastic multistory frames

Slope-Deflection Method for elastic rigid frames is generalized for elastic-plastic analysis of rigid frames of work-hardening materials. The plastic strain is here treated as an additional set of externally applied moments. The end moments of the component members of the frame are obtained from the solution of a set of linear algebraic equations. No iteration is required. Numerical results of the analysis of a portal frame and a two-story plane frame subject to side loads beyond the elastic range are shown.     

计及机体变形的内燃机主轴承弹性流体动力润滑分析

针对某四行程四缸内燃机曲轴主轴承,考虑机体变形因素的影响,进行了曲轴轴承弹性流体动力润滑分析.计算中采用动力学法进行曲轴轴承的润滑分析,采用变形矩阵法计算油膜压力作用下轴承表面的变形.结果表明,与不考虑机体变形影响相比,计入机体变形影响时轴承轴心轨迹基本没有改变,在1个工作循环中的大部分时间轴承最大油膜压力、最小油膜厚度、端泄流量和轴颈摩擦系数几乎没有变化,仅在某些时刻附近轴承最大油膜压力略有减少,轴承最小油膜厚度略有增加.因此在计算精度要求不是非常高的情况下,曲轴主轴承润滑分析可以不考虑轴承表面因油膜压力作用产生的弹性变形的影响.     

基于GPS伪距单差的舰船相对导航方法

为了测量编队航行中的舰船相对位置信息,从而进行相对导航,研究采用GPS卫星的伪距信息,通过编队通信链,交换目标船和跟踪船的观测到相同卫星的伪距信息,进行伪距单差差分。以伪距差分信息作为观测量,以跟踪船相对目标船的位置信息作为状态量,建立了跟踪船相对目标船的位置信息解算模型,利用最小二乘法解算跟踪船相对目标船的位置信息,以满足编队舰船间的相对导航信息需求。将相对位置信息解算模型和方法应用于实测试验,数据处理结果表明,相对距离测量精度优于0.2 m,方位精度优于5°,相对距离信息完全满足了舰船相对导航的需求,相对方位信息基本满足舰船相对导航的需求。     

An automatic and interactive large-deformation measurement system based on image processing

This paper describes an image-processing-based measurement system by which an automatic large deformation characterization and interactive force control can be realized. The system is provided by a servo-controlled CCD camera and a PC-based frame grabber. A tracking procedure based on the location of a target point is employed for guiding the camera movement. It is intended to monitor the local deformation in a relatively small moving area containing small globules. The globule positions are then used to determine the surface deformation characteristics. In this system, the momentary principal strains being computed online are immediately used to control the applied force. As an illustration, the present system is applied for observing a long-term homogeneous large deformation in SI-rubber specimens being subjected to a constant uniaxial true stress. Four solid, minuscule, relatively undeformable polystyrene globules are used as markers. A true stress control algorithm is developed based on the isotropy assumption in which the transverse area normal to the loading direction becomes determinable from the surface deformation data. It can be stated that the maximum speed of the true stress control is mainly related to the speed of image processing and analysis, which in turn is related to the chosen number of globules and the performance of the PC used. By using four globules, the true stress readjustment could be accomplished for roughly every 4 s. For a large-strain deformation of SI-rubber, it appears that the isotropy assumption is acceptable, since the resulting mean difference between out-of-plane contraction and in-plane contraction is restricted to about±8 percent.     

地基不均匀沉降对框架结构影响的有限元分析

利用ANSYS有限元程序分析某三层框架中柱柱脚不同沉降量作用下上部结构产生附加内力的规律.首先,定义"solid65"实体单元建立框架三维整体模型,分析的结果可以供子模型施加切割边界自由度约束时调用.其次,建立精密划分单元的三跨框架梁子模型.从梁纵向钢筋的应力分析结果可以看出,随着中间柱脚处沉降变形的增大,框架梁边柱支...     

A new subregion mesh method for the investigation of the elastic-plastic impact in flexible multibody systems

Impact processes between flexible bodies often lead to local stress concentration and wave propagation of high frequency. Therefore, the modeling of flexible multi-body systems involving impact should consider the local plastic deformation and the strict requirements of the spa-tial discretization. Owing to the nonlinearity of the stiffness matrix, the reduction of the element number is extremely important. For the contact-impact problem, since different regions have different requirements regarding the element size, a new subregion mesh method is proposed to reduce the number of the unnecessary elements. A dynamic model for flexible multibody systems with elastic-plastic contact impact is established based on a floating frame of reference formulation and complete Lagrange incremental nonlin-ear finite-element method to investigate the effect of the elastic-plastic deformation as well as spatial discretization. Experiments on the impact between two bodies are carried out to validate the correctness of the elastic-plastic model. The proposed formulation is applied to a slider-crank system with elastic-plastic impact.     

Nonlinear dynamics of one disk asymmetrical rotor supported by two journal bearings

Asymmetrical one disk rotor interacting with fluid films of short journal bearings is considered. Gyroscopic moments acting on a disk are taken into account. The forces of the journal bearing fluid film are derived analytically. The system of four nonlinear ordinary differential equations is obtained to study the rotor vibrations. The origination of self-sustained vibrations of rotor is studied by means of Shaw–Pierre nonlinear modes. The harmonic balance method is applied to study the self-sustained vibrations with large amplitudes.     

Formulation of Three-Dimensional Joint Constraints Using the Absolute Nodal Coordinates

A wide variety of mechanical and structural multibody systems consist ofvery flexible components subject to kinematic constraints. The widelyused floating frame of reference formulation that employs linear modelsto describe the local deformation leads to a highly nonlinear expressionfor the inertia forces and can be applied to only small deformationproblems. This paper is concerned with the formulation and computerimplementation of spatial joint constraints and forces using the largedeformation absolute nodal coordinate formulation. Unlike the floatingframe of reference formulation that employs a mixed set of absolutereference and local elastic coordinates, in the absolute nodalcoordinate formulation, global displacement and slope coordinates areused. The nonlinear kinematic constraint equations and generalized forceexpressions are expressed in terms of the absolute global displacementsand slopes. In particular, a new formulation for the sliding jointbetween two very flexible bodies is developed. A surface parameter isintroduced as an additional new variable in order to facilitate theformulation of this sliding joint. The constraint and force expressionsdeveloped in this paper are also expressed in terms of generalizedCholesky coordinates that lead to an identity inertia matrix. Severalexamples are presented in order to demonstrate the use of theformulations developed in the paper.     

电流变液滑动轴承的数值研究

基于油膜内屈服面位置可能出现的4种情况，Tichy提出了用于Bingham流体滑动轴承特性及其屈服面位置的计算方法，在将该计算方法推广到电流变液滑动轴承的计算时，发现随着外加电场强度的变形，出现了轴承风屈服面位置不变的非物理结果，而且Tichy的方法只能适用于无限宽滑动轴承，为了对有限宽度的电流变液滑动轴承进行数值研究，采用了类Bingham模型，通过差分离散和超松驰迭代的方法对雷诺方程进行求解，计算结果表明：电流变流滑动轴承内的压力分布可以通过外加电场强度来控制，轴承间隙内屈服面位置随电场强度变化而产生的移动是使轴承润滑性能得以改变的重要力学机制；在轴承以高剪切速率运转时，由于电流变液表观黏度随电场强度的变化已经很小，该机制在轴承的设计中尤为重要。     

An approach for calculating the dynamic load of deep groove ball bearing joints in planar multibody systems

This study is focused on dynamic modeling of planar multibody systems with multiple deep groove ball bearing joints, in which the radial clearance, contact deformation, and bearing kinematics are included. By using the approach presented, the variation of the joint reaction force and the dynamic load on each ball element in bearings can be simulated. The deep groove ball bearing joints are modeled by introducing a nonlinear force system, which takes into account the contact elastic deformations between the ball elements and the raceways. The contact force is calculated by the Hertzian contact deformation theory that accounts for the geometrical and material properties of the contacting bodies. A planar slider-crank mechanism with two deep groove ball bearing joints is chosen as an example to demonstrate the application of the methodologies presented in this paper. In this model, one bearing locates at the joint between the ground and crank, while the other one locates at the joint between the crank and connecting rod. By numerical calculation, the dynamic load distribution characteristics of bearings under real mechanism movement conditions are simulated. From the results, it can be concluded that the dynamic load on each rolling element varies differently and belongs to a variable load with the change of mechanism configuration. Load characteristic analysis is the foundation of developing research on the fatigue life and reliability of bearings. This study will provide a key mechanical support for the performance evaluation, dynamic design, and geometrical parameter optimization of the joint rolling element bearings.     

Topological approach to solve frame structures using topological collections and transformations

The present work tackled the modeling of frame structures using a topological approach based on the concepts of topological collections and transformations. The topological collections are used to specify the interconnection law between the frame structures and the transformations that are used to describe their behavior. As a language allowing the application of this approach, we applied the MGS (Modeling of General System) language. To validate this approach, we studied the case of two- and three-dimensional frame structures. Then, the results obtained using the MGS language are presented and compared to those obtained by the structural calculation software by the finite-element method RDM6. For both studied cases, we find that the results obtained by MGS language based on the notions of topological collections and transformations and those obtained by the RDM6 software based on the finite element method are very close, which validates our approach. Using this topological approach, any structure can be characterized by local relations between its elements, thus making it possible to dissociate its topology and its physics. Indeed, in our topological approach, we separately define the topology of the studied frame structure and the local behavior law as well as the equilibrium equations of its various components. Therefore, this topological approach might be generalized to model complex systems which can be considered as a set of local elements linked by a neighborhood relationship.     

穿斗式木框架受力性能研究

为研究西南地区穿斗式木结构的承载能力和变形特征,设计了单榀足尺穿斗式木框架进行水平静力单调加载试验,获得了木框架水平荷载-位移曲线关系以及木框架的整体破坏形态等,并采用ABAQUS 软件对木框架进行数值分析．研究表明木框架破坏形式表现为框架整体的严重倾斜,柱与枋本身较为完好;木框架柱顶侧移随着加载位移的增加呈线性增长关系,对称的左右立柱和瓜柱柱顶侧移基本一致;不同节点榫头同步拔出,拔榫量峰值相差较小,表现出较好的协调性;暗销节点的变形主要表现为榫头的挤压凹陷,榫头横纹方向较早地进入塑性变形阶段．卯口受压变形较小,处于弹性变形阶段．     

预应力混凝土平面杆系结构的有限元方法

建立了基于有限元方法的考虑材料和几何非线性的任意截面预应力混凝土平面杆系结构的数值分析模型,可用于模拟预应力混凝土大跨度梁、单向偏压细长柱等的非线性全过程结构响应。引入修正的Rodriguez截面模型确定截面切线刚度,其中混凝土的贡献通过截面边界顶点定义的梯形单元来实现;在此基础上利用传统的平面非线性杆单元导出了标准有限元公式。通过两个算例验证了该模型的可靠性和适用性。     

海洋平台导管架结构分析中管节点局部柔度的等效单元

本文建立了一种在海洋平台导管架有限元分析中代表管节点局部柔度的等效单元,可有效地反映管节点在轴力和弯矩作用下的局部变形性质,并导出了T型、Y型以及K型管节点的局部柔度等效单元的刚度矩阵。本文建立的等效单元可方便地与通用结构分析有限元程序(如SAP5)配合,对海洋平台导管架进行计及管节点局部柔度的精确静动力分析。作者编制了与SAP5配合使用的前处理程序,可自动生成符合SAP5输入格式的等效单元读入刚度矩阵的数据。文中给出了说明等效单元应用方法的简单算例。与有限元法计算的结果比较表明,用等效单元模拟管节点的局部柔度是必要的和准确可行的。     

Frame analysis with panel zone deformation

Conventional analyses of frameworks are usually carried out without considering the effect of panel zone deformation on frame behavior. As a result, center-to-center distances rather than clear spans are used for the lengths of the members. As is evident from experimental studies, the effect of panel zone deformation has a pronounced influence on frame behavior. In particular, the strength and drift of the frame will be affected if panel zone deformation is taken into consideration in the analysis. In this paper, various deformation modes of the panel zone are identified. A simple model which can be used to represent all these modes is then presented. The validity of this model is established by comparison with experiments on joint subassemblages. Finally, a two-bar frame with different behavioral joint models is analyzed numerically to demonstrate the importance of using realistic models in frame analysis.