滚动接触疲劳载荷对铁轨表面接触疲劳裂纹应力强度系数的影响

为研究轮轨滚动接触疲劳(Rolling Contact Fatigue,RCF)载荷对铁轨表面裂纹应力强度系数的影响,以UIC60铁轨轮廓尺寸为依据建立轮轨接触的三维有限元模型,通过改变RCF载荷大小、轮轨表面摩擦因数和接触中心位置等轮轨接触的输入参数,计算铁轨表面接触裂纹尖端的应力强度系数,分析RCF载荷对铁轨表面接触疲劳裂纹的影响.结果表明RCF载荷作为控制铁轨表面接触裂纹的重要因素,其变化直接导致裂纹尖端应力强度系数的变化,从而改变裂纹的扩展状况.为减缓铁轨表面裂纹的扩展,可以针对载荷采取均匀分布载重量、使用润滑剂降低轮轨摩擦因数等相应措施.     

滚动接触疲劳载荷对铁轨表面接触疲劳裂纹应力强度因子的影响

为研究轮轨滚动接触疲劳（Rolling Contact Fatigue,RCF）载荷对铁轨表面裂纹应力强度因子的影响,以UIC60铁轨轮廓尺寸为依据建立轮轨接触的三维有限元模型,通过改变RCF载荷大小、轮轨表面摩擦因数和接触中心位置等轮轨接触的输入参数,计算铁轨表面接触裂纹尖端的应力强度因子,分析RCF载荷对铁轨表面接触疲劳裂纹的影响. 结果表明RCF载荷作为控制铁轨表面接触裂纹的重要因素,其变化直接导致裂纹尖端应力强度因子的变化,从而改变裂纹的扩展状况;为减缓铁轨表面裂纹的扩展,可以针对载荷采取均匀分布载重量、使用润滑剂降低轮轨摩擦因数等相应措施.     

A multi-mesh MPM for simulating the meshing process of spur gears

A numerical scheme is presented to simulate the meshing process of spur gears, based on the material point method (MPM). To allow engagements at successive contact points and subsequent separation between neighboring gear teeth, a contact/sliding/separation procedure in a multi-mesh environment without using master/slave nodes is proposed so that the no-slip contact constraint inherent in the existing MPM can be released. Individual drive members rotate around corresponding axes, through which simulated angular velocity transmission is in good agreement with the analytical solution. It appears from the simulation results presented here that the multi-mesh MPM could become a robust spatial discretization tool for gear design problems that involve large rotation, contact/sliding and separation.     

Decision on economical rail grinding interval for controlling rolling contact fatigue

Rail players around the world have been increasing axle loads to improve the productivity of freight and heavy haul operations. This has increased the risk of surface cracks at curves because of rolling contact fatigue. Rail grinding has been considered an effective process for controlling these cracks and reducing risks of rail breaks. The complexity of deciding the optimal rail grinding intervals for improving the reliability and safety of rails is because of insufficient understanding of the various factors involved in the crack initiation and propagation process. This paper focuses on identifying the factors influencing rail degradation, developing models for rail failures and analyzing the costs of various grinding intervals for economic decision making. Various costs involved in rail maintenance, such as rail grinding, downtime, inspection, rail failures and derailment, and replacement of worn‐out rails, are incorporated into the total cost model developed in this paper. Field data from the rail industry have been used for illustration.     

Reducing bending stress in external spur gears by redesign of the standard cutting tool

For the design of gears the stress due to bending plays a significant role. The stress from bending is largest in the root of the gear teeth, and the magnitude of the maximum stress is controlled by the nominal bending stress and stress concentration due to the geometric shape of the tooth. In this work the bending stress of involute teeth is minimized by shape optimizing the tip of the standard cutting tool. By redesign of the tip of the standard cutting tool we achieve that the functional part of the teeth stays the same while at the same time the root shape is changed so that a reduction of the stresses results. The tool tip shape is described by different parameterizations that use the super ellipse as the central shape. For shape optimization it is important that the shape is given analytically. The shape of the cut tooth that is the envelope of the cutting tool is found analytically. The parameterization includes the standard ISO tooth. Practical simple changes in the design of the tool tip is shown to result in large reduction of the bending stress, keeping at the same time the engage part of the tooth unchanged. This leads to gears that have unchanged functionality based on the involute design, and these can be engaged with existing designs. The presented new cutting tools are custom tools specific for a given gear.     

直齿圆柱齿轮数字测量仪的设计与研究

介绍了基于计算机视觉技术的直齿圆柱齿轮数字测量仪,阐述了仪器的运行原理、硬件组织结构和软件功能模块,提出了齿轮基本参数的测量算法。首先利用图像处理技术提取图像精确边缘,然后利用改进的随机Hough变换确定齿轮中心,最后计算齿轮基本参数并存储于数据库中。实验结果表明,该仪器测量精度高、速度快、操作简便、自动化程度高,对齿轮精密制造和机械传动具有重要意义。     

A theoretical numerical study of the rotational restraint in cold-formed steel single skin purlin-sheeting systems

Cold-formed steel purlins are commonly used in the construction of industrial buildings. The roof sheeting increases the strength of the attached purlin to a considerable extent by providing lateral and rotational restraints. Further, the rotational restraint plays an important role on the buckling behaviour of the attached purlin. There is a need for a design method that accurately predicts the rotational restraint without experimental tests. Addressing this problem, in this research work, a non-linear finite element model is developed to estimate the rotational restraint provided by the first and second generation trapezoidal sheeting to the attached purlin. This model is applicable to trough-fixed and crest-fixed single skin purlin-sheeting systems commonly employed in steel roofs. The performance of the finite element model is validated by conducting experimental tests and found to be in good agreement. The factors influencing the rotational restraint can be investigated by using this validated finite element model. It opens the way to the development of a design method for estimating the rotational restraint provided by the sheeting to cold-formed steel purlins.     

A short note for numerical analysis of dynamic contact considering impact and a very stiff spring-damper constraint on the contact point

By extending the numerical technique suggested by the author for the dynamic contact problem having a very stiff spring on the contact point, it is shown that the dynamic contact problem having a very stiff damper as well as a spring on the contact point can be time integrated without instability by imposing the time-differentiated constraints with the unconditionally stable Newmark time integration rule. It is also shown that the dynamic contact involving the repeated impacts and separations can be solved without instability by using the same time-differentiated constraints, and that the spring-damper deformation (i.e., penetration) on the contact point at the time of impact (i.e., at the first time step of contact) can be most reasonably determined by the displacement contact constraint. The special features of the present technique to solve the impact problem having a very stiff spring-damper on the contact point are that the equation of motion may be time integrated with any convenient ODE technique, and that the time step size reduction or the penetration threshold need not be considered at the time of impact.     

燃料电池轿车变速器齿轮接触应力分析及疲劳寿命计算

为有效分析燃料电池轿车变速器齿轮接触应力以及更精确地计算齿轮的疲劳寿命,满足齿轮的使用要求,建立齿轮三维模型,应用有限元方法结合变速器实际载荷谱对齿轮接触应力进行仿真计算.根据计算结果,应用齿轮有限寿命设计理论对齿轮疲劳寿命进行计算,得到齿轮的接触应力和疲劳寿命.该方法可以为燃料电池变速器齿轮接触应力分析和疲劳寿命计算提供参考.     

A multi-agent architecture for dynamic scheduling of steel hot rolling

Steel production is a complex process and finding coherent and effective schedules for the wide variety of production steps, in a dynamic environment, is a challenging task. In this paper, we propose a multi-agent architecture for integrated dynamic scheduling of the hot strip mill (HSM) and the continuous caster. The scheduling systems of these processes have very different objectives and constraints, and operate in an environment where there is a substantial quantity of real-time information concerning production failures and customer requests. Each process is assigned to an agent which independently, seeks an optimal dynamic schedule at a local level taking into account local objectives, real-time information and information received from other agents. Each agent can react to real-time events in order to fix any problems that occur. We focus here, particularly, on the HSM agent which uses a tabu search heuristic to create good predictive–reactive schedules quickly. The other agents simulate the production of the coil orders and the real-time events, which occur during the scheduling process. When real-time events occur on the HSM, the HSM agent might decide whether to repair the current schedule or reschedule from scratch. To address this problem, a range of schedule repair and complete rescheduling strategies are investigated and their performance is assessed with respect to measures of utility, stability and robustness, using an experimental simulation framework.     

Kinematics and control of multifingered hands with rolling contact

The kinematics of rolling contact are derived for two surfaces of arbitrary shape rolling on each other. The kinematic equations are applied to a multifingered hand manipulating some object of arbitrary shape in three dimensions, and a scheme is presented for the control of such a hand which is a generalization of the computed torque method of control of robot manipulators. In implementing the control, it is required that all applied forces lie within the friction cone of the object so that sliding does not occur. The theory has been validated by dynamic graphical simulations of the resulting closed-loop system for several examples     

A numerical study of compactons

The Korteweg–de Vries equation has been generalized by Rosenau and Hyman [Compactons: Solitons with finite wavelength, Phys. Rev. Lett. 70(5) (1993) 564] to a class of partial differential equations that has soliton solutions with compact support (compactons). Compactons are solitary waves with the remarkable soliton property that after colliding with other compactons, they re-emerge with the same coherent shape [Rosenau and Hyman, Compactons: Solitons with finite wave length, Phys. Rev. Lett. 70(5) (1993) 564]. In this paper finite difference and finite element methods have been developed to study these types of equations. The analytical solutions and conserved quantities are used to assess the accuracy of these methods. A single compacton as well as the interaction of compactons have been studied. The numerical results have shown that these compactons exhibit true soliton behavior.     

A new method for modelling and simulation of the dynamic behaviour of the wheel-rail contact

This paper presents a new method for modelling and simulation of the dynamic behaviour of the wheel-rail contact. The proposed dynamic wheel-rail contact model comprises wheel-rail contact geometry, normal contact problem, tangential contact problem and wheelset dynamic behaviour on the track. This two-degree of freedom model takes into account the lateral displacement of the wheelset and the yaw angle. Single wheel tread rail contact is considered for all simulations and Kalker s linear theory and heuristic non-linear creep models are employed. The second order differential equations are reduced to first order and the forward velocity of the wheelset is increased until the wheelset critical velocity is reached. This approach does not require solving mathematical equations in order to estimate the critical velocity of the dynamic wheel-rail contact model. The mathematical model is implemented in Matlab using numerical differentiation method. The simulated results compare well with the estimated results based on classical theory related to the dynamic behaviour of rail-wheel contact so the model is validated.     

钛合金结构疲劳损伤监测实验研究

飞机钛合金结构损伤的监测,对于保证飞行器的安全具有重要的意义。提出了一种涡流阵列传感器,并通过搭建监测系统,进行了TC4钛合金不同宽度裂纹扩展模拟监测实验研究。研究结果表明：当钛合金出现裂纹后,传感器各通道的输出信号与无裂纹的基准信号有较大的变化,并且随着裂纹宽度的增加,输出信号幅值比增大。同时,模拟监测实验研究表明：传感器能够准确地识别和定量监测裂纹,精度达到1mm。     

Generalized concept of meshing and contact of involute crossed helical gears and its application

A general approach for generation and design of standard and non-standard involute crossed helical gears is proposed. The conjugation of gear tooth surfaces is based on application of two generating rack-cutters with a common normal section. The investigation of the geometry is based on a new approach for presentation of the line of action A (the line of points of contact of tooth surfaces). Line A is represented in a plane Π that is tangent to the pinion base cylinder and position of A is determined analytically. Edge contact of tooth surfaces is avoided by limitation of shift of line of action caused by errors Δγ and ΔE of the crossing angle and the shortest distance, respectively. Simulation of meshing and contact is computerized by developed computer program. Enhanced stress analysis approach is proposed. The developed theory is illustrated with numerical examples.     

A numerical framework for load identification and regularization with application to rolling disc problem

Indirect identification methods are applied when direct measurement is unfeasible. One example is the measurement of the contact force between wheel and rail in railway traffic. This paper focuses on optimization-based methods for the identification of contact forces with the aim of developing a reliable and robust load identification scheme. A particular issue discussed here is the choice of discretization in space–time, enabling the sampling instances of the measurements, the parameterization of the sought input and the discretization of the pertinent state equations to be decoupled, in contrast to traditional methods such as, e.g. dynamic programming.In the present preliminary study where a 2-D disc is considered as a representative of a train wheel, a radial concentrated force rotates around the disc’s perimeter, representing the contact force acting on the rim of the wheel, while radial strains are measured on a set of points corresponding to the strain gauges position. The strain history data is then used in the identification procedure where the applied force is sought to minimize the discrepancy between the predicted and measured strain history. In particular the convergence of the results with respect to the temporal discretization of the model and the time parameterization of the sought loading history are investigated under the influence of noise. It is seen that choosing a discretization of the sought load that is coarser than that of the state variable gives a more robust scheme. The traditional Tikhonov regularization can also be added within the current framework. Furthermore, with the aid of a sensitivity analysis, the influence of measurement noise can be quantified.     

A comparison of adaptive control strategies for hot steel strip rolling mills

Many modeling situations occur in which the plant has uncertain dynamics, nonlinearities, time varying characteristics and noise corrupted input and output measurements. These processes generally require a human operator whose function is to provide intelligent modeling and control. This exact situation occurs in the modeling and control of roll force in a hot steel rolling mill. It is the purpose of this paper to investigate and compare various adaptive control strategies for this problem.The first strategy uses a parameter identification technique to track the parameters in the roll force setup model from one steel run to the next. The next algorithm provides feedback control from run to run by an adaptive controller which uses a linear reinforcement learning scheme to adjust its parameters. The third method accounts for the above complexities by approaching the problem from a behavioral and structural point of view. The behavior of the model is assessed through a performance evaluator and the model is modified structurally and parametrically to improve the performance of the system as the process evolves. The derivation is based on correlation techniques and linear reinforcement learning theory, the latter of which provides memory and intelligence to the algorithm to model the decision process of the human operator. The results of this work serve to reinforce the opinion that the nonlinear mathematical structure of the model should be able to change from one steel run to the next in order to compensate for changes in mill characteristics and in the mill environment. Modeling results are presented from actual mill data and comparisons are made with time invariant models. In addition, the algorithms are general enough so that they may be easily applied to other processes that seem to defy traditional modeling techniques. They are not case dependent.     

A numerical study on the damping capacity of metal matrix nanocomposites

In the present study, the damping capacity of metal matrix nanocomposites (MMNCs) is predicted using a micro-mechanical modeling approach. The model is based on finite element analysis of a unit cell, which mimics a pure metallic lattice with stiff reinforcing nanoparticles. The dissipated energy of nanocomposite is predicted numerically by applying a harmonic load on the unit cell model. The influences of the grain size, boundary phase thickness and reinforcement size on the energy dissipation were calculated by the developed finite element model. Also, the damping capacities of three typical particulate reinforced nanocomposites have been simulated by the proposed model. The relationship between damping capacity and dislocations were also discussed with respect to the Granato–Lücke (G–L) theory. The results calculated from the developed model show good agreement with the G–L theory, which demonstrates the feasibility of damping calculation with the proposed method.     

Aspects of the dynamic behaviour of steel members

A fortran computer program has been developed to analyse the elastic–plastic behaviour of steel structural members subjected to dynamic loading. The program uses an incremental numerical procedure in which the governing equations are formed by consideration of the structure's energy and integrated with respect to time by the Newmark method. Large deflections, shear deformation and strain-rate sensitivity are all taken into account.The program has been used to investigate the dynamic behaviour of mild steel beams and bars with a solid rectangular cross-section. The fundamental axial and flexural frequencies of several linear examples were determined and the elastic and elastic–plastic responses of bars to suddenly applied axial loads were investigated in detail.