炭/炭复合材料湿式制动过程中的温度场模拟

摩擦过程中的温度场和热应力分布状况是摩擦学研究领域的一个重要课题.基于炭/炭复合材料制动盘湿式制动试验,将制动过程中的摩擦生热等效为瞬时移动面热源,按传动学理论计算制动盘与冷却润滑油的对流传热系数,建立三维循环对称有限元模型,运用有限元软件ANSYS分析制动盘的温度分布,给出典型时刻的温度场分布云图及温度升高引起的热应力场.利用有限元分析刹车制动过程的温度场,可为摩擦材料的研制及制动盘的设计提供有效的参考.     

Theoretical Explanation of Uneven Transverse Temperature Distribution in Wide Thin Strip Rolling Process

 In this paper we propose a new theoretical thermo-mechanical explanation of the uneven transverse temperature distribution, along the width, for thin and wide hot rolled produced strip. In particular, we base our reasoning starting from the irregular pressure/friction distribution, that lead to an uneven heat generation. A 2-D mathematical model to calculate the transverse temperature distribution is presented, both to give a physical explanation to our problem, and to be used as an essential basis to build a correspondent FEM simulation model, in which heat loss and generation are both considered. Deformation and friction heat are both described in details, having a paramount importance in our reasoning. The heat generation problem is split into two parts, for a clearer and more logical analysis: one for the strip centre, and one for the sides, in correspondence of the temperature peak points at 100mm from the strip edge. Finally it is shown how our new theoretical model can lead to the exact interpretation of the measured uneven temperature distribution.     

热连轧轧辊瞬态温度场研究

考虑水冷、空冷、轧辊与轧件接触热传导等动边界条件，采用有限差分法，建立了热连轧轧辊瞬态温度场变步长分析计算模型。该模型能实现轧辊温度场的动态分析和精确计算，预测轧制时以及终轧后空冷的轧辊瞬态温度场。试验和仿真结果表明，所建立的分析计算模型考虑因素全面、合理，计算精度较高，计算值与实测值吻合良好，真实地反映了轧辊的温度变化情况。     

Coupled thermal and stress-strain models for the continuous casting of steels

During the continuous casting of steel thermo-mechanical loadings may cause defects of the strand shell when exceeding the temperature-dependent material strength. Primary cause is the interplay of temperature level, and temperature gradients within the strand shell, the change of material properties, and further mechanical loadings of the strand shell like compression and friction forces or the ferrostatic pressure of the liquid. A model system has been developed to calculate the temperature distribution during continuous casting of steel and the resulting probability of hot crack formation, due to the thermo-mechanical loadings. First part is a thermal model to calculate the three-dimensional transient temperature field. In a reduced form this model can describe two-dimensional transient and, with less effort, two-dimensional steady-state problems. For the calculation of stresses and displacements a model based on a simple plane strain formulation, and a model using the fully three-dimensional stress-formulation are shown. Because material behaviour and temperature field are interdependent, thermal and mechanical models have to be coupled depending on the problems to be solved. Strategies for a problem-specific model coupling are discussed. Finally, the applicability of the model system is shown by some example problems from operational practice.     

转炉减速器齿轮瞬态本体温度场分析

针对转炉减速器齿轮承载越来越高的现状,利用齿轮啮合理论、摩擦学、传热学、赫兹接触等理论,研究了齿轮的相对滑动速度及轮齿摩擦系数的变化规律,计算出了齿轮沿啮合线摩擦热流量。通过建立转炉减速器齿轮瞬态温度场有限元分析模型,获得了齿轮瞬态本体温度场,齿轮工作时间与温度梯度的关系表明越是能迅速达到热平衡状态,对转炉减速器齿轮传动越有利。该研究结果为转炉减速器齿轮的安全使用提供了理论依据,为以后转炉减速器齿轮瞬态本体温度场的快速建模和分析提供了方法。     

Numerical simulation of the molten-pool formation during the laser surface-melting process

The boundary-fixing method, by which the moving-boundary problem is reduced into the fixedboundary problem, has been applied to the numerical simulation of the molten-pool formation during the laser surface-melting process. A mathematical formulation and corresponding calculation scheme are developed for a model based on transient three-dimensional heat conduction with a moving solid-liquid interface. By the use of the boundary-fixing method, the heat balance at the solid-liquid interface is rigorously treated in the present numerical simulation. When the steady state is reached, the resulting molten pool is obtained without undulation in shape. The calculated results, based on an Al-32.7 wt pct Cu eutectic alloy, are discussed and compared with experimental data.     

铝合金圆棒挤压过程应力场模拟

以铝圆棒的挤压生产为研究对象,考虑了热传导、对流换热、摩擦生热、塑性功、热力藕合等多种条件,运用Marc软件中的刚塑性有限元分析软件研究了铝圆铸锭挤压生产圆棒过程,模拟分析了摩擦条件和挤压比对应力、应变的影响。     

Numerical Error in Weighting Function-Based Unsteady Friction Models for Pipe Transients

The accurate simulation of pressure transients in pipelines and pipe networks is becoming increasingly important in water engineering. Applications such as inverse transient analysis for condition assessment, leak detection, and pipe roughness calibration require accurate modeling of transients for longer simulation periods that, in many situations, requires improved modeling of unsteady frictional behavior. In addition, the numerical algorithm used for unsteady friction should be highly efficient, as inverse analysis requires the transient model to be run many times. A popular model of unsteady friction that is applicable to a short-duration transient event type is the weighting function-based type, as first derived by Zielke in 1968. Approximation of the weighting function with a sum of exponential terms allows for a considerable increase in computation speed using recursive algorithms. A neglected topic in the application of such models is evaluation of numerical error. This paper presents a discussion and quantification of the numerical errors that occur when using weighting function-based models for the simulation of unsteady friction in pipe transients. Comparisons of numerical error arising from approximations are made in the Fourier domain where exact solutions can be determined. Additionally, the relative importance of error in unsteady friction modeling and unsteady friction itself in the context of general simulation is discussed.     

简单断面型钢热轧过程的数值模拟

以在椭圆孔型中轧制方坯为例，采用全三维弹塑性大变形热力耦合有限元法来模拟简单断面型钢的热轧过程，分析并建立了热传导、接触和摩擦等边界条件模型，计算得到轧件形状、温度变化及变形等结果。而且数值模拟结果与实验结果吻合较好     

无缝钢管张力减径有限元模拟的摩擦模型及其应用

采用在轧辊和钢管之间附加一层动态接触摩擦单元的方法,建立了钢管张力减径过程有限元模拟的摩擦模型.通过判断摩擦单元与轧辊的接触或脱离情况(不必确定摩擦力的大小和方向),利用其剪切变形来模拟轧辊与钢管接触表面的摩擦作用,实现了钢管产品张力减径过程的快速准确预报.     

时速350 km高速列车用铜基闸片材料的摩擦性能

闸片是高速列车制动系统的核心部件,本文设计了350 km·h^–1高速列车用铜基闸片材料,对闸片进行了1∶1台架实验考核,重点分析了摩擦膜的性质及闸片的摩擦磨损性能.结果表明,研制闸片不仅具有优异的摩擦系数稳定性和低的磨耗,还具有不伤盘的特点.瞬时摩擦系数和平均摩擦系数均满足TJCL/307—2019标准的要求,摩擦系数稳定性为0.0015,250～380 km?h^–1制动速率范围内的摩擦系数热衰退仅0.027,在380 km?h^–1下的平均摩擦系数仍维持在0.35,平均磨耗仅0.06 cm³?MJ^–1.闸片优异的摩擦制动性能归因于形成了高强韧、低转移速率的摩擦膜.利用大粒径摩擦组元作为外部运动障碍钉扎摩擦膜.摩擦膜中的亚微米磨屑作为摩擦膜与对偶盘的啮合点,提供摩擦阻力,以保持高速制动时的摩擦系数.添加的易氧化组元为摩擦膜源源不断提供氧化物,研磨生成的纳米氧化物作为弥散相强化摩擦膜.通过多尺度颗粒的协同增强,实现了摩擦膜的动态稳定化,赋予了闸片优异的摩擦磨损性能.     

Simulation of Strip Rolling Using Elastoplastic Contact BEM With Friction

With rollers as elastic bodies and workpieces as elastoplastic bodies,the rolling problem can be viewed as a friction elastic-plastic contact problem.With fewer assumptions in the simulation of strip-rolling process,a boundary element method（BEM）for two-dimensional elastoplastic finite strain and finite deformation analysis of contact problems with friction was presented.All the equations for contact problems,which include multi-nonlinearities,were obtained.Incremental and iterative procedures were used to find contact pressure and friction stress.Moreover,initial strain rate algorithm and work-hardening material behavior can be assumed in the plastic analysis.Several examples were presented,and the results of contact pressure and friction stress were in excellent agreement with those of analysis.     

Thermoelastic Stability of Two Bonded Half Planes

This paper investigates the thermoelastic stability of two bonded half planes consisting of different materials, using a perturbation method. It is found that the conduction of heat across an interface between two dissimilar elastic bodies can cause thermoelastic instabilities within the system. This type of instability has been shown to occur for the case where two frictionless half planes are in contact. The characteristic equation governing the thermoelasticity stability of the two bonded half planes takes the same form as that of the two frictionless half planes, thereby having, qualitatively, the same stability boundaries. The significance of this investigation relates to civil and marine engineering applications in which sandwich or bimetallic plate construction may be applicable.     

阻燃钛合金摩擦着火热源模型及仿真分析

钛火是现代航空发动机的典型灾难性事故,压气机转子与静子的异常摩擦是其主要热源。采用动网格方法结合等效模型建立转子与静子试件的三维热-力-磨损耦合有限元模型,对不同摩擦接触压力和环境温度等条件下550℃阻燃钛合金TF550摩擦着火过程的温度场进行数值建模与仿真分析。结果表明,在室温、200 N摩擦接触压力条件下,TF550钛合金静子试件在7.2 s达到着火温度,此时转子试件温度仍维持在1 000 K,比静子试件低约900 K;当摩擦接触压力从200 N增大至400 N时,摩擦着火延迟时间为3.3 s;当摩擦接触压力提升至700 N时,着火延迟时间缩短至2 s以内;在823 K的环境温度下,静子试件的摩擦着火延迟时间为5 s,比室温下的摩擦着火延迟时间缩短了2.2 s;相对于环境温度的影响,摩擦接触压力对TF550钛合金摩擦着火升温速率的影响更大。     

Thermomechanical Behaviour of Dry Contacts in Disc Brake Rotor with a Grey Cast Iron Composition

The objective of this study is to analyse the thermal behaviour of the full and ventilated brake discs of the vehicles using computing code ANSYS. The modelling of the temperature distribution in the disc brake is used to identify all the factors and the entering parameters concerned at the time of the braking operation such as the type of braking, the geometric design of the disc and the used material. The numerical simulation for the coupled transient thermal field and stress field is carried out by sequentially thermal-structural coupled method based on ANSYS to evaluate the stress and deformations on disc surface including the contact pressure on the pads. The results obtained by the simulation are satisfactory compared with those of the specialized literature.     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

三合一减速电机在桥式起重机上的应用

武钢某厂桥式起重机大车行走机构大量采用三合一减速电机,在使用过程中需要注意变频器的电气制动与减速电机的电磁制动之间的配合,通过添加密封和防尘盖可以解决减速机的漏油问题,在维护制动器时需要注意保证间隙和及时清除摩擦粉尘。     

制动摩擦材料研究进展

制动摩擦材料利用运动表面相接触时所产生的摩擦阻力达到减速或终止运动目的,是运载机械中安全保障装置的重要组成部分。本文综述了半金属基、金属基及非金属基制动摩擦材料的研究现状及优缺点,介绍了熔铸法、粉末冶金法及三维编织法等制动摩擦材料制备方法,并从摩擦、磨损、热稳定性等方面分析了制动摩擦材料的关键特性。从研究状况可知,摩擦材料正向少纤维、无纤维型方向发展,高性能、环保型摩擦材料具有较大的发展优势。优化制备工艺、降低生产成本、提高性能、扩大应用领域将是未来制动摩擦材料的研究重点。     

Two-Dimensional Transient Temperature Field of Finish Rolling Section in Hot Tandem Rolling

Comprehensively considering the factors such as descaling cooling, air cooling, watercooling, frictional heat and deformation heat in gap of every stand, heat conduction betweenwork roll and strip etc, a model of two-dimensional transient temperature field of finish rollingsection in hot tandem rolling was built with finite difference method to calculate the temperaturefields of strip and work roll. So two-dimensional accurate analysis and calculation of strip tem-perature were realized, and the theoretical basis for predicting and controlling strip temperaturewas provided. The simulated results show that the model is practical and reliable.     

Inverse Estimation of Transient Heat Flux to Slab Surface

 The transient heat flux was calculated using a model for inverse heat conduction problems based on temperature measurements. The unknown heat flux was taken as an optimization variable and solved by minimizing the differences between the calculated temperatures and the measured ones. Several examples were given to show the effectiveness and the accuracy of the inverse algorithm in estimating the transient heat flux to a slab surface. The results show that the inverse approach can be applied in the steel industry or in other areas where the target of investigation is inaccessible to direct measurements or difficult to be directly modeled.