高速轧机工作界面非稳态混合润滑过程多因素耦合辊缝力学特性研究

综合运用摩擦润滑理论、流体力学理论、轧制理论,建立了考虑动态辊缝非稳态润滑过程多因素耦合轧制界面力学模型.该模型综合运用了基于非稳态润滑过程的界面摩擦模型、工作辊运动模型、辊缝应力分布模型构成的界面薄膜约束多因素耦合模型.系统分析了非稳态混合润滑状态下,当压下率和表面粗糙度为定值时不同时刻工作区压应力和摩擦应力的分布情况,以及压下率为定值时工作区压应力、摩擦应力随表面粗糙度和后张应力变化的情况.结果表明:在压下率和表面粗糙度为定值时,当具有较大的后张应力时,工作区压应力和摩擦应力却较低,同时压应力梯度和摩擦应力梯度也相当小,摩擦应力在入口和出口边缘处达到最大,当后张应力减小时,辊缝间压应力和摩擦应力增加,压应力梯度和摩擦应力梯度较大;在压下率为定值而表面粗糙度为变量时,当后张应力较大时,表面粗糙度对工作区中的压应力和摩擦应力影响非常大,辊缝间压应力和摩擦应力随着表面粗糙度的增加而增加,当后张应力较小时,表面粗糙度对工作区中的压应力和摩擦应力影响不太明显.     

界面闪温对ZDDP反应膜生成特性的研究

二烷基二硫代磷酸锌(ZDDP)作为最常见的发动机润滑油添加剂,通常认为ZDDP摩擦膜在较高的宏观环境温度下产生,而忽视了局部区域的闪温变化对于膜生长的影响. 本文作者结合应力促进的热活化理论和润滑界面闪温计算模型,以球-盘滑滚摩擦试验研究为主,进行了界面闪温对ZDDP摩擦膜生成特性的分析. 在载荷和环境温度恒定的条件下,计算了不同界面滑滚比的闪温大小与分布,采用球-盘试验测得了常温下不同滑滚比的ZDDP润滑剂摩擦系数变化趋势,并与计算得到的闪温模型对照,得到闪温对ZDDP反应膜生长的影响规律;为了改善ZDDP薄膜导致的高摩擦,测试了硬脂酸钙与ZDDP的协同减摩效果. 结果表明:界面闪温的升高同样可以促进一定厚度的ZDDP摩擦膜生长;硬脂酸钙润滑剂与ZDDP共同生成的边界膜可以有效地降低ZDDP带来的高摩擦力,可以用于改善ZDDP摩擦膜的摩擦性能.      

Mathematical model for cold rolling based on energy method

There is an increasing requirement for improved accuracy of the rolling models which are widely used in rolling plant in order to produce high-quality products, because this accuracy is important for rolling schedule setup and automatic control. A three-dimensional mathematical model for cold rolling using tangential velocity field and energy method is firstly proposed to investigate the deformation of the strip at the roll gap based on elastic and plastic mechanics. The field and geometrical approximation yield criterion are used to integrate the internal plastic deformation power. The friction power is analyzed using the co-line vector inner product method. Finally, the analytical expressions of roll separating force and roll torque are obtained quickly considering the effect of roll flattening on the roll separating force. The predicted roll separating forces are consistent with other researchers’ models, especially for on-line measured roll separating forces in a tandem cold rolling plant. The accurate predicted results provide valuable guidelines for optimization of rolling process.     

Hydraulic analysis of free-surface flows with solidification

Summary The paper is concerned with a one-dimensional analysis of plane open-channel flow with continuous solidification. The process is of relevance for recent developments in the casting of steel and other metals. The bottom of the channel consists of a rotating casting roll and a horizontal cooling table, where the solidified material is withdrawn with given velocity. The study is restricted to the region downstream of the top of the casting roll. Surface tension is neglected. In the main part of the analysis inviscid fluid flow is considered since the Reynolds number is very large in the applications. It is found that the steady-state solutions are nonunique in a certain parameter range. In addition to a continuous solution, there are two solutions including hydraulic jumps, with one hydraulic jump being located on the casting roll, the other one on the cooling table. Regarding the stability of the non unique solutions, the evolution of disturbances is investigated numerically as an initial-value problem. It is concluded that the hydraulic jump on the cooling table is unstable, while the other discontinuous solution as well as the continuous solution are stable for sufficiently small disturbances. Which stable solution is attained in the steady state, depends on the history of the process. Friction at the liquid/solid interface is taken into account in the last part of the analysis. A constant friction coefficient is assumed. It is found that the history of the process determines the steady-state solution if, and only if, the friction coefficient is sufficiently small. For larger values of the friction coefficient, the steady-state solution is unique and independent of the history of the transient process. Furthermore, for sufficiently large friction coefficients, stable hydraulic jumps are found, in contrast to the inviscid case, also on the cooling table. Received 19 March 1999; accepted for publication 3 May 1999     

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在重轨万能轧制过程中,首先建立了简化的三维理论模型. 然后分别给出了轨腰、轨头及轨 底的运动学许可速度场以及相应的应变速度场和剪应变速度强度,并求出了相应变形区的塑 性变形功率、速度间断面上消耗的功率以及由于摩擦产生的摩擦功率. 最后根据上限原理分 别求解了水平辊和两个立辊的轧制力上限解. 通过比较可知,二辊轧制理论公式误差很大因 此不能用于万能轧制过程,而上限法求得的轧制力近似解大于轧制现场数据但最大误差不超 过13\%, 因此根据上限原理进行轧制工艺参数设定及优化是比较可靠的.     

On the history of the dry friction law

We discuss the role played by Amontons, Coulomb, Leonardo daVinci,Morin, and Euler in the discovery of the dry friction law. In particular, reference is given to Euler’s 1748 paper,where an exhaustive statement of the dry friction law was given 37 years before Coulomb’s main publications. Painlevé’s criticism of the Coulomb law is assessed, and the main points of the theory of polycomponent dry friction are given.     

平移断层的倾角对地震产生的影响

利用边界单元法和滑移弱化摩擦本构关系分析了平移断层上地震的产生。从依赖于速率和状态的摩擦本构关系出发,通过忽略速度的影响得到了滑移弱化摩擦本构关系。建立了两种本构关系之间的联系,使得在两种模型中可以使用共同的参数。通过将地球表面模拟成一个包含在无穷大弹性介质中的无穷大裂纹,已有的边界积分方法可以直接用来分析断层的滑移。由于断层上的摩擦本构关系的非线性,得到的方程也是非线性的,采用牛顿迭代法进行求解。通过数值计算得到了平移断层上滑移位移、速度及摩擦力的分布规律。考察了平移断层的倾角对地震产生的影响,计算结果表明断层的倾角越小,地震产生的位置离地球表面越近且地震产生所需滑移的时间越短。     

An experimental investigation of roll waves in high pressure two-phase inclined pipe flows

This paper examines the effects of small upward inclinations on the formation of roll waves and the properties of fully developed roll waves at high pressure conditions. A total of 984 experiments were conducted at six positive pipe inclinations θ = 0.00°, 0.10°, 0.25°, 1.00°, 2.50° and 5.00° using a 25 m long 10 cm i.d. pipe. Sulfur hexafluoride (SF₆) was used at 8 bara giving a gas density of 50 kg/m³. Two independent mechanisms for the formation of roll waves were identified; (1) interaction between 2D shallow water waves and (2) a visible long wavelength instability of the stratified layer. Viscous long wavelength linear stability analysis predicted the critical liquid flow rate and liquid height for the initiation of roll waves when roll waves were formed due to the second mechanism. A simple equation from shallow water wave theory agreed with measurements for critical liquid flow rate when roll waves were formed due to the first mechanism. Shallow water wave speed agreed with critical wave speeds at transition and nonlinear wave speeds for fully developed roll waves in certain cases. The increase in interfacial friction due to the presence of large waves was compared with models from the literature.     

A set-valued force law for spatial Coulomb–Contensou friction

The aim of this paper is to develop a set-valued contact law for combined spatial Coulomb–Contensou friction, taking into account a normal friction torque (drilling friction) and spin. The set-valued Coulomb–Contensou friction law is derived from a non-smooth velocity pseudo potential. A higher-order Runge–Kutta time-stepping method is presented for the numerical simulation of rigid bodies with Coulomb–Contensou friction. The algebraic inclusion describing the contact problem is solved with an Augmented Lagrangian approach. The theory and numerical methods are applied to the Tippe-Top. The analysis and numerical results on the Tippe-Top illustrate the importance of Coulomb–Contensou friction for the dynamics of systems with friction.     

HC轧机辊间接触与辊系变形的Taylor级数多极边界元数学规划解析

分析HC轧机辊间接触分布和辊系弹性变形对于改善辊间压力分布状态,减少轧故褂檬倜案纳瓢逍畏浅Ｖ匾?醯捎诩扑懔亢艽?使用传统数值方法(有限元法或边界元法)分析辊间接触和辊系变形是非常困难的.本文描述了一种基于点-面接触模型的三维弹性接触Taylor级数多极边界元法,给出了数学规划解析方法,适合大规模弹性接触问题的求解....     

盘式制动器摩擦噪声特性的试验分析

盘式制动器制动时产生的摩擦噪声不仅影响车辆的驾乘舒适性,还会带来严重的环境噪声污染. 摩擦噪声具有瞬时性与不确定性的特点,至今尚未形成对制动器摩擦噪声机理的统一论断. 基于盘式制动器声振试验台,研究了摩擦系数、摩擦力波动系数和等效A声级三个参数在不同制动压力和制动初速度下的变化规律,结合对摩擦片微观特性的试验分析,从摩擦学角度揭示了盘式制动器摩擦噪声的发生规律及机理. 结果表明:摩擦噪声随制动初速度的增大而减小,随制动压力的增加而先增大后减小;制动摩擦噪声由于摩擦系统不稳定而产生,其产生原因是因为摩擦副表面的沟壑与黏着引起,沟壑与黏着程度与噪声的声压与频率呈正相关关系. 研究结果对于解释制动器摩擦噪声发生机理、控制制动器噪声污染具有重要理论意义和实际价值.      

Self-sustained slip pulses of finite size between dissimilar materials

The problem of a steady-state slip pulse of finite size between dissimilar materials is studied. It is shown that for a Coulomb friction law, there is a continuous set of possible solutions for any slip propagation velocity and any slip length. These solutions are, however, nonphysical because they show a singular behaviour of the slip velocity at one extremity of the pulse, which implies a crack-like behaviour. In order to regularize these solutions, we introduce a modified friction law due to Prakash and Clifton (Experimental Techniques in the Dynamics of Deformable Solids, Vol. AMD-165, pp. 33-48; J. Tribol. 120 (1998) 97), which consists in introducing in the Coulomb friction law a relaxation time for the response of the shear stress to a sudden variation of the normal stress. Then, we show that even for a slip velocity-dependent characteristic time, the degeneracy of the solutions is not suppressed and a physical pulse is not selected. This result shows the absence of steady state self-healing pulses within the modified friction law and is consistent with recent finite-difference calculations (J. Geophys. Res. 107 (2002) 10).     

Homogenization in non-linear dynamics due to frictional contact

This work is devoted to a study of the classical homogenization process and its influence on the behavior of a composite under non-linear dynamic loading due to contact and friction. First, the general problem of convergence of numerical models subjected to dynamic contact with friction loading is addressed. The use of a regularized friction law allows obtaining good convergence of such models. This study shows that for a dynamic contact with friction loading, the classical homogenization process, coupled with an homogenization of the frictional contact, enables replacing the entire heterogeneous model by a homogenized one. The dynamic part of the frictional contact must be homogenized by modifying the dynamic parameter of the friction law. Modification of the dynamic parameter of the friction law is function of the type and regime of instability. A calculation of a homogenized friction coefficient is presented in view to homogenizing the static part of the frictional contact when the friction coefficient is not constant over the contact surface. Finally matrix and heterogeneities stresses in the heterogeneous models are identified by using the relocalization process and a frictional contact dynamic analysis of a homogeneous model.     

Empirical dry-friction modeling in a forced oscillator using chaos

The coefficient of friction is measured during relative oscillation between sliding surfaces. Measurements are made during regular oscillations in which the excitation has a modulated amplitude, and during chaotic oscillations in which the excitation amplitude is fixed. The friction force is measured for paper on paper, and titanium on titanium. A friction law is derived based on observations from the measurements. This friction law is applied to a simulation model of an experimental forced oscillator. The simulated and experimental oscillators have similar qualitative dynamical features in the phase space.     

Stability of roll waves in open channel flowsStabilité de trains d'ondes dans un canal découvert

The stability of finite amplitude roll waves that may develop at a liquid free surface in inclined open channels of arbitrary cross-section is studied. In the framework of shallow water theory with turbulent friction the modulation equations for wave series are derived and a nonlinear stability criterion is obtained. To cite this article: A. Boudlal, V.Yu. Liapidevskii, C. R. Mecanique 330 (2002) 291–295.     

应变硬化薄板夹持型滚弯成形过程分析

现存文献对薄板的连续滚弯成形过程的数学模拟多限于讨论三辊轮解锥型弯板过程,且基于较多的假定和板的小变形情况。而开发有更多的功能和更高的生产效率的四辊轮连续弯板机需研究夹持型滚弯成形过程。本文将「１」的工作,理想塑性材料平面应变薄板的夹持型连续滚弯成形过程的弹塑性大变形弯曲的力学分析,推广至一般应变硬化材料的情形。得出了控制微分方程的解析解。采用固支边界条件模拟刚度很大的平持系统对板的夹持。通过对线     

The frequency response of dynamic friction: Model comparisons

Any linearised theory of the initiation of friction-excited vibration via instability of the state of steady sliding requires information about the dynamic friction force in the form of a frequency response function for sliding friction. Recent measurements of this function for an interface consisting of a nylon pin against a glass disc are used to probe the underlying constitutive law. Results are compared to linearised predictions from the simplest rate-state model of friction, and a rate-temperature model. In both cases the observed variation with frequency is not compatible with the model predictions, although there are some significant points of similarity. The most striking result relates to variation of the normal load: any theory embodying the Coulomb relation F∝N would predict behaviour entirely at variance with the measurements, even though the steady friction force obtained during the same measurements does follow the Coulomb law.     

Adaptive robust control methodology for active roll control system with uncertainty

The active roll control system (ARCS) can impose anti-roll moment quickly to prevent the vehicle rolling when the vehicle generates the roll tendency and effectively enhance the vehicle dynamic performance without sacrificing the ride comfort. In the dynamic model of the ARCS, the sprung mass of the vehicle is considered to be the uncertain parameter, which is (possibly) fast-varying. However, what we know about the uncertainty is just that it is bounded. Furthermore, the bound is unknown. The target roll angle is regarded as the constraint when the vehicle equipped with the ARCS is running under a given case. Taking the parameter uncertainty and possible initial condition deviation from the constraint into account, an adaptive robust control scheme based on the Udwadia and Kalaba’s approach is proposed to drive the ARCS to follow the pre-specified constraint approximately. The adaptive law is of leakage type which can adjust itself based on the tracking error. Numerical simulation shows that by using the adaptive robust control scheme, the error between the actual roll angle and the desired roll angle converges to zero quickly in 0.3 s from initial error 0.287 deg, and the final error is of the order of \(10^{-7}\). Thus, the control design renders the ARCS practically stable and achieves constraints following maneuvering.     

Transient response of a ship to an abrupt flooding accounting for the momentum flux

Numerical non-linear time domain simulation method for damaged ship motions is presented. Floodwater motion modelling is based on the lumped mass method with a moving free surface. The ship and floodwater motions are fully coupled. The variation of the floodwater mass is accounted for. A model to account for the flooding ingress transporting the momentum is presented. The experiments of abrupt flooding have shown that the ship may experience the first large roll towards the undamaged side, especially when a large undivided compartment is flooded. The presented time domain model is validated against the experimental data on the roll damping of the flooded ship and transient flooding. Two different initial stability conditions and two different compartment layouts are studied. Viscous dissipation of the floodwater motions is modelled with an equivalent friction coefficient. The impact of the viscous damping is studied. Transient flooding tests show that the inflow momentum has to be accounted for when the undivided compartment is flooded. The simulation model is capable of capturing the impact of the inflooding jet and the first roll on the opposite side of the damage is reproduced.