Coupled Thermo-Mechanical and Wear Effects on the Analysis of High Speed Railway Brake Systems

The high speed railway brakes transfer a large amount of kinetic energy into heat. The temperature during a brake operation could reach values higher than 90 °C. The dynamics of the brake system is rather complicated with respect to the multiphysical phenomena. In this paper, the thermo-mechanical coupling are investigated combined with the loos of brake material due to wear. The coupled model is discretized by conventional finite element method. Different coupled algorithms have been tested. Various scenarios have been simulated and shown reasonable results. The temperature and deformation on pad and disc, especially the thermal deformation of disc the so–called coning effect can also be prescribed with this coupled multiphysics model. Furthermore, the tapered wear on brake pads is also discussed as a requirement of railway brake design in terms of durability. Thereby, the Ehlers's model is normally used to minimize tapered wear by selecting an adequate point of applied braking force. An extended Ehlers's model is also presented here, which concerns wear effect based on Archard's model. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Cyclic Thermomechanical Coupled Problem of Thermal Gradients in Friction Railway Disc Brakes

The emergency braking distance of a TGV train at a speed of 320 km/h is almost 3000 m. Dry running brakes are reliable due to their predictable response to external stress and are thus used in such applications. The kinetic energy is dissipated proportionately into the brake disc and brake pad. This induced dissipation of energy and the high frequency of brake application cause high temperatures. These immense temperature changes could cause macroscopic cracks leading to failure of discs and accidents [1]. Generally, hot spotting describes the development of thermal localizations and can lead to early damage, early wear, pad performance loss, and squeal noise [2]. The aim of the present study is to improve a disc-pad transient numerical model by use of a coupled thermomechanical method. It is based on full 3-d thermomechanical calculations taking disc rotation into account. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of the temperature and wear behaviour of a disc brake

Aerosols are defined in the simplest form as a mixture of solid or liquid particles suspended in a gas [1]. Brake dust is an aerosol, generated as a result of erosion between brake disc and brake pad. The aerosols can cause visual disorder, heart and lung diseases, short term acute symptoms like asthma, bronchitis and long term chronic irritation and inflammation of the respiratory track, which can lead to cancer. Therefore, it is important to know which factors are affecting the erosion rate of brakes. The main objective of this work is to measure the erosion rate of brake discs and brake pads, depending on temperature changes and deformation by performing experiments and simulations at varying velocities and load conditions. The general purpose, commercially available finite element solver Abaqus is used for performing the thermomechanically coupled simulations. Archad's Wear Law is used for the wear calculation. Experiments are conducted by using a pin on disc test bench. Temperature changes are measured by using thermocouples and erosion rates by measuring the total volume loss. At the end, relationships between erosion rates and temperature changes for different brake disc velocities and load conditions are investigated and experimental and simulation results are compared and discussed. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A model of the relay valve used in an air brake system

The mathematical model governing the response of the relay valve in an air brake leads to a hybrid system in which different governing equations apply to different phases of the response of the air brake. To accurately describe the brake’s response characteristics it is imperative to take into account this hybrid structure, and it is to this aspect of the problem that this paper is addressed. The safe operation of any vehicle on the road depends, amongst other things, on a properly operating brake system. Most commercial vehicles such as trucks, tractor–trailers, buses, etc., are equipped with an air brake system. Any defect in a brake system can degrade its performance seriously and can lead to accidents. It is desirable and also important to develop systems that can control and diagnose air brake systems in order to both sustain and improve their performance. One approach to develop such systems is by obtaining a model of the air brake system and then using the same in the design process. The air brake system currently used in commercial vehicles can be broadly divided into a pneumatic subsystem and a mechanical subsystem. One of the main components in the pneumatic subsystem is the relay valve which operates the brakes on the rear axles of a tractor and the axles of a trailer. A relay valve has different modes of operation and the pressure response of the relay valve can be naturally described as the response of a hybrid system. In this article, we develop a hybrid dynamical model to predict the pressure response of the relay valve. An air brake testing facility has been set up at Texas A&M University and this model will be corroborated against experimental data obtained from the same.     

The numerical modelling of DC electromagnetic pump and brake flow

The interaction of an externally imposed magnetic and electric field on the laminar flow of a conducting fluid in a channel is studied using computational techniques. The Navier-Stokes equations and the equations describing the electromagnetic field are solved simultaneously in a single control volume-type computational fluid dynamic code, in a moderate Hartmann number and interaction parameter regime. The flow considered is two-dimensional, with an imposed magnetic field acting in the third dimension over the central region of the channel and decaying exponentially in the remainder. A pair of electrodes placed at right angles to the magnetic field exercises control over the resultant Lorentz force and hence the velocity profile shape. This configuration has application in direct-current electromagnetic pumps or, conversely, electromagnetic brakes. The initial parabolic flow profile acquires an M-shape / W-shape mode in the magnetic field fringe regions, corresponding to a pump / brake. A novel coupled procedure is described to model magnetohydrodynamic phenomena and is used to explore the effects of the Reynolds number, interaction parameter, and applied voltage on the pump / brake configuration.     

Characterization of disk brake noise behavior via measurement of friction forces

Squealing of disk brakes is a major problem in the field of vehicle design. It is commonly acknowledged, that this squeal is initiated by instability due to friction forces between the pads and the disk, leading to self excited vibrations. This work addresses the mechanical work of these friction forces in order to draw conclusions for the investigation of the noise behavior of disk brakes. Therefore a multi degree of freedom model is used to compare its stability behavior with the frictional work at the pads. The results obtained are applied to experiments in which, on the one hand brake pads with integrated piezoceramic actuators cause a broad band excitation and, on the other hand, dynamic pad velocities/accelerations and friction forces are measured. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of quasi-dimensional combustion model for predicting diesel engine performance

In order to improve the precision of quasi-dimensional combustion model for predicting diesel engine performance and promote the real time operating performance of the simulation model, a new phase-divided spray mixing model is proposed and the quasi-dimensional combustion model of diesel engine working process is developed. The software MATLAB/Simulink is utilized to build the quasi-dimensional combustion model of diesel engine working process, and the performance for diesel engine is simulated. The simulation results agree with experimental data quite well. The comparisons between them show that the relative error of power and brake specific fuel consumption is less than 2.8% and the relative error of nitric oxide and soot emissions is less than 9.1%. By utilization of this simulation model with personal computer, the average computational time for one diesel engine working process is 36 s, which presents good real time operating performance of the model. At the same time, the influence of parameters in calculation of air entrainment on prediction precision of diesel engine’s simulation model is analyzed.     

Evaluation of automotive disk brake noise behavior using piezoceramic actuators and sensors

One problem of disk brakes is the occurence of noise. This work in particular addresses the occurrence of disk brake squeal with frequencies from 1 up to 12 kHz which does generally not affect the basic functionality of the brake. Nevertheless it is a serious comfort problem and it causes a high amount of costs to design noiseless brake systems. This work examines methods to evaluate the noise behaviour of disk brakes using piezoceramic actuators and sensors. In comparison to conventional methods they provide the advantage to quantify the effect of new design features without the necessity to make the brake squeal. In this paper the investigation of phase shifts between characteristic dynamic state variables is examined more in detail. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The role of data transfer on the selection of a single vs. multiple mesh architecture for tightly coupled multiphysics applications

Data transfer from one mesh to another may be necessary in a number of situations including spatial adaptation, remeshing, arbitrary Lagrangian-Eulerian (ALE), and multiphysics simulation. Data transfer has the potential to introduce error into a simulation; the magnitude and impact of which depends on the application, transfer scenario, and the algorithm used to perform the data transfer. During a transient simulation, data transfer may occur many times, with the potential of error accumulation at each transfer. This paper examines data transfer error and its impact on a set of simple multiphysics problems. Data transfer error is examined using analytical functions to compare schemes based on interpolation, area-weighted averaging, and L² minimization. An example error analysis is performed to illustrate data transfer error and behavior for a simple problem. Data transfer error is also investigated for a one-dimensional time-dependent system of partial differential equations. This study concludes that data transfer error can be significant in coupled multiphysics systems. These numerical experiments suggest that error is a function of data transfer scheme, and characteristics of the field data and mesh. If there are significant differences in the meshes in a multiple mesh simulation, this study suggests that data transfer may lead to error and instability if care is not taken. Further, this work motivates that data transfer error should be included in the estimation of numerical error when data transfer is employed in a simulation.     

Modeling concept and numerical simulation of ultrasonic wave propagation in a moving fluid-structure domain based on a monolithic approach

In the present study, we propose a novel multiphysics model that merges two time-dependent problems – the Fluid-Structure Interaction (FSI) and the ultrasonic wave propagation in a fluid-structure domain with a one directional coupling from the FSI problem to the ultrasonic wave propagation problem. This model is referred to as the “eXtended fluid-structure interaction (eXFSI)” problem. This model comprises isothermal, incompressible Navier–Stokes equations with nonlinear elastodynamics using the Saint-Venant Kirchhoff solid model. The ultrasonic wave propagation problem comprises monolithically coupled acoustic and elastic wave equations. To ensure that the fluid and structure domains are conforming, we use the ALE technique. The solution principle for the coupled problem is to first solve the FSI problem and then to solve the wave propagation problem. Accordingly, the boundary conditions for the wave propagation problem are automatically adopted from the FSI problem at each time step. The overall problem is highly nonlinear, which is tackled via a Newton-like method. The model is verified using several alternative domain configurations. To ensure the credibility of the modeling approach, the numerical solution is contrasted against experimental data.     

Modeling of the Wear Particle Flow in Tribological Contacts

The dynamics of tribological systems with pronounced memory effects are characterized by the complex coupling of mechanical, thermal, and chemical processes. At the Institute of Dynamics and Vibrations in Braunschweig, Cellular Automata have been developed that facilitate the evaluation of dynamics in technically relevant systems within a reasonable time. The flow of wear material is decisive for the formation, localization, and reconstitution of load-bearing structures or films. In this paper, two opposed frictional contacts are chosen exemplarily for the investigation of the wear particle flow: a vehicle brake system and the sanding of wood. For this purpose, a modeling technique is proposed that is based on established force laws for micro particles and differentiates mechanisms of transport for different phases of the particle movement. The resulting transport of a single particle interacting with the topology of the frictional gap is analyzed for varying particle properties and process parameters. In a second step the insights are transferred to a set of rules for a Cellular Automaton which allows for quick evaluation and the incorporation of coupled effects. The validity and quality of the model transfer are discussed. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical Simulation of Surface Scanning in an Atomic Force Microscope Environment

In this contribution a model for the numerical simulation of an atomic force microscope (AFM) is presented. A challenge of this goal is the treatment of the multiphysics phenomena on the microscopic length-scale. Hence a coupled strategy is required to incorporate the different physically aspects and their interactions. The strategy is embedded in a nonlinear finite element formulation, where the different aspects are tackled by direct and weak coupling. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

车站咽喉通过能力可视化计算集成系统的研究

在对国内外咽喉道岔通过能力计算方法比较与分析基础上 ,论文提出了车站咽喉通过能力可视化计算集成系统的系统结构和功能设计 ,应用图论和网络优化技术对车站咽喉布置、咽喉及车站作业过程进行抽象建模 ,建立了咽喉作业占用安排网络优化和咽喉作业能力的复合递阶决策模型 .该研究综合运用上述模型、算法、计算机信息处理技术和图形技术 ,可视化模拟咽喉作业情况 ,实现了核心基础数据计算机模拟采集、作业优化安排和最大可实现能力的查定及优化 ,并将结果以图形方式输出 .通过实例验证表明 ,计算结果合理可信 ,可用于车站咽喉能力的评价检验 .     

Modelling of lateral oscillations in the interface of brake systems

The research of the dynamics in the boundary layer of brake pads can afford revealing technical expertise concerning different phenomena occurring in brake systems (e.g. squealing, judder, Hot Spots). For manufacturers of brake systems, the phenomenon “squealing” is of particular interest due to the desired driving comfort. The mentioned phenomena have been researched by numerous scientists. Different models have been developed and approved by experimental results. The authors agree upon the fact that the main excitation mechanism of the mentioned effects in brake systems is caused by the variation of the lateral (in-plane) friction force and friction torque respectively [1]. A model describing the dynamical interaction of friction and wear in the contact zone of brake systems has been introduced in [2]. Based on this theory, the brake pad's boundary layer consists of characteristic hard and smooth structures on the mesoscopic length scale. A new concept of the initiation of the squealing mechanism is based on the synchronisation mechanism of these so-called patches emerging from the dynamical interaction of the friction partners. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification and estimation of parameters defining a class of hybrid systems

In this paper, we consider the problem of parameter estimation in an air brake system. In an air brake system, the pressure of air in the brake chamber and the displacement of the pushrod and their derivatives form a set of states that characterize the system. The position of a valve or mass flow rate of air is an input and the pressure is the measured variable or the output. The pressure acting on the pushrod of the brake chamber causes motion, and the mode in which the system operates depends on the displacement of the pushrod. The mode-dependent nature of the system is a result of different sets of spring compliances associated with the piston in different ranges of its displacement. The mode to mode transition in the air brake system is governed by a parameter which is the clearance between the brake pads and the drum. The clearance between the brake pads and the drum can vary due to a variety of factors — for example, brake pad wear or brake fade. In these applications, characterizing the transition from one mode to another requires a lot of constitutive assumptions, and it can be difficult to calibrate the parameters associated with the constitutive assumptions. We therefore treat the air brake system as a system in which the parameter governing the transition from one mode to another (clearance between the brake pads and the drum) is not known exactly. Clearly, this parameter dictates the time delay and lag between the command and delivery of the brake torque at the wheels and affects the stopping distance of the vehicles considerably. The problem of identification considered in this paper is as follows. Suppose that the pressure of the fluid were to be measured and that the motion of the piston is not measured. Is it possible to estimate the final displacement of the piston without knowing the parameters that govern the system to transition from one mode to another?     

Study on numerical simulation methods of the railway vehicle-track dynamic interaction

A very efficient numerical simulation method of the railway vehicle–track dynamic interaction is described. When a vehicle runs at high speed on the railway track, contact forces between a wheel and a rail vary dynamically due to the profile irregularities existing on the surface of the rail. A large variation of contact forces causes undesired deteriorations of a track and its substructures. Therefore these dynamic contact forces are of main concern of the railway engineers. However it is very difficult to measure such dynamic contact forces directly. So it is important to develop an appropriate numerical simulation model and identify structural factors having a large influence on the variation of contact forces. When a contact force is expressed by the linearized Hertzian contact spring model, the equation of motions of the system is expressed as a second–order linear time–variant differential equation which has a time–dependent stiffness coefficient. Applying a well–known Newmark direct integration method, a numerical simulation is reduced to solving iteratively a time–variant, large–scale sparse, symmetric positive–definite linear system. In this study, by defining a special vector named a contact point one, it is shown that this time–variant stiffness coefficient can be expressed simply as a product of the contact point vector and its transpose and so the Sherman–Morrison–Woodbury formula applied for updating the inverse of the coefficient matrix. As a result, the execution of numerical simulation can be carried out very efficiently. A comparison of the computational time is given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A fast method for computing time-dependent normal pressure distributions with cellular automaton

When two bodies slide against each other, one part of the dissipated energy causes a topography change. Tribological research on brake bads shows a rich dynamic of the boundary layer: plateau-like structures of a typical length scale grow with time due to agglomerating wear particles and collapse spontaneously at a stability limit [4], [1]. This time-dependent behaviour can be modeled with cellular automata, which consider local resolution of temperature, wear particle density and frictional power [4]. Beside this the instationary normal pressure distribution and the distinction between areas with and without contact is expected to have a significant influence [3]. This paper derives a fast scheme to estimate the time-variant pressure distribution of a deterministic and dynamic topography by a cellular automaton. The approach is discussed in the light of computational performance and the solution's characteristics. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation and Analysis of Thermal Fatigue Based on Imperfection Model of Brake Discs

A non-linear FEM model of brake discs of high-speed trains with thermal-mechanical coupling has been established in ANSYS. The simulation and analysis of 3-D transient temperature field and stress field of brake discs have been carried out for the braking process. According to typical imperfections of brake discs, some imperfection models of brake discs have been developed and the thermal stresses of different models are obtained through simulation and analysis. By comparing results of different models, the influence of imperfection parameters, including the position, depth and size, is resulted for the thermal resistance of brake discs. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of direct chill casting under the influence of a low-frequency electromagnetic field

A comprehensive, multiphysics, meshless, numerical model is developed for the simulation of direct chill casting under the influence of a low-frequency electromagnetic field. The model uses mixture-continuum-mass, momentum and energy-conservation equations to simulate the solidification of axisymmetric aluminium-alloy billets. The electromagnetic-induction equation is coupled with the fluid flow and used to calculate the Lorentz force. The involved partial-differential equations are solved with the meshless-diffuse-approximate method by employing second-order polynomial shape functions and a 13-noded local support. An explicit time-stepping scheme is used. The boundary conditions for the heat transfer involve the effects of hot-top, mould chill and direct chill. The use of a meshless method and the automatic node-arrangement generation made it possible to investigate the complicated flow structures in geometrically complex inflow conditions, including sharp and curved edges, in a straightforward way. A time-dependent adaptive computational node arrangement is used to decrease the calculation time. The model is demonstrated by casting an Al-5.25wt%Cu aluminium alloy billet with a radius of 120 mm. Results on simplified and realistic inflow geometry are considered and compared. The effect of the low-frequency electromagnetic force on the temperature, liquid fraction and fluid flow are investigated under different current densities and frequencies.