3D investigation of thermal stresses in a locomotive ventilated brake disc based on a conjugate thermo-fluid coupling boundary conditions

The frictional heat generated during braking application can cause several negative effects on the brake system such as brake fade, premature wear, thermal cracks and disk thickness variation. It is then important to determine with precision, the temperature field and thermal stresses of the brake disc. In this study, thermal stress analyses on a ventilated locomotive wheel-mounted brake disc R920K with a three-dimensional model for two cases (the first case considers braking to a standstill; the second case considers braking on a hill and maintaining a constant speed) were investigated. The rate of braking heat generation is calculated using the assumption of uniform pressure distribution at the contact area. Then, thermal stress analyses for each case were performed. Finally, we have found that the maximum thermal stresses occur in the case with an emergency braking in the beginning of the braking process.     

A thermomechanical model for the analysis of disc brake using the finite element method in frictional contact

Abstract

In this work, a numerical simulation of the transient thermal analysis and the static structural one was performed here sequentially, with the coupled thermo-structural method using the ANSYS software. Numerical procedure of calculation relies on important steps such that the CFD thermal analysis has been well illustrated in 3D, showing the effects of heat distribution over the brake disc. This CFD analysis helped in the calculation of the values of the thermal coefficients (h) that have been exploited in the 3D transient evolution of the brake disc temperatures. Three different brake disc materials were selected in this simulation and comparative analysis of the results was conducted in order, to derive the one with the best thermal behavior. Finally, the resolution of the coupled thermomechanical model allows to visualize other important results of this research such as; the deformations, and the equivalent stresses of Von Mises of the disc, as well as the contact pressure of the brake pads. Following our analysis and results we draw from it, we derive several conclusions. The choice makes it possible to deliver the best brake rotor so as to ensure and guarantee the good braking performance of the vehicles.     

风电机组偏航制动器制动稳定性分析

针对风电机组偏航制动器制动不稳定问题，基于ABAQUS软件开展偏航制动器制动稳定性分析。运用复特征值分析法和不稳定倾向系数TOI值，分析制动压力、摩擦系数、偏航速度、弹性模量以及开槽方式等对制动稳定性的影响。基于全因子试验及Design-expert软件建立不稳定倾向系数TOI值响应面模型，并开展相关参数优化。研究表明：对制动稳定性具有显著影响的因素是摩擦系数、偏航制动缸弹性模量、摩擦片弹性模量；开双槽的摩擦片对制动稳定性影响显著，开单槽影响较小；制动稳定性受制动压力与偏航速度影响很小；参数优化后的偏航制动器制动不稳定系数降低73.7%。该研究结论可为偏航制动器设计、开发提供理论指导。     

THERMOELASTO-PLASTIC STRESSES AND THERMAL DISTORTIONS IN A BRAKE DRUM

Most analyses of thermal stresses generated in a brake drum are studies within either an elastic or a plastic region with constant yield strength. As a matter of fact, however, a severe brake application will create a thermal environment on the friction surface with an excessively high surface temperature. At a high temperature, the degradation of yield strength of a drum material may become significant and an important factor to be taken into account in the analysis. This article deals with the thermoelasto-plastic stresses and the thermal distortions produced in a brake drum during a severe braking condition, taking account of the temperature dependence of the yield strength of a drum material. It is found that high compressive thermoelastoplastic stresses are created during a brake application but eventually residual tensile stresses are developed in the vicinity of the rubbing surface in the course of cooling. These residual tensile stresses are strongly presumed to be one of the significant factors causing the heat crack in a brake drum. In addition, the thermal distortions of the drum suggest a loss of the contact area between the drum fictional surface and the brake shoe linings during braking.     

Three-dimensional transient temperature field of brake shoe during hoist’s emergency braking

In order to exactly master the change rules of brake shoe’s temperature field during hoist’s emergency braking, the theoretical model of three-dimensional (3-D) transient temperature field was established according to the theory of heat conduction, the law of energy transformation and distribution, and the operating condition of mining hoist’s emergency braking. An analytic solution of temperature field was deduced by adopting integral-transform method. Furthermore, simulation experiments of temperature field were carried out and the variation regularities of temperature field and internal temperature gradient were obtained. At the same time, by simulating hoist’s emergency braking condition, the experiments for measuring brake shoe’s temperature were also conducted. It is found, by comparing simulation results with experimental data, that the 3-D transient temperature field model of brake shoe is valid and practical, and analytic solution solved by integral-transform method is correct.     

Temperature in the railway disc brake at a repetitive short-term mode of braking

The finite element (FE) model to determine the transient temperature field in the ventilated disc brake of the traction diesel multiple unit (DMU) has been proposed. The advantage of the developed numerical model is the representation of mutual motion of the stationary pad and the rotating disc, by a heat source of arbitrary shape moving over the stationary disc. Computations were carried out for the pad and the disc separately introducing the heat partition ratio. Both the single and the multiple modes of braking were examined. The calculated distributions in contact temperature were compared with the corresponding results obtained from analytical solutions of the boundary-value thermal problem of friction, and with experimental data determined by the method of thermocouples. It was demonstrated that the calculated mean temperature on the friction surfaces of the brake components and the bulk temperature of the disc during multiple brake application agree well with the corresponding results, obtained by methods mentioned above.     

Thermal analysis of a novel retarder by using the nanofluid cooling system: Numerical and experimental approaches

To solve the problem of braking torque decline or even brake failure of vehicle retarders caused by high temperature due to long-time or high-power braking, the nanofluid with high thermal conductivity is introduced into the previously proposed novel retarder. To evaluate the nanofluid cooling capabilities, a model depicting the vertical fluid flow in the retarder is formulated. Adopting similarity transformations and a shooting method coupled with Runge–Kutta iterative technology, the model boundary value problem is tackled numerically. The cooling capabilities of three typical ethylene glycol (EG)-based nanofluids: Cu–EG, Al₂O₃–EG, and TiO₂–EG are investigated and compared. Finally, an experimental test is carried out to examine the temperature rise and the variation of braking torque for the retarder. It is demonstrated that Al₂O₃–EG nanofluid has the highest Nusselt number (rate of heat transfer), and more importantly, the braking torque of the proposed retarder decreases by only 8.2% under high-power braking condition.     

Temperature in thermally nonlinear pad–disk brake system

The influence of the thermal sensitivity of pad and disk materials on temperature at braking is under investigation. A mathematical model of process of frictional heating in a pad–disk brake system, which takes into account the temperature-sensitive materials, is proposed. The basic element of this model is the thermal problem of friction—a one-dimensional boundary-value heat conduction problem with temperature-dependent thermal conductivity and specific heat. Contrary to the prior studies of authors, where a simple nonlinearity was considered, in this article the arbitrary nonlinearity of the thermophysical properties of materials is studied. The solution of a nonlinear boundary-value heat conduction problem is obtained by the method of successive approximations. The numerical analysis of temperature is executed for some materials of a pad and a disk with and without taking into account their thermal sensitivity.     

GK型机车基础制动形式选择的探讨

通过对GK型机车两种制动形式的比较,对单、双侧制动的制动能力得出正确的结论,并对两种制动的优劣作出评述。认为:单侧制动方式能够很好地解决机车的闸瓦偏磨问题;如果采用合成闸瓦,则双侧制动时的制动力明显大于单侧制动时的制动力。     

Fatigue Analysis of Railway Wheels Under Combined Thermal and Mechanical Loads

Nowadays, the railway vehicles are widely used in many countries as one of the most important transportation systems. Nucleation and growth of fatigue cracks in railway wheels stem from different factors such as wheel-rail rolling contact, thermal loads between wheel-rail and wheel-brake block created in braking process, presence of structural defects in wheel material, and so forth. Also, increasing speed and axle loads of wheels aggravates these factors. These cracks can reduce wheel life and even in severe cases derailment may occur. Therefore, the thermo-mechanical fatigue problem of wheels is a very important issue as is doing an accurate mechanical and thermal analysis of the investigation and estimation of fatigue life of wheels, and also, the prediction of crack behavior under thermo-mechanical loads is necessary. In this article, stress fields created by combined thermal and mechanical loads in railway wheels is investigated. Thermal stresses are usually created as a result of frictional heating produced by applying brake shoes on the wheel tread and also as a result of the occurrence of slip between wheel and rail at the braking stage. The obtained results confirm the important effects of thermal loads on stress fields and fatigue life of wheels. In this article, thermal loads are determined by modeling the contact of the rail-wheel and two brake blocks and by identifying heat partition factors and friction coefficient between these components. One of the other advantages of the presented work is modeling of wheel rotation, while in many of the similar investigations either this rolling is not modeled or its effect is simplified as translating pressure distribution along the rail-wheel contact region. The use of a 3D FE analysis for determination of rail-wheel contact pressure instead of Hertz contact theory is also noteworthy.     

3D FE model of frictional heating and wear with a mutual influence of the sliding velocity and temperature in a disc brake

Numerical simulation of frictional heating in a disc brake of a typical passenger vehicle based on the equation of motion and the boundary-value problem of heat conduction was carried out. An influence of temperature-dependent coefficient of friction on the sliding velocity, braking time, braking distance and the thermomechanical wear was studied. Two materials of the pad combined with the cast-iron brake disc were examined. The dependencies of the coefficient of friction and wear rate on the temperature and contact pressure were derived from experimental measurements and implemented to the computational model of the brake. Comparisons of temperature for validation purposes calculated using the contact model developed in this study were made with the model introducing an approach based on the heat partition adopted from other studies.     

Measurements of brake disc surface temperature and emissivity by two-color pyrometry

A fiber optic two-color pyrometer was developed for brake disc surface temperature and emissivity measurements. The two-color pyrometer consists of a fluoride glass optical fiber, two HgCdTe detectors equipped with bandwidth filters and a data conditioning and acquisition device. The two-color pyrometer measures the brake disc temperature in the 200–800 °C range with a time resolution of 8 μs. The calibration formula for the signals obtained using a blackbody of known temperature is used to compute the true temperature. The uncertainty estimation for temperature and emissivity was obtained from the calibration results. Tests were carried out on known temperature target and a good correlation was found between results obtained with our two-color pyrometer and those obtained with a commercial two-color pyrometer. Hold braking and deceleration braking tests performed on a braking test bench enabled us to reach the brake disc surface temperature and emissivity during braking. Experimental results show a significant variation of emissivity during braking. Direct measurement of emissivity was carried out on the brake disc after braking and shows the emissivity dependence with the surface quality.     

Regenerative braking energy recovery strategy based on Pontryagin's minimum principle for fell cell/supercapacitor hybrid locomotive

A regenerative braking energy recovery strategy based on pontryagin's minimum principle (PMP) for Fuel Cell (FC)/Supercapacitor (SC) hybrid power locomotive was proposed in this paper. In the proposed strategy, the dynamic coefficient λ is used in PMP during the traction state of the locomotive, which makes system transient hydrogen consumption minimum. What's more, during locomotives brake state, according to the known parameters of SCs and operation indicators, an optimized braking speed curve can also be obtained which has maximum brake recovery rate. The results are obtained from RT-LAB platform testify that the proposed strategy is able to maximize SC absorption braking energy, and the energy recovery rate improves and maintains SC state of charge (SoC) in a reasonable and safe range, and decreases brake resistors energy consumption in the braking process.     

原东德EDK300/2型60t铁路起重机制动系统改造设计

简要介绍了原东德EDK300/2型60 t铁路起重机空气制动系统和基础制动装置等,研制出一种适合于铁路起重机的制动系统。对其改造方案、具体结构和计算分析进行了阐述。经改造后的制动系统能够满足运营要求。     

矿用提升机盘形制动器制动安全分析

通过解析矿用提升机制动器制动的工作原理,分析影响安全制动的因素,可以在工作中尽快找出影响安全制动的原因,并采用相应的解决方法使提升机在有效制动范围内运行。     

柴油机排气制动控制策略研究

介绍了DEUTZTCD2015柴油机排气制动与脚踏板优先级关系、排气制动起作用转速的控制策略,并通过试验进行验证分析：试验结果表明,TCD2015V06柴油机排气制动功能设计合理。     

A compromise solution for energy recovery in vehicle braking

A combined regenerative-dissipative brake system for a city bus is considered. The regenerative component consists of a fixed displacement hydraulic pump/motor discharging into or receiving high pressure fluid from a hydropneumatic accumulator. The braking force provided by the pump is determined by the pressure in the accumulator. It is brought into action only when a greater total braking force is required, in which case the conventional dissipative brake provides the difference. From a preliminary analysis using probability data for acceleration, an estimated 45% of the total kinetic energy absorbed in braking could be channeled through the hydropneumatic component. The system was conceived as a practical alternative to a more costly fully regenerative system employing a variable displacement pump.     

列车制动技术的研究与展望

概述了列车常用的几种制动方式,分析了其工作原理、特点和应用场合。针对应用最广泛的闸瓦制动方式和盘形制动方式,重点阐述了提升其制动性能的方法及应用。通过分析闸瓦工作状况对列车行车安全的影响,讨论了闸瓦自动检测技术的重要性和研究现状。最后对列车制动技术的发展做了展望。     

机车制动安全系统的研究与探讨

机车运行中制动系统本身出现故障不能正常工作时,往往会造成机破。以装用JZ-7型制动机的机车为例,探讨安装机车制动安全系统确保机车有效制动和安全运行。     

Axisymmetric FEA of temperature in a pad/disc brake system at temperature-dependent coefficients of friction and wear

Robust braking results in heat generation whose effects may have considerable impact on the parameters of the process such as wear rate and coefficient of friction. Fluctuations of the latter disagree with essential operational and braking requirements. Finite element analysis (FEA) of a single braking process for axisymmetric heat conduction problem of friction in a pad/disc brake system in the present article was carried out. Two materials of the pad FC-16L (retinax A) and FMC-11 (metal ceramic) and one material of the disc ChNMKh (cast iron) were analysed. Experimental dependencies of the coefficient of friction and wear rate on the temperature under specified contact pressures for these two friction pairs were approximated and applied to FE contact model. The temperature and wear evolutions on the contact surface of the pad/disc brake system obtained for constant and temperature-dependent abovementioned coefficients were confronted and compared. Mutual correlations of the obtained results with the studied materials were discussed.