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.     

Dynamic thermal behavior of a brake system

A mathematical model is presented to describe the thermal behavior of a brake system that consists of shoe and drum. The model is solved analytically using Green's function method for any type of the stopping braking action. In terms of the obtained solutions, the transient temperature distribution of the brake is described. The thermal behavior is investigated for three specified braking actions that are the impulse, unit step and trigonometric stopping actions.     

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.     

电厂锅炉锅筒寿命计算

从锅炉锅筒运行中产生疲劳寿命损耗的实际情况出发,给出锅炉锅筒寿命计算的方法及计算机框图,并作实例计算。     

增压锅炉汽包应力的有限元分析

对增压锅炉汽包在瞬态状态下所受到的工质的内压应力和热应力进行了分析,得出了增压锅炉汽包在瞬态状态下所受到内压应力和热应力随时间变化的规律以及汽包的应力集中部位,为增压锅炉汽包在瞬态工况下的安全运行,最优启动以及变负荷方案提供了理论依据。     

Initiation of Bulges in a Coke Drum Subjected to Cyclic Heating and Cooling,also Cyclic Mechanical Loads

Coke drums are equipments of an oil refinery system used to separate petroleum coke from lighter oils. During operations, a coke drum is subjected to cyclic heating and cooling also cyclic mechanical loads. Thus, the useful life of a coke drum is much shorter than the other equipments in the refinery. Bulges are commonly problems found in a coke drum. The initiation mechanisms of the bulges are not clear yet. However, there are two postulates have been proposed. First is that bulges are caused by contact stresses due to differential expansion between solid coke and steel. Second is that they are caused by thermal stresses due to presence of hot and cold spots in the coke drum wall. The present paper tends to agree with the second one. The main objective is to demonstrate that thermal stresses are sufficient to initiate the bulges. A coke drum with overall length, diameter, and thickness of 25.46 m, 6.4 m, and 42 mm, respectively has been taken into analysis. In order to provide actual temperature boundaries, operational temperatures of the coke drum have been measured and collected while it is operating. A cycle which shows the most severe operational temperature has been selected to be analyzed. Two-dimensional axisymmetric model was developed and stresses analysis upon the model was carried out by using ANSYS FEM commercial code. The equivalent stresses and the yield strength as a function of time are plotted. The results show that the maximum equivalent stress can reach the yield strength of the coke drum material. This concludes that the bulges are mainly initiated by thermal stresses.     

300MW机组锅炉汽包寿命在线监测系统的研究

采用三维有限元理论,对300MW机组锅炉汽包在内压作用下的应力场进行了分析,所得到的理论应力集中系数比TDR301的推荐值大17.3％,并用热弹性理论计算准稳态下汽包的热应力。在此基础上对TRD301给出的疲劳寿命计算方法提出了改进建议,开发了一套300MW机组锅炉汽包寿命在线监测系统。该系统利用计算机、智能化数据采集和通信转换对锅炉汽包运行全过程实行温度、压力和寿命的管理。经在某电厂1021t/h锅炉上运行,效果良好。达到了对锅炉汽包寿命进行在线监测和指导锅炉运行的目的。     

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.     

TRANSIENT THERMAL STRESS ANALYSIS AND BENDING BEHAVIOR OF AN ANGLE-PLY LAMINATED SLAB

Abstract

This paper is concerned with a theoretical treatment of thermal stress and bending behavior in a transient state of a multilayered, nonisotropic, laminated slab. As an analytical model, we consider an infinitely long, laminated slab, which consists of obliquely directed layers with orthotropic material properties; the model corresponds to the so-called angle-ply laminate. We solve the thermoelastic problem for the slab under the condition of uniformly distributed heat supply from its one surface. Introducing a method of Laplace transforms to the temperature field, we obtain the temperature solution using the residue theorem, and we evaluate the thermal stresses in a transient state by using the elementary plate theory. As an example, we carry out numerical calculations for the five-layered angle-ply laminate, evaluate the thermal stress distributions and the bending behavior, and examine the influence of the ply angle on the thermal stress distribution.     

Thermal stress analysis of eccentric tube receiver using concentrated solar radiation

In the parabolic trough concentrator with tube receiver system, the heat transfer fluid flowing through the tube receiver can induce high thermal stress and deflection. In this study, the eccentric tube receiver is introduced with the aim to reduce the thermal stresses of tube receiver. The ray-thermal-structural sequential coupled numerical analyses are adopted to obtain the concentrated heat flux distributions, temperature distributions and thermal stress fields of both the eccentric and concentric tube receivers. During the sequential coupled numerical analyses, the concentrated heat flux distribution on the bottom half periphery of tube receiver is obtained by Monte-Carlo ray tracing method, and the fitting function method is introduced for the calculated heat flux distribution transformation from the Monte-Carlo ray tracing model to the CFD analysis model. The temperature distributions and thermal stress fields are obtained by the CFD and FEA analyses, respectively. The effects of eccentricity and oriented angle variation on the thermal stresses of eccentric tube receiver are also investigated. It is recommended to adopt the eccentric tube receiver with optimum eccentricity and 90° oriented angle as tube receiver for the parabolic trough concentrator system to reduce the thermal stresses.     

Transient Response of Thermoelastic Hollow Sphere Under Thermal Shocks

The thermoelastotransient response in a hollow sphere under different thermal shocks is analyzed. Coupled thermal stress and non-Fourier heat conduction are considered in the mathematic model. The systems of heat and motion equations are successfully uncoupled before Laplace transformation, and an analytic solution is given. By means of numerical Laplace inversion, the temperature and stress distributions are presented. From the numerical results from different thermal shocks, the influence of the impact speed to the coupled thermal stress problems can be observed. A comparison of temperature and stress distribution is given between the coupled thermal stress problems and static thermoelastic problems.     

基于雨流计数法的锅炉汽包寿命实时监测

建立了汽包温度场、应力场监测模型,基于从电厂DCS(分布控制系统)中取出的锅炉汽包启动数据,通过有限元分析确定汽包的危险点,并修正了该点的应力集中系数,给出了汽包瞬态温度场计算的隐式差分方法和危险点的当量应力计算公式,改进了雨流计数方法,提出了采用应力稳定原则作为判定汽包启停状态结束的准则,统计每次启停过程中不同应力幅的循环次数,并据此确定汽包的寿命损耗。通过对锅炉汽包一次冷启动数据分析,验证了本文方法的有效性,研制了锅炉汽包寿命实时监测系统,经600 MW机组锅炉汽包的监测运行表明,效果良好,达到了对锅炉汽包寿命损耗进行实时监测并指导运行的目的。     

基于汽包寿命的1 021 t/h锅炉启动过程的优化研究

1引言300 MW机组已经成为我国火力发电的主要机组。随着用电结构的变化,电网负荷的峰谷差日益增大,许多大容量机组已参予调峰运行。机组在调峰过程中,锅炉启停、变负荷运行使汽包受到交变应力作用,产生低周疲劳损伤。随着机组启停次数的增加,汽包疲劳损伤加剧,给电力生产留下安     

Fourier finite element model for prediction of thermal buckling in disc clutches and brakes

Numerical analyses are performed on thermal buckling of annular rings using a reduced Fourier method. The stress stiffness matrix is derived from the geometric nonlinearity in the Green strains with a predefined circumferential wave number. The method is first validated through the commercial software Abaqus using an axisymmetric model. It is then implemented to solve more general nonaxisymmetric problems with multiple waves along thecircumference. It is shown that there exists a particular wave number with which the buckling temperature reaches a minimum. This research has potential applications in automotive clutch and brake designs against thermal buckling.     

Analysis of thermal stress evolution in the steam drum during start-up of a heat recovery steam generator

A program to predict the transient characteristics of the heat recovery steam generator (HRSG) is constructed and the start-up behavior of the high-pressure part of an HRSG is analyzed with a special focus on the estimation of the thermal stress in the steam drum. Three HRSG start-up procedures (steady gas turbine without gas bypass, steady gas turbine with gas bypass, start-up gas turbine) are simulated. The gas bypass is conducted during the initial stage of the start-up. Estimation of the maximum thermal stress makes it possible to optimize the gas bypass mode. It is shown that bypassing part of the gas flow lowers the peak stress much in case of the steady gas turbine exhaust condition. Examples of the scheduling of the gas flow increase using the step and ramp modes are demonstrated. In case of the simultaneous start-up, the peak stress is considerably low due to the gradual increase of gas temperature and mass flow and bypassing just a small portion of gas flow is enough to keep it under the allowable limit.     

Effect of thermal stress on crack growth in inhomogeneous cylindrical superconductor

The effect of thermal stress on the growth of central cracks in inhomogeneous cylindrical superconductors is investigated assuming that the material properties vary linearly with the radial coordinate and temperature differences. General expressions for the temperature distribution and thermal stress in terms of a Bessel equation and the plane strain approach are derived. The results indicate that the distributions and variations in the radial and hoop thermal stresses in an inhomogeneous superconductor differ from those in homogeneous superconductors. However, thermal stress affects the crack growth similarly in both superconductor types. The thermal-stress analysis should be useful for the crack growth prediction regarding inhomogeneous superconductors.     

Numerical study of thermal stresses in high-temperature proton exchange membrane fuel cell (HT-PEMFC)

The purpose of this work is to numerically examine the thermal stress distributions in a high-temperature proton exchange membrane fuel cell (HT-PEMFC) based on a phosphoric acid doped polybenzimidazole (PBI) membrane. A fluid structure interaction (FSI) method is adopted to simulate the expansion/compression that arises in various components of a membrane electrode assembly (MEA) during the HT-PEMFC assembly processes, as well as during cell operations. First, three-dimensional (3-D) finite element method (FEM) simulations are conducted to predict the cell deformation during cell clamping. Then, a nonisothermal computational fluid dynamic (CFD)-based HT-PEMFC model developed in a previous study [1] is applied to the deformed cell geometry to estimate the key species and temperature distributions inside the cell. Finally, the temperature distributions obtained from these CFD simulations are employed as the input load for 3-D FEM simulations. The present numerical study provides a fundamental understanding of the stress–temperature interaction during HT-PEMFC operations and demonstrates that the coupled FEM/CFD HT-PEMFC model presented in this paper can be used as a useful tool for optimizing HT-PEMFC clamping and operating conditions.     

Thermo-mechanical stress analyses of solid oxide fuel cell anode based on three-dimensional microstructure reconstruction

During high-temperature operation of a solid oxide fuel cell, the stresses caused by mismatch of thermal expansion coefficients between different materials and external mechanical loads may cause the rising of damage risk of nickel-yttria-stabilized zirconia anode. It is quite difficult to quantify the mechanical characteristics of a composite anode without investigating on the stress distribution in its real microstructure. However, the high operating temperature and extremely complex microstructure in micro-scale determine the high difficulty in in-situ measurement of thermo-mechanical stress distribution. In this work, the microstructures of six different anode samples, fabricated by using identical nickel oxide-yttria-stabilized zirconia powder mixture, are reconstructed in three-dimension based on the dual-beam focused-ion-beam-scanning-electron-microscopy. The three-dimensional thermo-mechanical stress distributions of different microstructures are conducted at operating temperature based on the finite element method. The effects of both thermal expansion coefficients mismatch between nickel and yttria-stabilized zirconia and external mechanical loads are analyzed. The mechanical failure probabilities of yttria-stabilized zirconia phase in different reconstructions are estimated based on the obtained stress distributions to investigate the influence of microstructure characterizations on nickel-yttria-stabilized zirconia anode strength.     

Material design of a film cooling system using experimental heat transfer data

The present study numerically calculates the temperature and thermal stress distributions near a normal cooling hole. We evaluate the effects of material properties on thermal damage by using local heat transfer data from previous experiments. The experimental results are converted into the surface’s heat transfer coefficients and the adiabatic wall temperature while using surface boundary conditions. The calculated results reveal that the thermal stresses depend on the main stream temperature and the material properties. To predict the maximum thermal stress near the normal cooling hole, we provide a single correlation consisting of the material properties and the main stream temperature.     

A thermoelastic spherical shell with and without energy dissipation

In this work, we apply the Green and Naghdi generalized thermoelasticity theory to a one-dimensional problem of distribution of thermal stresses and temperature in a generalized thermoelastic medium in the form of a spherical shell subjected to sudden change in the temperature of its external boundary. The results are compared to the generalized thermoelasticity theory with one relaxation time. Numerical results are computed and represented graphically for temperature, displacement, and stress distributions.