600MW超临界锅炉膜式水冷壁的热应力分析

建立了超临界锅炉膜式水冷壁的热应力场有限元计算模型。结果表明,鳍片限制管壁变形从而在接触面产生热应力,最大热应力值为1.301 GPa,而在水冷壁管的向火侧可自由膨胀导致此处的热变形最大,最大变形量为0.306mm;水冷壁最大热应力随管壁厚度的增大而增大,而随鳍片厚度的增大反而减小,厚度每增加1mm,最大热应力变化量分别为30MPa和40MPa,水垢厚度对水冷壁最大热应力的影响较小。     

纳米陶瓷涂层对ω型活塞的热结构影响北大核心CSCD

研究了热障涂层厚度对活塞温度、热应力及热变形分布的影响,结合硬度塞法测试无涂层活塞特征点的温度值,采用有限元法与涂层活塞仿真结果进行比较。对不同厚度的涂层进行温度和热应力分析。研究结果表明,在涂层厚度0.3 mm~0.6 mm范围内,厚度每增加0.1 mm,活塞顶面温度提高10℃~17℃,活塞基体温度下降19℃~27℃。与无涂层活塞相比,0.6 mm厚的涂层活塞基体温度最大降幅为10.8%。涂层表面的热应力随着涂层厚度的增加而减小,涂层活塞基体的热应力变化不大。最大热变形处在陶瓷涂层,最大热变形量在活塞与气缸套允许范围之内。     

固体电热储能系统热变形分析与结构优化研究

为了解决固体蓄热装置中蓄热模块在温度载荷下容易发生热变形,导致蓄热体结构不稳定甚至坍塌问题,采用弹性力学理论对温度载荷下蓄热体的热变形量及热应力进行理论推导,利用数值模拟方法分析了不同占孔比、不同进口空气温度以及固定约束对蓄热体热变形及温度分布的影响,并搭建试验平台对数值模拟结果进行验证。研究表明:进口空气温度越高,蓄热体热变形越大,进口空气温度为950℃时最大变形率达到1.73%;相同工况下,20%占孔比蓄热体热变形量最小、温度分布均匀;固定约束位置出现热应力集中现象,最大热变形出现在蓄热体顶部。     

形状记忆可展桁架在轨热变形分析研究

本文借助I-DEAS软件建立了针对形状记忆可展桁架的热-结构耦合分析模型,并试验验证了分析模型的准确性。在此基础上,采用多层隔热复合材料作为热控措施,计算分析有/无热控措施及预紧力大小对桁架温度与热变形的影响。结果表明,包覆多层隔热材料效果明显,可将桁架在轨周期内的温度差减小85%,位移差减小80%,有利于对可展桁架进行温控,实现展开与收拢,减小运行期间振动的影响。桁架变形大小由预紧力和热应力共同决定,随着预紧力增大,桁架位移差逐渐减小。     

汽轮机供热改造后导汽管变形的数值研究

国内许多电厂将纯凝式汽轮机改造为供热式汽轮机,在中低压缸导汽管上打孔安装抽汽管道的改造方法最为普遍,但改造后低压缸出现了漏汽现象,从而导致汽轮机的热效率降低。利用有限元分析软件对汽轮机供热改造前后的中低压缸导汽管进行了热变形和热应力分析,结果表明供热改造后导汽管的热变形和热应力都明显增加。为此,对导汽管进行了优化设计,增加了波纹节的冷拉值,并对优化设计后的导汽管再进行有限元分析。分析结果显示优化设计后导汽管在最大抽汽工况下热变形和热应力大大减少,此结果也为今后汽轮机的供热改造提供了理论依据。     

排气歧管热应力模拟计算及缸盖边界条件影响的分析

针对某型号柴油机在热冲击试验过程中排气歧管出现裂纹的问题,利用软件仿真技术进行了排气歧管的热应力模拟计算,分析了产生裂纹的原因。探讨了缸盖建模方法及缸盖设定温度对排气歧管热应力计算的影响。计算结果表明,缸盖限制了排气歧管的自由变形,在排气歧管裂纹出现部位产生较大的应力;在发动机冷热冲击试验时,排气歧管温度的变化造成热应力随之发生变化,导致排气歧管因热疲劳产生裂纹失效;采用简化的缸盖模型与完整缸盖模型所得的排气歧管热应力分布趋势一致,可用于排气歧管的热应力计算。     

30/38柴油机活塞热力耦合有限元分析研究

采用有限元软件ANSYS,分析了30/38柴油机活塞的温度场、热应力及热变形;并通过热-机耦合的方法,分析了该机活塞的耦合应力场。研究结果表明:活塞顶部应力以热应力为主,温度对活塞的应力和变形起主导作用。在此基础上提出了有关活塞的研制建议。     

不同载荷对柴油机缸套变形的影响研究

建立了缸体、缸盖、缸套等部件的四缸柴油机装配耦合模型,在加载热负荷的基础上分析了热应力、螺栓预紧力、缸内最高燃烧压力及活塞侧击力对缸套变形的影响。研究结果表明:在各加载方案中,缸套膨胀和压缩变形均表现为1#缸、4#缸缸套变形较大,2#缸、3#缸缸套变形较小;不同加载方案的缸套变形规律相似,缸套热应力产生的热变形占主导地位;在加载热负荷的基础上,螺栓预紧力、缸内最高燃烧压力对缸套综合变形最大值影响较大,而活塞侧击力对缸套综合变形最大值影响较小;活塞侧击力对缸套径向变形最大值的分布区域影响较大,但对机体与缸套主应力及变形值影响较小。     

高强度柴油机活塞温度与应力场有限元分析及其结构改进

结合柴油机活塞发展现状,针对某型号高强度柴油机,利用SolidWorks建立该柴油机活塞的三维模型,并用ANSYS对活塞进行有限元分析,讨论活塞在高温环境、最高燃烧压力或最大侧向力作用下的温度场、应力分布和变形情况。分析结果表明,活塞主要承受热应力和热变形,最大耦合应力在油道顶部,约270MPa,最大变形出现在活塞顶部边缘,变形量约0.08%,变形随活塞高度降低而减小,在裙部略有上升。活塞头部在销孔方向上热变形大于耦合变形,两者差值随活塞头部高度降低而减小。活塞在垂直于销孔轴线方向上的耦合变形总体上大于平行于销孔方向的耦合变形。同时,燃烧室喉口、环槽和销座处应力集中明显,针对上述薄弱区域进行结构改进,发现改进后应力值均显著降低,这些结构改进对高强度柴油机活塞设计开发具有重要指导意义。     

基于ABAQUS软件的CB250汽油机活塞热分析

活塞作为内燃机的主要受热零部件之一,由于受热面积大,散热条件差,承受非常大的热负荷。在进行设计改进时,需考虑其热负荷问题,应对其进行热场预测及数值分析,研究其热应力和热变形。笔者运用有限元分析软件Hypermesh和Abaqus,仿真分析得到活塞三维温度场,并计算其热变形,为活塞的结构改进和优化提供了重要依据。     

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.     

THERMAL STRESSES IN FUNCTIONALLY GRADED MATERIALS

The thermal stress problems of functionally graded materials (FGMs), as one of the advanced high-temperature materials capable of withstanding the extreme temperature environments, are discussed. The FGMs consist of the continuously changing composi tion of two different materials. For example, one is an engineering ceramic to resist the severe thermal loading from the high-temperature environment, and the other is a light metal to maintain the structural rigidity. When the FGMs are subjected to extremely severe thermal loading, large thermal stresses are produced in the FGMs. Therefore, one of the most important problems of FGMs is how to decrease thermal stresses and how to increase heat resistance. The optimal composition profile problems of the FGMs in decreasing thermal stresses are discussed in detail. When FGMs are subjected to extremely severe thermal loading, the FGMs are damaged. The crack initiates on the ceramic surface and propagates in the FGMs. It is important to discuss the thermal stresses in the FGMs with various types of cracks. The thermal stress intensity factors in the FGMs with various types of crack are treated analytically and numerically. The optimal composition profile problems of the FGMs in decreasing thermal stress intensity factor are studied. Finally, the crack propagation paths due to thermal shock are discussed.     

THERMAL STRESSES INTENSITY FACTOR FOR FUNCTIONALLY GRADIENT PLATE WITH AN EDGE CRACK

Thermal stress problems of a functionally gradient plate as one of the advanced high-temperature materials capable of withstanding the extreme temperature environments, with and without an edge crack, are discussed One of the most important problems of the thermal stress in the functionally gradient plate with the crack are how to decrease the thermal stress intensity factor and how to determine the optimally continuous profile of the composition of the plate. The functionally gradient plate is subjected to a cycle of heating and cooling on the ceramics surface of the plate. The material properties of the functionally gradient plate are dependent on the temperature and the position. The optimally continuous profile of the composition of the plate is discussed. The numerical results for thermal stresses and the thermal stress intensity factor are shown for many temperature conditions and for many continuous profiles of the composition of the plate.     

UNSTEADY THERMAL STRESS ANALYSIS IN AXISYMMETRIC PROBLEMS BY MEANS OF BOUNDARY ELEMENT METHOD

The boundary integral formulation for unsteady thermal stresses in axisymmetric quasi-static problems is proposed. It is shown that axisymmetric unsteady thermal stress problems can be easily solved without the volume integral by means of the thermoelastic displacement potential and boundary element method. It is also shown that the time integral can be easily carried out analytically. In order to investigate the accuracy of rhis method, unsteady thermal stress distributions for a hollow circular cylinder and a torus are obtained.     

水电站厂房底板施工期及运行期温度应力场仿真分析

水电站厂房底板是大体积混凝土浇筑块,其温度应力比较大。本文针对某水电站厂房结构复杂,混凝土分块、跳仓浇筑,错位搭接的难题,提出了将ANSYS有限元计算软件与西安理工大学开发的温度应力仿真计算程序以及Surfer绘图软件三者相结合的方法,合理地解决了仿真计算中的难题,从而比较真实准确地分析了厂房底板的温度应力场。     

GROWTH INSTABILITY DURING PLANAR SOLIDIFICATION WITH A MOLD OF FINITE THERMAL CAPACITY

The temperature and the stress fields in the solidified layer and in the mold of finite thickness for a unidirectional casting process are investigated. Earlier solutions are extended to include the effect of the thermal capacity of the mold on the freezing front growth instability. A numerical solution is obtained for both the heat conduction and the residual stress problem. The results show that the perturbation in contact pressure tends asymptotically to a maximum value at larger times for the lower values of the thermal capacities of the mold materials. The magnitude of the contact pressure perturbation is decreased by the inclusion of the thermal capacity of the mold material, and this effect is enhanced for less distortive and thicker molds. The present article assumes that the thermal and mechanical problems are uncoupled along the casting mold interface. Despite this limitation, the results presented in this article indicate that a mold with a higher thermal capacity (or lower thermal diffusivity) might be less susceptible to thermoelastic instabilities associated with the contact pressure and its dependence on the thermal contact resistance at the casting mold interface.     

APPLICATION OF AN ALTERNATING METHOD TO THE THERMOELASTIC PROBLEMS WITH MULTIPLE CIRCULAR HOLES IN AN INFINITE DOMAIN

This paper presents a new efficient procedure to analyze the thermoelastic problems with multiple circular holes in two-dimensional infinite domain using an alternating method. To achieve this purpose, the analytical solutions including the temperature and associated thermal stress for the arbitrary heat flux across the single circular hole boundary in an infinite domain are first derived. Both the temperature and thermal stress fields in the thermal problems are simultaneously solved by these analytical solutions with the successive iterative superposition process. Compared with the solution of the conventional finite-element technique, the present method has been more accurate and has more advantages. Effects of the distributions and sizes of the holes on the stress concentration in the thermal problems also are evaluated in detail herein.     

CONTROL OF THERMAL STRESS AND STRAIN

The problem of assigning a prescribed thermal stress distribution in a structural part during its thermoelastic deformation is discussed in the first part. The theorem comprising the necessary and sufficient conditions for producing such a prescribed thermal stress distribution is formulated. An objective function is introduced to solve the simple problem of uniaxial stress states in rods. In general, such a function puts the posed problem into the class of optimization problems of the mechanics of deformable solids. Illustrative examples are explicitly solved. The problem of assigning a prescribed thermal strain distribution in a structural part during its thermoelastic deformation is briefly discussed in the second part. A direct approach for its solution is proposed when keeping the thermal stress field constant. The theoretical fundamentals of the method are based on Maysel's formula of uncoupled thermoelasticity. The numerical examples show the effectiveness and reliability of the proposed algorithm.     

Axisymmetric and One-Dimensional Thermoelastic Fields of Radially Graded Bodies

In this paper, both Young's modulus and Poisson's ratio along with thermal expansion coefficient are allowed to vary across the radius in a solid ring and a curved beam. Effects of non-constant Poisson's ratio on the thermoelastic field in these graded axisymmetric and one-dimensional problems are studied. A governing differential equation in terms of stress function is obtained for general axisymmetric and one-dimensional problems. Two linearly independent solutions in terms of hypergeometric functions are then attained to calculate the stresses and the strains. Using Green's function method, a form of a solution for the stress functions in terms of integral equations for a curved beam and a solid ring are obtained. Specifically, closed form solutions for the stress functions, when Young's modulus and Poisson's ratio are expressed as power law functions across the radius, are calculated. The results show that the effect of varying Poisson's ratio upon the thermal stresses is considerable for the solid ring. In addition, a non-constant Poisson's ratio has significant influences on the thermal strain field in solid rings. The effect of varying Poisson's ratio upon the thermal stresses is negligible for the curved beam. However, non-constant Poisson's ratios have substantial effects on the thermal strain field in curved beams. Finally, the effects of varying Poisson's ratio on the thermal stresses in thick solid rings and curved beams are also investigated.     

NUMERICAL SOLUTIONS OF THERMOELASTIC WAVE PROBLEMS BY THE METHOD OF CHARACTERISTICS

This article is concerned with the numerical treatment of thermal and thermal stress waves in thermoelastic solids. To keep the numerical treatment general, the development of the formulation is based on the generalized theory of thermoelasticity. A number of thermoelastic wave problems, which involve one or two space variables, are treated, in a uniform manner, by a system of first-order partial differential equations with stress, velocity, heat flow, and temperature as dependent variables. This system of equations is analyzed by the method of characteristics, yielding the characteristics and the characteristic equations. Procedures of numerical integration along the characteristics are established and carried out for several generalized and classical thermoelastic wave problems in homogeneous materials, composite materials, nonhomogeneous materials, and nonlinear elastic solids.