超超临界汽缸高温强度及多轴蠕变分析

超超临界汽轮机汽缸的多轴蠕变分析与高温强度设计对机组安全高效运行至关重要.对于在超超临界参数下中压内缸,它的主要破坏来自于高温和复杂应力共同作用下的蠕变损伤.随着蒸汽参数(温度T,压力P)的不断提升,原汽缸承受的蠕变损伤越发严重,因此有必要进行局部结构改进.应用基于受约束孔洞长大机制的Cocks-Ashby多轴蠕变模型对新老汽缸进行了对比分析,并采用了有限元计算方法得到了汽缸多轴蠕变等效应变的分布.结果表明:基于孔洞长大蠕变理论能较好地预测汽缸危险点的多轴蠕变;新汽缸比老汽缸在抗蠕变性能方面有一定改善.     

汽缸结构上下缸接触的有限元分析

采用有限元软件MSC／NASTRAN计算分析了汽轮机汽缸结构上下缸接触状态的应力分布和变形．分析了汽缸在温度场作用下以及温度场同内压联合作用下的应力分布情况，重点分析上下半缸的螺栓连接面——中分面上的应力和变形情况．建立了气缸三维实体有限元分析模型，并对每根连接螺栓均建立了模拟模型．分析结果表明，同内压引起的应力相比，热应力是缸体中应力的主要成分．当内外壁温差达到100℃时，缸体中最大应力为1230MPa，出现在约束处应力集中部位，缸体绝大部分应力水平在600-700MPa；汽缸外壁温度为250℃时，缸体中最大应力为1080MPa，缸体绝大部分应力水平在100MPa，得出减小汽缸内外壁的温差能有效减小缸体中应力的结论．分析表明，缸体轴向最大伸长量为2．55mm，横向最大变形为2．02mm．Z向最大位移为1．24mm．中分面有分离，但分离程度较小，分离值均在10^—3mm量级上．     

三种壳体在脉冲电子束辐射下动力学响应的实验研究

在闪光二号电子束装置上 ,对材料或形状有异的两端固支的三种壳体进行了辐射结构响应的实验研究。实验采用在壳体内表面粘贴一个特制长引线应变片并组成直流桥路的测量原理。结果表明 :当壳体受辐射方位角为 0～ 180时 ,应变峰值随方位角的增大而减小 ;编织材料壳体中的应变峰值和热激波应力峰值都比硬铝壳体中的小 ;当电子束能注量为 15 0～ 2 10J/cm2 、壳体半径厚度比为 13～ 18 5时 ,壳体变形处于弹塑性或全塑性状态。     

谷粒的热——湿应力分析

针对谷物烘干问题,本文研究弹性及粘弹性圆球和椭球的热,湿应力。对圆球分析表明,热应力峰值远比湿应力峰值出现时间早,在假定材料为热,湿流变简单的Maxwell粘弹性体条件下,本文导出了圆球的热,湿应力分布公式,并应用有限元法研究了椭球的热,湿应力,文中以无量纲形成给出了圆球中心和表面应力随时间的 变化情况,以及椭球中心轴向应力峰值随椭球长,短半轴之比的变化情况。     

卫星用复合材料压力容器力学特性研究

为了研究航天复合材料压力容器内衬与复合材料双层壳体的力学特性,通过优化复合材料网格理论算法,针对钛合金内衬(TC4)/碳纤维(T1000GB)缠绕柱形复合材料压力容器进行了应力应变特性分析.以纤维预紧应力为自变量,研究其对内衬/纤维双层壳体在预紧压力、工作压力、验证压力和爆破压力下应力的影响,提出了优化设计的解析解法,指出内衬与复合层力学特性对容器性能的影响机理,为结构设计和同类产品设计提供了计算方法和理论指导.     

封装光纤线圈的胶粘剂对光纤产生的热应力影响

分析了外加应力对光纤消光比的影响，对封装后的光纤线圈建立了简化的力学模型。根据弹性力学原理，利用有限元分析方法对其进行热应力分析，结果表明通过减小胶粘剂的热变形量可以减小对光纤的热应力影响。此外还进行了实验验证，所得实验结果与理论分析基本符合。     

用Hamilton半解析法分析固化降温过程中的层间热应力

推导了增量形式Ｈａｍｉｌｔｏｎ半解析法公式；给出了层合板瞬态热弹性问题的求解过程；对复合材料层合板在固化降温过程中的热应力进行了分析。结果表明，在降温过程中层合板内将会出现较大的应力峰值，这些应力峰值将是导致层合板在固化工艺过程中出现破坏的原因。本文的工作将对固化工艺研究具有参考价值。     

材料的本构关系与非线性有限元

一、引言随着工程科学的进展,对非线性固体介质进行力学分析的需要变得日益迫切。高速飞行器的热应力、再入卫星的头部烧蚀和变形、喷气发动机各部件的应力集中、反坦克弹的变形及反应堆壳体的蠕变等等问题的研究,都与材料的非线性特性有关,对金属固体来说,特别与弹塑性特性有关。现代断裂理论的研究也必须研究裂纹顶端的应力应变场,这里弹塑性是重要的因素。在数学上,这种非线性分析常常是一个依赖于应力历史的、与路径有关的复杂问题,这就引起了数学家的注意。但是应该说,在高速大型计算机未出现之前,光靠解析数学工具,我们是无能为力的。      

考虑非傅里叶微尺度效应涂层基体复合结构热冲击强度研究

针对在涂层热冲击研究中忽略非傅里叶传热微尺度效应的问题,本文引入一维平板涂层基体复合结构物理模型,建立涂层双曲线型传热、基体抛物线型传热的数学模型Ⅰ,并根据交界面处的传热行为建立合理边界条件.在此基础上,构建了涂层、基体的热弹性力学模型.采用隐式差分法对模型离散化处理,得到温度场的数值解,进而求得应力场,并给出了具体算例.同时,建立涂层和基体均为抛物线型传热的数学模型Ⅱ作为对比研究.结果表明：当初始条件和热扰动均相同,并考虑非傅里叶传热的微尺度效应时,在涂层内,模型Ⅰ热应力表现出变化的延迟性、分布的局域性以及波动性,任意位置热应力都不是从0开始变化,而模型Ⅱ不存在波动性,任意位置热应力从0开始变化.模型Ⅰ热应力产生后,率先达峰且峰值大于模型Ⅱ.在基体内,模型Ⅰ热应力大于模型Ⅱ,且变化梯度较大.在交界面处,模型Ⅰ产生“反射效应”,此处应力值以及应力骤降值均大于模型Ⅱ.对比表明,模型Ⅰ受到的热冲击更加复杂剧烈.该研究为极端热传导环境下确保涂层可靠性提供了有益参考.     

热应力作用下结构声-振耦合响应数值分析

考察飞行器结构热应力对结构及其内声腔声-振耦合特性的影响,建立考虑热应力因素的声-振耦合动力学有限元方程,对一个典型飞行器结构考虑热应力时的声-振耦合动力学响应进行分析。计算结果表明,热应力的存在对耦合模型的固有频率影响较小,受热应力影响较大的区域主要集中在机头及机身等部位,其固有振动特性有较明显的变化。通过对比结构加速度与内声腔声压级的响应结果发现,热应力的影响主要表现为系统响应幅值及峰值位置的改变。     

热对流作用下筒壁涂层的边裂行为

边裂(边缘开裂)是涂层热致损伤的主要模式之一. 边缘裂纹穿透涂层后,常导致界面脱粘从而驱使涂层与基体剥离,最终丧失对基体的保护作用. 本文以热应力强度因子表征边缘裂纹的扩展驱动力,研究筒壁涂层在热对流作用下的边裂行为. 首先,利用拉普拉斯变换法,得到了瞬态温度场及热应力场的封闭解. 其次,运用Fett等的三参数法确定了筒壁涂层边缘裂纹的权函数. 最后,基于叠加原理和权函数方法计算了边缘裂纹的热应力强度因子. 探讨了无量纲时间、边缘裂纹深度、基体/涂层厚度比、热对流强度等参数对热应力强度因子的影响规律. 结果表明:热应力强度因子的峰值既非发生在热载荷初始时刻,也非发生在热稳态时刻,而出现在时间历程的中间时刻;增大热对流强度不仅可提高热应力强度因子的峰值,而且使峰值提前出现;其他条件相同时,热应力强度因子随着边缘裂纹长度的增大而降低;增大涂层厚度或减小基体厚度可增强涂层抵抗瞬态热载荷的能力.      

Practical Green's function for the thermal stress field induced by a heat source in plane thermoelasticity

The classical Green’s functions used in the literature for a heat source in a homogeneous elastic medium cannot lead to finite remote thermal stresses in the medium, so that they may not work well in practical thermal stress analyses. In this paper, we develop a practical Green’s function for a heat source disposed eccentrically into an elastic disk/cylinder subject to plane deformation. The edge of the disk/cylinder is assumed to be thermally permeable and traction-free. The full thermal stress field induced by the heat source in the disk/cylinder is determined exactly and explicitly via the Cauchy integral techniques. In particular, a very simple formula is obtained to describe the hoop thermal stress on the edge of the disk/cylinder, which may be conveniently useful for analyzing the thermal stresses in microelectronic components.     

圆柱外表面受热冲击问题的广义热弹性分析

基于 L-S 广义热弹性理论, 针对实心圆柱体在外表面受均匀热冲击作用下的一维广义热弹性问题进行研究分析. 利用热冲击的瞬时特征, 借助于 Laplace 正、反变换技术及柱函数的渐近性质, 推导了热冲击作用周期内温度场、位移场和应力场的渐近表达式. 通过计算, 得到了热冲击条件下各物理场的分布规律以及延迟效应和耦合效应对热弹性响应的影响规律. 结果表明: 当考虑延迟效应和耦合效应时, 热扰动将以两组速度不同的波的形式向前传播, 延迟效应和耦合效应对各物理场的建立时间, 阶跃间隔和阶跃峰值均产生影响, 且延迟效应和耦合效应均在一定程度上削弱了热冲击的作用效果.      

Transient thermal cracking associated with non-classical heat conduction in cylindrical coordinate system

This paper studies the fracture behavior of a thermoelastic cylinder subjected to a sudden temperature change on its outer surface within the framework of non-classical heat conduction.The heat conduction equation is solved by separation of variable technique.Closed form solution for the temperature field and the associated thermal stress are established.The critical parameter governing the level of the transient thermal stress is identified.Exact expression for the transient stress intensity factor is obtained for a crack in the cylinder.The difference between the non-classical solutions and the classical solution are discussed.It is found that the traditional classical heat conduction considerably underestimates the transient thermal stress and thermal stress intensity factor.     

Crack spacing effect for a piezoelectric cylinder under electro-mechanical loading or transient heating

This paper investigates the fracture problem of a piezoelectric cylinder with a periodic array of embedded circular cracks. An electro-mechanical fracture mechanics model is established first. The model is further used to the thermal fracture analysis of a piezoelectric cylinder subjected to a sudden heating on its outer surface. The temperature field and the associated thermal stresses and electric displacements are obtained and are added to the crack surface to form a mixed-mode boundary value problem for the electro-mechanical coupling fracture. The stress and stress intensities are investigated for the effect of crack spacing. Strength evaluation of piezoelectric materials under the transient thermal environment is made and thermal shock resistance of the medium is given.     

Transient thermal elastic fracture of a piezoelectric cylinder specimen

A finite piezoelectric cylinder with an embedded penny-shaped crack is investigated for a thermal shock load on the outer surface of the cylinder. The theory of linear electro-elasticity is applied to solve the transient temperature field and the associated thermal stresses and electrical displacements without crack. These thermal stresses and electrical displacements are added to the surfaces of the crack to form an electromechanical coupling and mixed mode boundary-value problem. The electrically permeable crack face boundary condition assumption is used, and the thermal stress intensity factor and electrical displacement intensity factor at the crack border are evaluated. The thermal shock resistance of the piezoelectric cylinder is evaluated for the analysis of piezoelectric material failure in practical engineering applications.     

Dynamic thermal shock in a layered cylinder with initial interface pressure

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Thermal stresses in infinite circular cylinder subjected to rotation

The present investigation is concerned with the effect of rotation on an infinite circular cylinder subjected to certain boundary conditions.An analytical procedure for evaluation of thermal stresses,displacements,and temperature in rotating cylinder subjected to thermal load along the radius is presented.The dynamic thermal stresses in an infinite elastic cylinder of radius a due to a constant temperature applied to a variable portion of the curved surface while the rest of surface is maintained at zero temperature are discussed.Such situation can arise due to melting of insulating material deposited on the surface cylinder.A solution and numerical results are obtained for the stress components,displacement components,and temperature.The results obtained from the present semi-analytical method are in good agreement with those obtained by using the previously developed methods.     

Transient thermal stresses in two-dimensional functionally graded thick hollow cylinder with finite length

In this paper transient thermal stresses in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) based on classical theory of thermoelasticity are considered. The volume fraction distribution of materials, geometry and thermal load are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with graded material properties within each element is used to model the structure. Temperature, displacements and stress distributions through the cylinder at different times are investigated. Also the effects of variation of material distribution in two radial and axial directions on the thermal stress distribution and time responses are studied. The achieved results show that using 2D-FGM leads to a more flexible design so that time responses of structure, maximum amplitude of stresses and uniformity of stress distributions can be modified to a required manner by selecting suitable material distribution profiles in two directions.     

Multiple axial cracks in a coated hollow cylinder due to thermal shock

The transient thermal stress problem of an inner-surface-coated hollow cylinder with multiple pre-existing surface cracks contained in the coating is considered. The transient temperature, induced thermal stress, and the crack tip stress intensity factor (SIF) are calculated for the cylinder via finite element method (FEM), which is exposed to convective cooling from the inner surface. As an example, the material pair of a chromium coating and an underlying steel substrate 30CrNi2MoVA is particularly evaluated. Numerical results are obtained for the stress intensity factors as a function of normalized quantities such as time, crack length, convection severity, material constants and crack spacing.