Thermal Buckling Analysis of Perforated Functionally Graded Plates

In this research, the buckling behavior of functionally graded (FG) plates under thermal loading is investigated based on finite element analysis. It is assumed the plate is subjected to a uniform temperature rise across plate thickness. First-order shear deformation theory (FSDT) is utilized for developing the solution method. By using an appropriately designed mesh structure for a perforated plate, the critical thermal buckling temperature is obtained by numerical solution of the problem based on finite element method (FEM). The FG plate is perforated by multiple cutouts. The number of cutouts is assumed one, two, four, or six. Also different geometrical shapes of cutouts including triangle, square, rhombus, pentagon, hexagon, and circle are considered. The influence of the number of cutouts and their geometrical shapes on thermal buckling response is investigated. The effects of the number of sides of cutouts from three (triangle) to infinity (circle) are discussed. Two different boundary conditions are taken into account. Also the influences of the distance between the cutouts and the orientation of cutouts on critical buckling temperature are studied. In addition, the effects of the orientation of ellipse cutouts are studied. Some remarkable conclusions are gained that can be useful in practical applications.     

Mechanical Behavior of Rectangular Plates with Functionally Graded Coefficient of Thermal Expansion Subjected to Thermal Loading

This study analyzed an elastic, rectangular, and simply supported functionally graded material (FGM) plate with medium thickness subjected to linear temperature change in the z direction. Young's modulus and Poisson ratio of the FGM plates are assumed to remain constant throughout the entire plate. However, the coefficient of thermal expansion of the FGM plate varies continuously throughout the thickness direction in relation to the volume fraction of constituents defined by power-law, sigmoid, or exponential functions. The series solutions for the power-law FGM (P-FGM), sigmoid FGM (S-FGM), or exponential FGM (E-FGM) plates subjected to thermal loading are obtained based on the classical plate theory and Fourier series expansion. The analytical solutions for P-, S-, and E-FGM plates are verified by numerical results obtained with the finite element technique.     

A Refined Sine Finite Element with Transverse Normal Stress for Thermoelastic Analysis of Laminated Composite in Cylindrical Bending

An unidimensional three-node composite finite element including the transverse normal effect is presented in the framework of the thermoelastic coupling. The kinematics is based on a sinus distribution with layer refinement and a second-order expansion for the deflection. The calculation of the transverse normal stress comes from a weak formulation and takes into account the physical considerations. Numerical results for displacements and stresses are provided for very thick and thin structures in cylindrical bending. They are compared with exact elasticity solution and the results are promising.     

Exact Solution for Thermal Buckling of Functionally Graded Plates Resting on Elastic Foundations with Various Boundary Conditions

In this article, we investigate the buckling analysis of plates that are made of functionally graded materials (FGMs) resting on two-parameter Pasternak's foundations under thermal loads. Three different thermal loads were considered, i.e., uniform temperature rise (UTR), linear and non-linear temperature distributions (LTD and NTD) through the thickness. The mechanical and thermal properties of functionally graded material (FGM) vary continuously along the plate thickness according to a simple power law distribution. Employing an analytical approach, the five coupled governing stability equations, which are derived based on first-order shear deformation plate theory, are converted into two uncoupled partial differential equations (PDEs). Considering the Levy-type solution, these two PDEs are reduced to two ordinary differential equations (ODEs) with variable coefficients. Then, the ODEs are solved using an exact analytical solution, which is called the power series Frobenius method. The appropriate convergence study and comparison with previously published related articles was employed to verify the accuracy of the proposed method. After such verifications, the effects of parameters such as the plate aspect ratio, side-to-thickness ratio, gradient index, and elastic foundation stiffnesses on the critical buckling temperature difference are illustrated and explained. The critical buckling temperatures of functionally graded rectangular plates with six various boundary conditions are reported for the first time and can serve as benchmark results for researchers to validate their numerical and analytical methods in the future.     

Thermal Buckling of Functionally Graded Plates According to a Four-Variable Refined Plate Theory

In this article, a four-variable refined plate theory is presented for buckling analysis of functionally graded plates. The theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The influences of many plate parameters on buckling temperature difference will be investigated. It is noticed that the present refined plate theory can predict accurately the critical temperatures of simply supported functionally graded plates.     

Thermoelastic Buckling Analysis of Functionally Graded Circular Plates Integrated with Piezoelectric Layers

Thermal buckling of circular plates made of functionally graded materials with surface-bounded piezoelectric layers are studied. The material properties of the FG plates are assumed to vary continuously through the plate thickness by distribution of power law of the volume fraction of the constituent materials. The general thermoelastic nonlinear equilibrium and linear stability equations for the piezoelectric FG plate are derived using the variational formulations. Buckling temperatures are derived for solid circular plates under uniform temperature rise, nonlinear and linear temperature variation through the thickness for immovable clamped edge of boundary conditions. The effects of piezo-to-host thickness ratio, applied actuator voltage, boundary condition, and power law index of functionally graded plates on the buckling temperature of plate are investigated. The results are verified with the data in literature.     

Selection of Displacement Parameters in Zig-Zag Models for Thermal Analysis of Laminated Composite Plates

The zig-zag theory is well developed in the analysis of laminated structures as the continuity requirement of stresses between plies are a priori satisfied. If the derivatives of lateral displacements are retained in the final displacement field, a C ¹-type zig-zag model is resulted for the finite element analysis. If all the derivatives of lateral displacements are eliminated, we can have a C ⁰-type finite element model, in which only C ⁰ interpolation functions are required. Thus, this article proposed a new C ⁰-type zig-zag theory considering transverse normal strain for thermal stress analysis of laminated plates. In line with the theoretical prediction, analytical series solutions developed in this article indicate that C ⁰ model is more accurate than the C ¹ model in the analysis of composite plates subjected to thermal loads.     

柴油机活塞热冲击问题有限元分析

利用Galerkin法原理,建立了轴对称热冲击问题的有限元方程,以PA6-280柴油机活塞为例,进行了数值分析,对其热冲击期间应力变化规律做了分析和讨论,其结果表明,本文理论为研究活塞的热冲击及热损伤机理提供了数值分析方面的基础。     

柴油机活塞温度场试验研究及有限元热分析

对改进的ZH1105W型柴油机缩口四角ω燃烧系统,利用热电偶法实测了标定工况下活塞顶面、侧面和内腔共16个特征点的温度.用Pro/E建立活塞几何模型,选取热结构耦合单元,并对模型网格进行了优化,结合试验值对活塞进行热分析计算,得到活塞三维温度场、热应力场和变形.计算结果表明,在标定工况下,活塞最高温度出现在燃烧室喉部达到310.7℃,最大von Mises热应力出现在排气一侧的回油孔顶部,为68.4 MPa,最大热变形量出现在活塞顶面边缘排气口侧,达到0.328 mm,这为活塞的结构改进和优化提供了依据.     

Thermal Buckling of Piezolaminated Plates Subjected to Different Loading Conditions

A thermal buckling analysis is presented for simply supported rectangular laminated composite plates that are covered with top and bottom piezoelectric actuators, and subjected to the combined action of thermal load and constant applied actuator voltage. The thermomechanical properties of composite and piezoelectric materials are assumed to be linear functions of the temperature. The formulations of the equations are based on the higher-order laminated plate theory of Reddy and using the Sanders nonlinear kinematic relations. The closed-form solutions for the buckling temperature are obtained through the Galerkin procedure and solving the resultant eigenvalue problem, which are convenient to be used in engineering design applications. Numerical examples are presented to verify the proposed method. The effects of the plate geometry, fiber orientation in composite layers, lay-up configuration, different utilized piezoelectric materials, temperature dependency of material properties, thermal conductivity, and energy generation on the buckling load are investigated.     

超临界汽轮机高压缸有限元热应力分析

应用有限元分析程序对超临界600MW汽轮机高压缸方案进行三维有限元应力分析，提出采用带有一半圆槽的新型高压隔板套设计方案，可有效降低高压隔板套应力，采用椭圆形汽封结构形式，既可避免动静之间产生碰磨，又能使轴封和隔板汽封有较小的间隙，提高机组热效率，为超临界机组的研究与开发提供理论依据。     

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。     

Thermal Buckling Analysis of a Mindlin Rectangular FGM Microplate Based on the Strain Gradient Theory

This article is aimed at developing a nonclassical Mindlin rectangular functionally graded material (FGM) microplate based on the strain gradient theory (SGT) to study the thermal buckling behavior of microplates with different boundary conditions. This theory comprises material length scale parameters to interpret size effects. The developed model encompasses classical and modified couple stress Mindlin microplate models, if all the material length scale parameters or two of them are taken to be zero, respectively. The Mindlin rectangular FGM microplate is considered to be made of a mixture of metal and ceramic of which the volume fraction is described through a power low function. According to Hamilton's principle and the generalized differential quadrature (GDQ) method, the stability equations and associated boundary conditions are obtained and discretized, respectively. Current formulations provide a possibility to have all types of boundary conditions which herein, FGM microplates with three commonly used boundary conditions are considered. Three different types of thermal loads including uniform, linear and nonlinear temperature rises along the thickness of FGM microplates are considered. The dimensionless critical buckling temperature difference (DCBTD) predicted by SGT is compared with that of modified couple stress theory (CST) and classical theory (CT) which it is found that CST and CT underestimate the DCBTD. Also, effects of the boundary conditions, length scale parameter and material gradient index of FGM microplates on the DCBTD are judiciously investigated.     

Modeling of Fiber-Reinforced Composite Material Subjected to Thermal Load

Two-dimensional thermally loaded structural elements are considered. The elements are made of composite materials in the form of a multi-layer laminate of matrix layers filled with the fibers. In each layer the fraction of fibers and their arrangement in a matrix can be different. The modeling process of thermal properties of such materials, defined by the coefficients of thermal conductivity in the direction of orthotropy axes (fibers and direction perpendicular to them) is discussed. Using the heat balance equation and Fourier's basic law for total balance of heat flux for mixture of fibers and matrix, the substitute conductivity coefficients in orthotropy directions are determined for a variety of cross-sections of filling fibers in particular layer. These coefficients define the macroscopically equivalent homogeneous orthotropic materials of each layer. Next, the substitute conductivity coefficients for the stack of layers are determined, where the layers stack is modeled with one homogenous material. The proposed model of fiber-reinforced laminate was used in some numerical examples. To analyze the problem of heat transfer within a structure domain, the finite element method was applied.     

利用ANSYS对矩形疲劳容器进行有限元应力分析

文中介绍了一台矩形疲劳容器的应力分析,利用ANSYS建立了筒体和人孔装置两部分模型,将应力分类并对各类应力按JB4732标准的要求进行评定,结果显示,该矩形容器在规定的设计条件下的应力能够满足标准的要求。     

Effect of Initial Imperfections on Thermal Buckling of Functionally Graded Plates

ABSTRACT

Thermal buckling analysis of rectangular functionally graded plates with initial geometrical imperfections is presented in this article. The equilibrium, stability, and compatibility equations of an imperfect functionally graded plate are derived using the first-order shear deformation plate theory. It is assumed that the nonhomogeneous mechanical properties of the plate, graded through the thickness, are described by a power function of the thickness variable. The plate is assumed to be under three types of thermal loading, namely: uniform temperature rise, nonlinear temperature rise through the thickness, and axial temperature rise. Resulting equations are employed to obtain the closed-form solutions for the critical buckling temperature change of an imperfect functionally graded plate. The influence of transverse shear on thermal buckling load is discussed.     

DN2机车用喷油嘴的有限元数值分析

本文通过对DN_2机车用喷油嘴针阀体的有限元数值分析,得出了针阀体在机械负荷、液力负荷和热负荷作用下的变形和应力分布的定量值.为喷油嘴设计研究、生产使用、提高喷油嘴工作可靠性提供了依据.     

缸套瞬态温度场的有限元分析

本文提供了计算二维温度场的通用方法,即瞬态温度场的非线性有限元解法.首先,以实测的温度确定缸壁与燃气的接触边界条件,计算出稳定温度场.以稳定温度场做初始条件,考虑活塞运动情况,利用所确定的放热系数确定缸套与燃气的接触边界条件计算了铸铁缸套的瞬态温度场,给出了缸套表面层的温度波动情况.     

Thermal Buckling of Axially Functionally Graded Thin Cylindrical Shell

In the present research, thermal buckling of shell made of functionally graded material (FGM) under thermal loads is investigated. The material properties of functionally graded materials (FGMs) are assumed to be graded in the axial direction according to a simple power law distribution in terms of the volume fractions of the constituents. In the previous articles that published, these properties are assumed to be graded in the thickness direction. Nonlinear kinematic (strain-displacement) relations are considered based on the first order shear deformation shell theory. By substituting kinematic and stress-strain relations of functionally graded shell in the total potential energy equation and employing Euler equations, the equilibrium equations are obtained. Applying Euler equations to the second variation of total potential energy equation leads to the stability equations. Then, buckling analysis of functionally graded shell under three types of thermal loads is carried out resulting into closed-form solutions.     

增压器背盘变形有限元分析

背盘是影响增压器质量的重要因素。本文利用有限元方法分析某型增压器背盘产生较大变形的原因及其背盘结构改进的方向。首先分析了背盘在正常条件下的变形;然后分析了在不正常手持时的背盘变形：最后分析了不正常装配是否会产生较大变形。通过上述几种分析结果获得了该背盘大变形的原因及解决办法。