STUDY ON LOCAL DELAMINATED THERMAL BUCKLING OF COMPOSITE LAMINATED PLATES

Based on the Whitcomb delaminated buckling model, a Rayleigh-Ritz analysis is presented to study the local thermal buckling problem of elliptical, rectangular, triangular, and lemniscate delaminations in a symmetric composite laminated plate. The critical temperatures of the laminated plate with various shaped local delaminations and different stacking patterns are obtained by utilizing the energy principle. The geometrical axis of various shapes of local delamination is arbitrary. The stacking sequence of base laminated plates is symmetric, but the stacking sequence of the sublayer is asymmetric. Finally, our experimental study on the mechanism of delaminated buckling failure in a laminated plate with a single elliptical and rectangular delamination near the surface of the laminated plate under thermal load was accomplished. Analytical predictions for the critical temperature yielding the local delamination buckling are shown to correlate well with experimental results for a number of different delamination shapes.     

SHEAR DEFORMATION EFFECTS ON THERMALLY INDUCED INSTABILITY OF LAMINATED PLATES

A theoretical investigation of dynamics for linear elastic moderately thick structures due to uniform space- and time-dependent temperature fields is presented. The structures aredescribed by partial differential equations including a transverse inertia term for a general deformation state with interlaminar shear strains. A viscous model of external damping with a constant proportionality coefficient is assumed to describe a dissipation of the structural energy in the transverse motion. The particular problem of dynamic cylindrical bending due to the temperature with Gaussian and harmonic distributions is analyzed in detail. Dynamic thermal buckling of both symmetric alternating cross-ply composite plates and antisymmetric angle-ply composite laminates is investigated. The influence of neglecting the shear effects on dynamic stability regions is shown.     

EFFECTS OF TEMPERATURE-DEPENDENT PHYSICAL PROPERTIES ON THE RESPONSE OF THERMALLY POSTBUCKLED PLATES

It is known that the values of physical properties, such as the moduli of elasticity and thermal expansion coefficients, cannot be assumed constant over a wide range of high-temperature applications. We therefore examine how the linear temperature variations of physical properties would affect the static and dynamic responses of thermally postbuckled plates. It is found for a clamped aluminum plate that the postbuckled maximum displacement, static x-strain, and root-mean-squared (RMS) x-strain are increased by the same order-of-magnitude percent jump in the thermal expansion coefficient. On the other hand, the critical buckling temperature, x-stress, and RMS x-stress are all decreased by the same order-of-magnitude percent drop in Young's modulus. These observations have also been collaborated with the available composite plate computations. Therefore, this provides an overall estimate on temperature dependency based on the linear temperature variations of physical properties over the operating temperature range.     

太阳电池用Mo纳米薄膜结构演化及热膨胀分子动力学模拟

基于改进嵌入原子法(MAEAM)对Mo纳米薄膜进行了分子动力学(MD)模拟。研究表明,随着温度的上升,薄膜中原子振动变得剧烈,体系混乱程度增加;纳米薄膜的熔点与块体相比明显降低,当薄膜厚度为2.448nm时,其熔点从2895K下降到1800K。纳米薄膜热膨胀系数随温度的升高呈非线性增加,但是在相同温度下,纳米薄膜的膨胀系数比块体的大,并且尺寸越小,热膨胀系数越大,对于厚1.56nm的薄膜其热膨胀系数几乎是块体的两倍,呈现出明显的尺寸效应。比较Mo纳米薄膜与CuInGaSe(CIGS)晶体的膨胀系数,发现在很大温度范围内其差值仅约为15%,说明在薄膜太阳电池中采用Mo薄膜作为背接触衬底将有利于形成高质量的CIGS晶体,达到较高的光电转换效率。     

Computational fluid dynamics analysis of solid oxide electrolysis cells with delaminations

Due to thermal expansion mismatch, the electrode layer of SOECs might be detached from the electrolyte layer, leading to delamination phenomenon. While this phenomenon is observed in post-test stacks, quantitative understanding of delamination effects may facilitate to evaluate SOEC performance tolerance on such failures. In this research, a 2-D CFD SOEC model is developed and is utilized to investigate the sensitivity of electrolysis performance to deliminations occurred at oxygen electrode/electrolyte interface. Results indicate that delaminations significantly influence local charge current density distributions since the charge transport path is cutoff. In both parallel flow and counter flow settings, electrolysis performance is more sensitive to the delamination occurred at the center of the cell than those occurred at the edges of the cell.     

A NEW MODEL OF FUNCTIONALLY GRADED COATINGS WITH A CRACK UNDER THERMAL LOADING

A new model for fracture analysis oaf functionally graded materials (FGMs) with arbitrarily varying material properties under thermal loading is developed. The FGM is modeled as a multilayered medium and in each layer both shear modulus and thermal conductivity are assumed to be a linear function of the depth and are continuous on the subinterfaces. To make the crack problem tractable, thermal expansion and conductivity of the FGMs are supposed to have the same form. With this new model, the crack problem of a functionally graded coating bonded to a homogeneous substrate under steady-state thermal loading is investigated. Employment of the Fourier integral transform technique reduces the problem to a system of Cauchy singular integral equations that are solved numerically. Thermal stress intensity factors (TSIFs) are obtained for various forms of thermal conductivity or expansion. The results reveal that the present model is very efficient and in the frame of the present model both the form of thermal conductivity/expansion and that of its derivative can influence the TSIFs significantly.     

Thermal Fracture Analysis Of Nonhomogeneous Plate with Interfaces Under Uniform Heat Flow

The mixed-mode thermomechanical fracture problem in a nonhomogeneous material plate with two interfaces is studied in this research. Uniform heat flow conditions are considered. The interaction energy integral method for the thermal fracture problem is developed to calculate the thermal stress intensity factors (TSIFs) in nonhomogeneous materials. This method is proved to be domain independent for nonhomogeneous materials even when the integral domain is cut by one interface or many interfaces. Combining the interaction energy integral method with the extended Finite Element Method (XFEM), the temperature fields, the displacement fields, the thermal stress fields, and the TSIFs are calculated. In this article, both the edge crack and the internal crack are considered. Some examples are presented to study the influence of the material properties on the TSIFs. It can be found that the mismatch of the elastic modulus and thermal expansion coefficient can affect the TSIFs dramatically; however, the thermal conductivity interface will not arouse a kinking behavior of the TSIFs. It can be concluded that the existence of an interface (especially for elastic modulus and thermal expansion coefficient) affects the TSIFs greatly.     

EVALUATION OF THERMAL STRESSES INDUCED IN ANISOTROPIC MATERIAL DURING THERMAL SHOCK

In machines and structures operating in a high-temperature environment, such as a turbine blade or a cutting tool, repeated thermal shock is known to induce damage and fracture. Such damages are big problems in technical fields. In developing a good material with a high resistance to thermal shock, it is essential to conduct a quantitative evaluation of the thermal stresses induced in the material during the thermal shock. However, until recently, there have been few methods to evaluate the thermal stresses quantitatively at a given instant of the thermal shock. As an experimental method for the quench-type thermal shock, the present authors proposed the new method that enables us to evaluate the thermal stresses quantitatively. Using this method, we succeeded in clarifying the characteristics of thermal shock of several materials, such as ceramics, cemented carbide, and cermets. However, the influence of the material anisotropy on the thermal stresses induced by the thermal shock is still unknown. In the present study, we perform the thermal shock experiment using two kinds of materials with different degrees of the material anisotropy. From the experiment, it is clarified that the thermal stresses induced by the thermal shock vary with the material anisotropy. A similar result was also obtained using the finite element method (FEM) simulation, which covers a wide range of the material anisotropy. A simple expression was found via simulations used to evaluate the thermal stresses when the material has anisotropies in physical properties, such as Young's modulus and a linear expansion coefficient.     

NONISOTHERMAL CHARACTERIZATION OF THIN-FILM OSCILLATING BEARINGS IN THE PRESENCE OF ULTRAFINE PARTICLES

The effects of viscous dissipation and thermal dispersion due to the presence of ultrafine particles in the lubricating fluid are studied on flow and heat transfer inside a non-isothermal and incompressible bearing during relief and squeezing stages. The governing equations are nondimensionlized and reduced to simpler forms based on an order-of-magnitude analysis. Analytical solution for the energy equation for a special case is obtained. Further, the influence of the thermal squeezing parameter, Eckert number, thermal dispersion coefficient, the motion characteristics of an oscillating bearing, and the perturbation parameter are determined. It is shown that the average heat transfer parameter decreases by an increase in the thermal squeezing parameter and dispersion coefficient, while it increases as both the Eckert number and amplitude motion parameter are increased.     

Effects of nonlinear hygrothermomechanical loading on bending of FGM rectangular plates resting on two-parameter elastic foundation using four-unknown plate theory

In the present study, a simple four-unknown exponential shear deformation theory is developed for the bending of functionally graded material (FGM) rectangular plates resting on two-parameter elastic foundation and subjected to nonlinear hygrothermomechanical loading. The elastic properties, coefficient of thermal expansion, and coefficient of moisture expansion of the plate are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of volume fractions of material constituents. Unlike first-order and other higher-order plate theories, the present theory has four independent unknowns. The in-plane displacement field of the present theory uses exponential functions in terms of thickness co-ordinate for calculating out-of-plane shearing strains. The transverse displacement includes bending and shear components. The principle of virtual displacement is employed to derive the governing equations and associated boundary conditions. A Navier solution technique is employed to obtained an analytical solutions. The elastic foundation is modelled as two-parameter Winkler–Pasternak foundation. The numerical results obtained are compared with previously published results wherever possible to prove the efficacy and accuracy of the present theory. The effects of stiffness and gradient index of the foundation on the hygrothermomechanical responses of the plates are discussed.     

THERMOMECHANICAL BEHAVIOR OF THE SOLIDIFYING SHELL WITHIN CONTINUOUS-CASTING BILLET MOLDS-A NUMERICAL APPROACH

A two-dimensional numerical model is given for the analysis of the coupled thermal and mechanical behavior of the solidifying shell within the mold during continuous casting of steel. The influence of different mold wall profiles on gap formation and heat flow during casting of billets is investigated. The calculated temperatures, stresses, and strains in the shell are used to estimate the risk for formation of longitudinal cracks. The effect of an initiated and growing macroscopic subsurface crack on the shell behavior is studied. The genesis of surface cracks is discussed. The calculated results are shown to be in reasonable agreement with experimental observations reported in the literature.     

太阳电池板结构应力-应变状态分析

多层胶接是太阳电池板的结构特点,由于不同材料的弹性模量、热膨胀系数和泊松比不同,在温度场 作用下会产生热应力应变,在多次热交变过程中热应力．应变累积最后导致结构层间剥离,因此研究温度场作用 下太阳电池板结构应力应变状态具有非常重要的实际意义。本文推导了模拟太阳电池板结构应力-应变状态的一 维模型,该模型同样适用于分析多层胶接结构应力应变状态。     

BUCKLING BEHAVIOR OF LONG ANISOTROPIC PLATES SUBJECTED TO RESTRAINED THERMAL EXPANSION AND MECHANICAL LOADS

An approach for synthesizing buckling results and behavior for thin balanced and unbalanced symmetric laminates that are subjected to nondestabilizing mechanical preloads, uniform heating or cooling, and elastically or totally restrained axial thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined loads and is based on useful nondimensional parameters. In addition, a stiffness-weighted laminate coefficient of thermal expansion is derived and used to determine critical temperatures in terms of physically intuitive mechanical buckling coefficients, and the effects of membrane orthotropy and membrane anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the article. Several generic buckling design curves are presented that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves. The analysis approach and generic results identify the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.     

简单机械零件热变形行为研究及应用

精密机械零件的受温变形一般是用热膨胀的概念来解释和补偿的，而热膨胀系数的不确定性直接影响着补偿的精度。为此，本文利用一套高精度测量系统，对形体的主要几何参数进行受温变形研究，并从振动的角度对形体的热变形进行理论分析，理论和试验的方差分析都表明：球体直径的热变形系数与边界条件无关，而其它形体的热变形系数却与边界条件有关。     

NUMERICAL ANALYSIS OF THERMAL STRESSES IN A NONLINEAR THERMOELASTIC THICK CYLINDRICAL SHELL AND CUBE

Numerical analysis of static thermal stresses in a nonlinear, isotropic, thermaelas-tic, thick cylindrical shell and a cube is presented using the nonlinear thermoelas-ticity. The geometrical relations, equilibrium equations, and Fourier's law are linear while the constitutive relations accounting for the id-order elastic moduli and the temperature-dependent 2d-order elastic moduli and coefficient of thermal expansion are nonlinear. Nonlinear effects are numerically investigated for a cylindrical shell and a cube made of D54S aluminum alloy.

     

Thermal Stress Analysis of Sandwich Structures

ABSTRACT

Significant thermal and interlaminar transverse stresses often occur in sandwich structures subjected to thermal loading due to the mismatch in thermal expansion of different materials in structures. A kind of 32-node, 3-layered shell element with relative degrees-of-freedom accompanied by a post-processing method is presented based on 3D FEM to accurately describe thermo-structures behavior and easily connected with brick elements. The present method is verified by a theoretical result. The thermal stress fields in a sandwich cylinder with a cutout with and without reinforcement are calculated by the method successfully. The results show that reinforcement may cause significant transverse thermal stresses, although it is beneficial to reducing in-plane stress.     

THERMAL STRESSES IN A NONHOMOGENEOUS THICK PLATE UNDER STEADY DISTRIBUTION OF TEMPERATURE

This paper is concerned with a method for calculating the thermal-stress distribution in a nonhomogeneous medium whose shear modulus and coefficient of thermal expansion are assumed to be functions of z. The solution of the problem is determined by using displacement functions. A solution is then derived for the thermal-stress distribution in a nonhomogeneous, thick elastic plate under steady distribution of the surface temperature. Numerical results are presented.     

Application of Simplex Search Method for Predicting Unknown Parameters in an Annular Fin Subjected to Thermal Stresses

This article presents an inverse approach aimed at estimating the unknown parameters such as the coefficient of thermal expansion and the Biot number for satisfying a prescribed thermal stresses field in radial fin geometry. The variation of temperature with the radius of fin is obtained by solving the heat conduction-convection equation using regular perturbation method and applying proper boundary conditions. A closed form solution for the temperature dependent stress field has been derived by employing the classical elasticity theory coupled with semi-analytical solution for the temperature field. Using the data obtained from a forward method based on the analytical solution, two unknown parameters such as the coefficient of thermal expansion and the Biot number of the fin are simultaneously estimated by an inverse technique using the Nelder-Mead simplex search method. Effects of measurement errors and number of measurement points have been analyzed in detail. It is found that even with 10 measurement points a fairly good reconstruction of the stress field can be achieved.     

EFFECT OF THERMAL RESIDUAL STRESS ON THE INTERLAMINAR CRACK EXTENSION BEHAVIOR IN CROSS-PLY LAMINATES DUE TO TRANSVERSE LOADING

The effect of thermal residual stress on the two-dimensional interlaminar crack extension behavior in a cross-ply laminate subjected to transverse loading is estimated. Attention is focused on the contribution of thermal residual stress to the local energy release rate along the interlaminar crack front. Computational simulations are carried out on the basis of constant critical energy release rates in order to examine implicitly how the two-dimensional size and shape would be changed by the presence of thermal residual stress. A considerably large amount of energy is found to be supplied for the interlaminar crack extension by thermal residual stress, while little influence is perceived with respect to the apparent extension behavior including the shape of the interlaminar crack.     

Heat and Mass Transfer by Mixed Convection from a Vertical Slender Cylinder with Chemical Reaction and Soret and Dufour Effects

This work is focused on the study of heat and mass transfer by mixed convection over a vertical slender cylinder in the presence of chemical reaction and thermal‐diffusion and diffusion‐thermo effects. The resulting equations have the property whereby they reduce to various special cases previously considered in the literature. An adequate implicit, tri‐diagonal finite‐difference scheme is employed for the numerical solution of the obtained equations. Various comparisons with previously published work are performed and the results are found to be in excellent agreement. Representative results for the local skin‐friction coefficient, local Nusselt number, and the local Sherwood number illustrating the influence of the surface transverse curvature parameter, Richardson number, concentration to thermal buoyancy ratio, Schmidt number, chemical reaction, and the Dufour and Soret numbers are presented and discussed. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(7): 618–629, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21045