GREEN'S FUNCTIONS FOR A STEADY HEAT SOURCE IN A TWO-PHASE TRANSVERSELY ISOTROPIC ELASTIC SOLID

Based on the three-dimensional anisotropic thermoelasticity theory, Green's function solutions are presented for a steady heat source in a two-phase transversely isotropic solid. The mirror reflection method is used and a general expression of the solutions in the Cartesian coordinate system is obtained. It is also shown that the solution includes the special cases of a homogeneous transversely isotropic elastic solid of infinite space and of semi-infinite space. In addition, numerical examples for the titanium-zinc composites are given.     

Nonhomogeneous Heat Conduction Problem and Its Thermal Deflection Due to Internal Heat Generation in a Thin Hollow Circular Disk

This article is concerned with the determination of temperature and thermal deflection in a thin hollow circular disk under an unsteady-state temperature field due to internal heat generation within it. Initially, the disk is kept at an arbitrary temperature F(r, z). For times t > 0 heat is generated within the thin hollow circular disk at a rate of g(r, z, t) Btu/hr ft³, while the boundary surfaces at (r = a), (r = b), (z = 0) and (z = h) are kept at temperatures f ₁(z, t) and f ₂(z, t), f ₃(r, t) and f ₄(r, t), respectively. The governing heat conduction equation has been solved by using a finite Hankel transform and the generalized finite Fourier transform. The results are obtained in series form in terms of Bessel's functions. As a special case, different metallic disks have been considered. The results for temperature change and the thermal deflection have been computed numerically and illustrated graphically.     

TRANSIENT THERMAL STRESS PROBLEM IN A TRANSVERSELY ISOTROPIC FINITE CIRCULAR CYLINDER UNDER THREE-DIMENSIONAL TEMPERATURE FIELD

This paper is concerned with a transient thermal stress problem in a finite circular transversely isotropic solid cylinder subjected to an asymmetrical temperature distribution on a cylindrical surface. The stress fields are found by use of potential functions method. As an example, the temperature and stress fields for a specific case are computed for the sake of comparison to the isotropic body.     

Optimal Heating Control of Thermosensitive Rectangular Domain under Restrictions on Stresses in a Plastic Zone

A numerical algorithm to solve the problem on optimal heating control for a long isotropic homogeneous rectangular parallelepiped under plane strain has been proposed. The control (the surrounding temperature at one of the boundary surfaces of a parallelepiped) which in a minimal time, carries the body from the initial thermal state to the final one characterized by the given mean-integral temperature has been determined. In addition, restrictions both to the control function and to the maximal tangential stress intensity have been considered. The case of elastoplastic deformation of the material has been studied in the framework of the theory of the body element deformation along small curvature paths.     

DYNAMIC THERMAL STRESS IN A TRANSVERSELY ISOTROPIC HOLLOW SPHERE

A closed-form solution for the histories and distribution of dynamic themoelastic stress in a transversely isotropic hollow sphere is obtained. The field equation for a spherically symmetric transversely isotropic problem subjected to rapid arbitrary heating shock is derived and solved. Based on the results in this article, some phenomena in a transversely isotropic hollow sphere under thermal shock are shown.     

TRANSIENT THERMOELASTIC SOLUTION OF A MULTILAYERED ORTHOTROPIC HOLLOW CYLINDER FOR AXISYMMETRIC PROBLEMS

The thermoelastic dynamic solution of a multilayered orthotropic hollow cylinder in the state of axisymmetric plane strain is obtained. By the method of superposition, the displacement is divided into two parts: one is quasi static and the other is dynamic. The quasi-static solution is derived by the state-space method, and the dynamic solution is obtained by the separation-of-variables method coupled with the initial parameter method as well as the orthogonal expansion technique. The present method is suitable for a multilayered orthotropic hollow cylinder consisting of arbitrary layers and subjected to arbitrary axisymmetric thermal loads. Numerical results are finally presented and discussed.     

THERMOELASTIC INTERACTIONS IN A TRANSVERSELY ISOTROPIC ELASTIC MEDIUM WITH A CYLINDRICAL HOLE SUBJECTED TO RAMP-TYPE INCREASE IN BOUNDARY TEMPERATURE OR LOAD

This paper deals with the study of thermoelastic interactions on the basis of the generalized theory of thermoelasticity and with a comparison of the generalized theory of thermoelasticity with the coupled dynamical theory of thermoelasticity for the case of a transversely isotropic elastic medium with a cylindrical cavity when the surface of the cavity is subjected to a ramp-type increase in temperature or load. The solution for the distributions of temperature and stresses are obtained with the help of the Laplace transform technique. Inversions of Laplace transforms are carried out analytically. Discontinuities of the field variables are analyzed. Numerical results for a particular material are also determined in order to extend the problem.     

A TRIBUTE TO IAN NAISMITH SNEDDON: 1919-2000

In this paper we discuss the uniqueness and continuous data dependence questions appropriate to the fundamental initial boundary-value problems in thermoelasticity with one relaxation time. On the basis of the Lagrange identity, we obtain the results for bounded domains as well as for exterior unbounded domains without definiteness conditions on the thermoelastic coefficients other than the positiveness of the product between the thermal conductivity and the relaxation time. The applicability of the Lagrange identity in order to obtain some reciprocal theorems is outlined.     

KIRCHHOFF'S FORMULA FOR THERMOELASTIC SOLID

A generalization of Kirchhoff's theorem for the classical wave equation to the case of a central system of field equations of coupled thermoelasticity is established in this paper. The theorem asserts that a pair (Φ, θ), where Φ and θ denote the thermoelastic displacement potential and temperature, respectively, can be expressed by surface integrals over the boundary of a thermoelastic solid whose kernels have the form of an infinite series satisfying the wave-like and heat-like equations occurring in the decomposition theorem for the central system of equations ([3]).     

HIGH TEMPERATURE THERMOMECHANICAL ANALYSIS OF CERAMIC COATINGS

This paper investigates the thermomechanicai response of ceramically coated metal parts in elevated thermal environments. This is made possible through the development of an improved finite element algorithm that enables the efficient and stable solution of the inherently nonlinear elastic-creep (inelastic) type thermomechanicai field equations associated with high temperature. Based on the improved algorithm, the results of several numerical experiments are presented. These illustrate the significant influence of inelastic behavior in generating residual stress fields.     

DYNAMIC FRACTURE OF TRANSVERSELY ISOTROPIC COUPLED THERMOELASTIC SOLIDS: WEDGING BY A CYLINDER WITH FRICTION

A cylinder of infinite length is introduced in a semi-infinite closed slit in a transversely isotropic solid. Translation toward the slit edge produces mode I crack extension in plane strain. Translation is resisted by cylinder/crack friction, and the crack closes in the wake of the cylinder. A dynamic steady state governed by coupled thermoelasticity ensues in which crack edge and cylinder move at the same constant subcritical speed. The problem has features of both sliding contact and fracture, and robust asymptotic results give solutions that are analytic and—given anisotropy and thermoelasticity—simple in form. Calculations for zinc and a circular cylinder show the effects of cylinder speed and friction on aspects such as temperature change, crack closure compression, and fracture energy release rate.     

Quasi-Static Thermal Stresses Due to Heat Generation in a Thin Hollow Circular Disk

The present paper deals with the determination of displacement and thermal stresses in a thin hollow circular disk defined by a ≤ r ≤ b due to internal heat generation within it. Time dependent heat flux Q(t) is applied at the outer circular boundary (r = b), whereas inner circular boundary (r = a) is at zero heat flux. Also, initially the circular disk is at arbitrary temperature F(r). The governing heat conduction equation has been solved by the method of integral transform technique. The radial stress function σ_rr is zero at inner and outer circular boundaries (r = a and r = b). The results are obtained in a series form in terms of Bessel's functions. The results for displacement and stresses have been computed numerically and illustrated graphically.     

THERMOELASTIC PROBLEM OF UNIFORM HEAT FLOW DISTURBED BY A FLAT TOROIDAL CRACK IN A TRANSVERSELY ISOTROPIC MEDIUM

The thermoelastic problem of uniform heat flow disturbed by a flat toroidal crack in a transversely isotropic medium is investigated using the method of Hankel transforms. The three-part mixed thermoelastic boundary conditions are satisfied using the tech niques of triple integral equations and multiplying factors. The stress intensity factors at the inner and outer crack tips are obtained in exact expressions as the products of a dimensional quantity and nondimensional functions. The fracture transition of a flat toroidal crack to a penny-shaped crack and to a two-dimensional line crack is studied at different values of the ratio of the inner crack radius to the outer crack radius.     

THERMOELASTIC INTERACTIONS WITHOUT ENERGY DISSIPATION IN AN UNBOUNDED MEDIUM WITH A SPHERICAL CAVITY DUE TO A THERMAL SHOCK AT THE BOUNDARY

Thermoelastic interactions without energy dissipation in an unbounded elastic medium with a spherical cavity have been investigated. The cavity surface is assumed to be stress free and is subjected to a thermal shock. The solutions for displacement, temperature, and stresses are obtained using the Laplace transform procedure. The discontinuities of the distributions of the physical quantities are determined and compared with earlier findings. The inversions are also carried out with a numerical method based on Fourier series expansions of functions. The results are compared with the corresponding results obtained in cases of conventional thermoelasticity theory and the generalized theories of thermoelasticity with thermal relaxation time parameters.     

Reconstruction of thermal conductivity and heat capacity using a tomographic approach

We consider the estimation of the volumetric heat capacity and the thermal conductivity as distributed parameters. The measurement scheme consists of sequentially heating the boundary of the object in different source locations and measuring the induced temperature evolutions in different measurement locations on the boundary. The estimation of the distributions of volumetric heat capacity and thermal conductivity based on these boundary data is an ill-posed inverse boundary value problem. We propose an approach which is based on transient data on the boundary and the modelling of the unknown coefficients as Markov random fields. The intended applications are non-destructive retrieval of defects as well as the estimation of macroscopic characteristics of novel materials. We evaluate the proposed approach by a numerical simulation.     

THE CIRCULAR PLATE ON ELASTIC FOUNDATION UNDER TEMPERATURE LOADING

The influence of a quasi-stationary temperature field on the stress state of a thin plate on an elastic half-space is analyzed. A numerical method based on the finite-difference method is derived with regard to the contact stresses, including the shear stresses in the interface between the plate and the subgrade. The special case of central symmetrically loaded plates is considered.     

THERMAL STRESS-FOCUSING EFFECT IN A TRANSVERSELY ISOTROPIC SPHERICAL ZIRCONIA INCLUSION IN AN INFINITE ELASTIC MEDIUM CAUSED BY IMPACT COOLING

When an isotropic infinite elastic medium with a transversely isotropic spherical zirconia inclusion is suddenly subjected to a uniform temperature fall, stresswavesoccur at the interface of the spherical inclusion the moment thermal impact is applied. The stress wave in a transversely isotropic spherical inclusion proceeds radially inward to the center of the inclusion. The wave may accumulate at the center and cause very large stress magnitudes, even though the initial thermal stress should be relatively small. This phenomenon is called the stress-focusing effect. The stress wave in an inclusion may be affected by phase transformation during the tempering process. The stress-focusing effects are analyzed in an exact manner, and a clear indication of the mechanism of thermal and phase transformational stress-focusing effects in a transversely isotropic spherical Zirconia inclusion in the isotropic infinite elastic domain is given.     

新型低温固体氧化物燃料电池研究进展

综述了近年来低温固体氧化物燃料电池(LTSOFC)的研究进展。分别介绍了氧离子传导型LTSOFC、质子传导型LTSOFC以及氧离子质子共传导型LTSOFC的工作原理、关键电池材料(电解质、电极)和电池制备技术的研究现状和发展趋势，并指出了目前存在的问题。     

Estimation of thermophysical properties of fouling using inverse problem and its impact on heat transfer efficiency

At high temperature, the circulation of fluid in heat exchangers provides a tendency for fouling accumulation to take place on the internal surface of tubes. In brief, the deposits on heat exchanger tubes are caused by the presence of inorganic salts, of small quantities of organic materials and products of corrosion in the water. From thermophysical point of view, the deposited fouling has harmful effects on the heat exchanger efficiency. Indeed, it increases the thermal resistance which can raise the energy consumption. This study shows an experimental and a theoretical process of estimation of thermophysical properties of the fouling deposited on a section of a heat exchanger and its effects on the heat transfer efficiency. The estimation method is based on the Gauss-Newton algorithm that minimizes the ordinary least squares function comparing a measured temperature and a theoretical one. The temperature response is measured on the rear face of a bi-layer system composed of a section of a heat exchanger and the fouling deposited on during and after a finite width pulse heat flux on its front face. The theoretical temperature, that is a function of the unknown thermophysical properties of the bi-layer system, is calculated by the resolution of the one-dimensional linear inverse conduction problem, and by the use of the quadrupole formalism.The results of the estimation procedure show, on the one hand the efficiency and the stability of the optimization algorithm to estimate the thermophysical properties of the fouling. On the other hand they underline the necessity of the maintenance of fluid circulating tubes at high temperature.     

Estimation of thermal contact resistance and temperature distributions in the pad/disc tribosystem

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent thermal contact resistance for the tribosystem consisting of a semi-infinite foundation (disc) and a plane-parallel strip (pad) sliding over its surface, from the knowledge of temperature measurements taken within the foundation. Subsequently, the temperature distributions in the medium can be determined as well. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the measurement errors upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent thermal contact resistance can be obtained for the test case considered in this study. The current methodology can be applied to the prediction of thermal contact resistance in engineering problems involving sliding-contact elements.