CYCLIC LOADING OF THERMAL STRESSES

The isotropic and kinematic hardening theories of plasticity are used to evaluate the cyclic loading behavior of structures under thermal stresses. The material of the structures used in this article is assumed to follow nonlinear strain hardening property. The material's strain hardening curve in tension and compression is assumed to be both identical for isotropic material and different for anisotropic material. The method of successive approximation is used to calculate the stresses and plastic strains in the structure due to cyclic loadings. The results of the analysis are checked with the known experimental test. The thermal stresses are categorized into load- and deformation-controlled stresses. It is concluded that the isotropic hardening theory, excluding creep, will always result in structural shakedown. The kinematic hardening theory under deformation-controlled conditions, excluding creep, will result in reversed plasticity. The load-controlled cyclic loading under kinematic hardening theory with isotropy assumption results in reversed plasticity. Under the anisotropy assumption of tension/compression curve, the load-controlled stress based on kinematic hardening theory predicts ratcheting behavior. When creep deformation is considered, the load-controlled thermal stresses results in ratcheting, and the deformation-controlled thermal stresses result in shakedown behavior, regardless of the material's isotropic and anisotropic properties or the hardening theories.     

THERMAL BUCKLING ANALYSIS OF ISOTROPIC AND COMPOSITE PLATES WITH A HOLE

Abstract

We analyze thermal buckling of both circular isotropic plates and square antisymmetric angle-ply laminates with a hole in the middle, and subject to a uniform temperature rise, by either closed form solution for the former or finite-element method for the latter. Thin-plate theory is used to analyze the isotropic plates. However, a high-order displacement theory including high-order terms along the transverse direction taking into account transverse normal strain is used in the case of laminates. Results for the isotropic plates indicate that in contrast to the reduction in mechanical buckling loads due to the hole, the thermal buckling temperature actually rises as the size of the hole increases, which indicates that the effect on stress reduction exceeds that on stiffness decrease. Results are more complicated for laminated plates, due to anisotropy.     

THERMOELASTIC DEFORMATION OF MICROSTRETCH ELASTIC BEAMS

This article addresses the problem of thermal stresses for isotropic microstretch elastic cylinders subjected to a temperature distribution that is linear in the axial coordinate. A direct method is used to reduce the problem to solving plane strain problems. The results are used to study the deformation of circular cylinders.     

SIMULATED EFFECTIVE THERMAL CONDUCTIVITY OF SINTERED,RANDOMLY PACKED SPHERES AND STATISTICAL STRUCTURES OF PACKINGS

Effective thermal conductivity of sintered spherical particles is estimated by a computer simulation. The simulation consists of (i)simulated random packing of equal spheres by a method of "rigid sphere free fall into a virtual box," (ii) finite element method (FEM) estimation of the thermal resistance of a "sintered" pair of spheres, and (iii) simulated heat conduction tests of a "random network," as a model of sintered particles, of thermal resistors with the estimated resistance; these tests yield the effective conductivity of sintered spherical particle aggregates. Statistical structures of the random packings of spheres are examined. The random packings constructed are standard "loose random packings." The cumulative diameter distribution of circles appearing on cross-sections of the packings is in complete agreement with the theoretical prediction for all three orthogonal directions, implying that the packing structures are isotropic. And, despite this result, the zenithal distribution of branch orientations deviates from a uniform one; more spheres are in contact with their neighbors at the zenithal angles of theta approxequal 45 degrees. The effective conductivities obtained are not isotropic but transversely isotropic, which is due to the deviation of branch orientations.     

一种新型大尺寸多晶硅片晶向的光学扫描方法

提出了一种新型扫描大尺寸多晶硅片晶向的方法,该方法以晶粒表面光学3D各向形貌的分析为基础,通过2部相机直接采集得到晶粒的2D反射谱;每种不同晶向有其特定的表面形貌及对应的特征反射谱线,该特征反射谱线由理论推测而得,并与实验结果相符;晶粒的晶向指数可以由特征谱线峰值计算得出。本测试实现了对100×100 mm^2碱制绒硅片的晶向检测,测试时间小于10 min,检测精度小于1.34°。这种快速扫描晶向的方法可以用于高效多晶硅片的研发。     

OPTIMUM DESIGN OF A MULTILAYERED COMPOSITE PLATE USING NEURAL NETWORKS

An approximate optimum design of a multilayered composite plate constructed of an isotropic structural layer and multiple piezoceramic layers is presented. A thermoelastic displacement distribution on the structural layer surface is controlled by applying appropriate electric potential distributions to the piezoceramic layers. The objective of this study is to determine the thickness of each piezoceramic layer by using neural networks so that the maximum value of the applied electric potential distributions is minimized subject to stress constraints. The quasi-Newton method is employed for an updating formula of connection weights. Numerical results for the approximate optimum design of the composite plate are shown to be in good agreement with those obtained from a direct optimum design using the quasi-Newton method.     

APPLICATION OF TAYLOR TRANSFORMATION TO THE THERMAL STRESSES IN ISOTROPIC ANNULAR FINS

This article presents the stresses distribution in a perfectly elastic isotropic annular fin. The Taylor transformation method is used to solve the nonlinear temperature field equation. The stresses distribution are integrated obtain the results. The thickness of the fins is assumed to be sufficiently small so as to have a state of plane stress and one-dimensional heat conduction.     

A POD-Galerkin reduced-order model for isotropic viscoelastic turbulent flow

In this article, a proper orthogonal decomposition (POD) reduced-order model for isotropic turbulent flow of viscoelastic fluid is established for the first time. Particularly, since the present studies about viscoleastic fluid are mainly for revealing the mechanism of turbulence, we try to establish the reduced-order model for momentum equations and constitutive equations, finally get both velocities and deformation rates calculated. Through decomposing the sampling matrices which are obtained by direct numerical simulation (DNS) using finite volume method (FVM), the velocity basis functions and deformation rate basis functions are generated respectively. According to the Galerkin projection method, the equations for velocity spectrum coefficients and deformation rate spectrum coefficients are deducted, which are coupled pluralistic nonlinear equations and solved iteratively by the Newton–Raphson method. To illustrate the performance of the proposed model for the viscoelastic fluid flow, a two-dimensional decaying isotropic turbulence testing case is designed in Example 1. It is found that the established reduced-order model obtains good accuracy when the decaying flow is at its early stage, but the errors get considerable when the flow steps into transition flow. In addition, a three-dimensional forced isotropic viscoelastic turbulence testing case is designed in Example 2. It is indicated that the errors of viscoelastic forced isotropic turbulent flow are acceptable. Finally, the calculation speed of the established reduced-order model is found to be much faster than that of DNS.     

A THEORY OF THERMOVISCOELASTIC DIELECTRICS

We study finite deformations of heat conducting viscous dielectric solids and derive constitutive relations that satisfy an entropy inequality. These are simplified for orthotopic, transversely isotropic, and isotropic materials. For each class of materials, linear constitutive relations valid for infinitesimal deformations are derived.     

Study of the effective parameters on stress distribution around triangular hole in metallic plates subjected to uniform heat flux

On the basis of the steady-state two-dimensional theory of thermoelasticity, stress field around a triangular hole in an infinite isotropic plate is discussed. A metallic plate subjected to uniform heat flux and thermal-insulated condition along the hole boundary is assumed. The method used for this study is the expansion of Goodier and Florence's method. They used the complex variable method for stress analysis of infinite isotropic plates with an elliptical or circular hole. The rotation angle of the hole, bluntness, aspect ratio of hole size, and angle of heat flux are important parameters considered in this paper.     

Transient Piezothermoelasticity of a Two-Layered Composite Hollow Cylinder Constructed of Isotropic Elastic and Piezoelectric Layers Due to Asymmetrical Heating

This article is concerned with the theoretical treatment of transient piezothermoelastic problem involving a two-layered hollow cylinder constructed of isotropic elastic and piezoelectric layers due to asymmetrical heat supply. The transient two-dimensional temperature is analyzed by the method of Laplace transformation. By using the exact solutions for piezoelectric hollow cylinder and isotropic hollow cylinder, the theoretical analysis of transient piezothermoelasticity is developed for a two-layered composite hollow cylinder under the state of plane strain. As an example, numerical calculations are carried out for an isotropic elastic hollow cylinder made of steel, bonded to a piezoelectric layer of cadmium selenide. Some numerical results for the temperature change, the stress and the electric potential distributions in a transient state are shown in figures. Furthermore, the influence of thickness of the piezoelectric layer or the isotropic elastic layer upon the temperature change, stresses and electric potential is investigated.     

THERMOELASTIC STRESS OF MULTILAYER CYLINDRICAL BODIES

An effective solution of the boundary value and boundary contact problems of thermal stress of elastic one- and multilayer bodies bounded by the coordinate surfaces of generalized cylindrical coordinates 𝜌 , f , z ( 𝜌 , f are orthogonal curvilinear coordinates on the plane and z is a linear coordinate) is given. The body occupies the domain z = { 𝜌 0 < 𝜌 < 𝜌 1 , f 0 < f < f 1 , 0 < z < z 1 } ; and a thermal disturbance is defined on the free of stress planar parts z = 0 and z = z 1 of the boundary surface, while homogeneous conditions of either symmetry or antisymmetry type are given for the remaining part of the boundary. The elastic body is assumed to be nonhomogeneous along z and transversally isotropic with the plane of isotropy z = const . The transversally isotropic layers of the multilayer body make contact along the planes z = const .     

APPLICATION OF THE FIVE-ELEMENTARY-FUNCTIONS METHOD TO TRANSIENT THERMAL-STRESS PROBLEMS IN MULTIPLY CONNECTED ORTHOTROPIC REGIONS

In a previous paper, we dealt with transient, plane, thermoelastic problems in a multiply connected isotropic region using the five-elementary-functions method. As an extension of this method to orthotropic bodies, this paper is concerned with transient, plane, thermal-stress problems in multiply connected orthotropic regions.     

塔式太阳能集热器HTF温度均化特性研究及评价

以太阳能发电站中集热器中的传热介质(HTF)为研究对象,并对其进行量化评价.采用数值模拟的方法研究3种介质在集热器内的流动和传热特性,流体介质假定为各向同性的均匀介质,液相处于局部热平衡状态,对集热管的轴向切平面和周向截面的温度分布进行分析和定量评价.结果表明,液态钠作为塔式太阳能集热管的传热介质时管壁及管内的温度分布...     

ON THE AXISYMMETRIC PROBLEMS OF GENERALIZED ANISOTROPIC THERMOELASTICITY

In this article a two-dimensional axisymmetric problem in a homogeneous transversely isotropic medium has been studied by employing the eigenvalue approach after applying the technique of Laplace and Hankel transforms. An example of infinite space with concentrated force at the origin has been presented to illustrate the application of the approach. The results for coupled thermoelasticity and in the case of a homogeneous isotropic medium have also been deduced. The results obtained can be used for a broad class of problems in generalized thermoelasticity. The integral transforms have been inverted by using a, numerical technique to obtain the displacements, temperature, and stresses in the physical domain. The results for these quantities are given and illustrated graphically.     

AN APPROXIMATE APPROACH TO NONLINEAR THERMAL BENDING OF SHALLOW SANDWICH SHELLS AND FLAT PLATES

By extending the well-known Berger approach for single-layer isotropic elastic plates, an approximate method of analysis for the nonlinear bending of shallow sandwich shells is proposed. Governing field equations are derived for shallow sandwich shells subjected to mechanical as well as thermal effects. Numerical calculations are carried out for large deflections of shells and flat plates due to a temperature difference between the upper and lower faces, and the applicability of the approximate field equations is discussed.     

INVERSE TRANSIENT THERMOELASTIC PROBLEM FOR A COMPOSITE CIRCULAR DISK

The present article deals with the application of a piezoelectric material as a sensor of thermomechanical disturbance. We consider a composite circular disk constructed of a transversely isotropic layer onto which a piezoceramic layer of crystal class 6mm is perfectly bonded. An inverse transient thermoelastic problem is solved to determine the unknown transient heating temperature distribution on the surface of the transversely isotropic layer, when the distribution of the electric potential difference across the piezoceramic layer is known. A finite difference method with respect to the time variable is employed to solve this inverse problem. The thermoelastic fields in the transversely isotropic and piezoceramic layers are analyzed by means of a transversely isotropic potential function method and a piezothermoelastic potential function method, respectively. Numerical results are presented for the time variation of the inferred heating temperature distribution and the corresponding distributions of temperature, displacements, stresses, and electric displacements.     

ON THE CHARACTERIZATION OF THE MIXED PROBLEM OF COUPLED,DYNAMIC, LINEAR THERMOELASTICITY IN TERMS OF THE TEMPERATURE

The temperature field in the coupled, dynamic theory of linear thermoelasticity for homogeneous and isotropic bodies satisfies a partial differential equation in which the temperature is the only unknown-the so-called temperature equation. Here, for certain classes of problems, appropriate boundary and initial conditions are derived for the temperature equation from the data for the corresponding mixed problem of thermoelasticity. It is shown that the resulting boundary-initial-value problem for the temperature has at most one solution. Furthermore, for these classes of problems, it is shown that a displacement field can be ex pressed directly in terms of the temperature field and that the corresponding thermoelastic process satisfies all of the conditions of the mixed thermoelasticity problem except for the tangential components of the mechanical boundary conditions. To this extent, our boundary-initial-value problem for the temperature uncouples the coupled theory.     

An extension for the Ohno–Wang kinematic hardening rules to incorporate isotropic hardening

In this work, an extension of the well-known Ohno–Wang model to incorporate isotropic hardening is presented and discussed. The model is extended by taking into account isotropic hardening depending on accumulated plastic strain. It is assumed that isotropic hardening will be associated with kinematic hardening in the governing equations where activation of either isotropic or kinematic hardening is controlled through a specific controller parameter κ. The accuracy of simulations can be adjusted by changing the value of this controller parameter. It is shown that such an extension is effective and restrains activation of dynamic recovery resulting in less accumulated ratchetting strain with large values of the controller parameter. In addition, it is shown that the extended model simulates multiaxial ratchetting experiments conducted on SS 304L by Hassan et al. fairly well.     

DERIVATION OF CONSTITUTIVE EQUATIONS FOR IDEAL PLASTIC MATERIAL FROM CLAUSIUS-DUHEM INEQUALITY

The constitutive equations for an ideal plastic material are derived naturally from the Clausius-Duhem inequality and the yield function. An admissible thermodynamic process must satisfy the inequality. If there is no restriction on the stress and temperature rates in the elastic state, then we obtain the elastic constitutive equations. However, if they are related in the yield state by means of the yield criterion, then the constitutive equation may contain a term that corresponds to the plastic flow of the ideal plastic material. The isotropic case is considered, and we obtain Hook's law, the thermal isotropic expansion, and the Levy-St. Venant flow rule.