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‣ The deformation of cylindrical shells subjected to radial loads

Madureira, M.L.R.; Fonseca, E.M.M.; Melo, F.J.M.Q. de
Fonte: Universidade de São Paulo Publicador: Universidade de São Paulo
Tipo: Conferência ou Objeto de Conferência
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Cylindrical shells have a simple geometry and application in pressure vessels and piping engineering. The development of calculation algorithms in structural project is impelled by a constant challenge in the search of more accurate and fast design tools in engineering. The objective of this work is to contribute with a simple and reliable numerical tool for the stress analysis of cylindrical vessels subjected to generalized forces. A hybrid formulation in the definition of forces and displacements is proposed for cylindrical shells subjected to radial loads. Variational techniques coupled with functional analysis are used to obtain an optimized solution for the shell displacement and further stress field evaluation. As it is not possible to obtain exact solutions for the displacements or deformation field whenever the external loads are either concentrate or locally distributed, the solution here proposed deals with the combination of unknown analytic functions combined with Fourier expansions, where the former depend on the axial shell coordinate and the trigonometric terms are dependent upon the cylinder circumferential polar angle. These functions are expanded in Fourier series where displacement amplitudes are combined with trigonometric terms. The result is a system of ordinary differential equations where the solution is analytic after evaluation of eigenvalues and eigenvectors. The boundary conditions are then used to reach the final solution. As an example a large cylindrical shell subjected to pinching loads is considered. The results for the radial displacement and section ovalization are analyzed where the solution was obtained with three terms (nq=6) for the accuracy is acceptable in this case. The transverse displacement presents important dependence on the shell thickness vs radius...

‣ Análise numérica e experimental da ação do vento em estruturas em cascas de formas livres; Numerical and experimental analysis of wind action on structures in shells freeforms

Antônio Mário Ferreira
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/12/2013 Português
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Este trabalho realiza uma análise numérica e experimental do comportamento de estruturas em cascas de formas livres sob a ação do vento. Inicialmente foram gerados modelos computacionais de formas otimizadas, sendo uma casca de planta pentagonal e outra hexagonal. Na sequência foram construídos modelos físicos reduzidos em laboratório e submetidos a uma série de ensaios em túnel de vento. E, finalmente foram realizadas simulações numéricas dessas estruturas submetidas à ação do vento utilizando o programa computacional ANSYS-CFX do Laboratório de Informática da FEC-UNICAMP. Os modelos físicos reduzidos analisados foram gerados utilizando o software ANSYS e o programa computacional desenvolvido por Vizotto (1993), e construídos no Laboratório de Automação e Prototipagem para Arquitetura e Construção (LaPAC) da FEC-UNICAMP, utilizando inicialmente isopor de alta densidade, que foi posteriormente empregado para execução de fôrmas de concreto armado para moldar os modelos finais em material composto por fibra de vidro e resina, para serem ensaiados no túnel de vento do Laboratório de Conforto Ambiental e Física Aplicada (LaCAF) da FEC-UNICAMP. Os testes no túnel de vento do LaCAF foram realizados em dezesseis fases...

‣ Knockdown Factors for Buckling of Cylindrical and Spherical Shells Subject to Reduced Biaxial Membrane Stress

Hutchinson, John W.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Cylindrical shells under uniaxial compression and spherical shells under equi-biaxial compression display the most extreme buckling sensitivity to imperfections. In engineering practice, the reduction of load carrying capacity due to imperfections is usually addressed by use of a knockdown factor to lower the critical buckling stress estimated or computed without accounting for imperfections. For thin elastic cylindrical shells under uniaxial compression and spherical shells under equi-biaxial compression, the knockdown factor is typically as small as 0.2. This paper explores the alleviation of imperfection-sensitivity for loadings with a reduced circumferential (transverse) membrane stress component. The analysis of Koiter (1963) on the effect of an axisymmetric imperfection on the elastic buckling of a cylindrical shell under uniaxial compression is extended to both cylinders and spheres for loadings that produce general combinations of biaxial membrane stresses. Increases in the knockdown factor due to a reduction of the transverse membrane component are remarkably similar for cylindrical and spherical shells.; Engineering and Applied Sciences

‣ Creep buckling of spherical shells.

Xirouchakis, Paul Christos
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 391 leaves; 13961993 bytes; 13961752 bytes; application/pdf; application/pdf
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Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Ocean Engineering.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Includes bibliographical references.

‣ On finite element nonlinear analysis of general shell structures.

Bolourchi, Said
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 179 leaves; 9917003 bytes; 9916759 bytes; application/pdf; application/pdf
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1979.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Vita.; Includes bibliographical references.

‣ On triangular finite elements for general shell structures

Lee, Phill-Seung, 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 162 leaves; 7818925 bytes; 7839613 bytes; application/pdf; application/pdf
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In general, triangular elements are most efficient to discretize arbitrary shell geometries. However, in shell finite element analysis, usually quadrilateral elements are used due to their better performance. Indeed, there does not exist yet a "uniformly optimal" triangular shell element. The work in this thesis focuses on the development of continuum mechanics based triangular shell elements (of low and high order) which overcome the known disadvantages and show uniform optimal convergence. As the shell thickness decreases, the behavior of shell structures falls into one of three categories (bending dominated, membrane dominated or mixed problems) depending on the shell geometry and the boundary conditions. We develop a numerical scheme to evaluate the behavior of shells and perform the asymptotic analysis of three shell structures. We also present the asymptotic analysis results of a highly sensitive shell problem which has a fluctuating load-scaling factor. These results provide basic information for effective numerical tests of shell finite elements. We develop a new systematic procedure for the strain interpolation of MITC triangular shell finite elements that results into spatially isotropic elements. We propose possible strain interpolations and develop five new specific triangular shell finite elements. Considering the asymptotic behavior of shells...

‣ Commercial application of aluminum honeycomb and foam in load bearing tubular structures

Bartolucci, Stefano, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 leaves; 8319626 bytes; 8340736 bytes; application/pdf; application/pdf
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Small dimension engineering tubular structures subjected to a complex load system are designed like hollow circular shells. For minimum weight design, the ratio between the shell radius and the thickness has to be as large as possible, but its maximum value is limited by the onset of local buckling. Tubular natural structures subjected to a complex load system have often an outer shell of solid material supported by a low density, compliant core, which makes them more resistant to local buckling. Biomimicking of natural constructions offer the potential to improve the design of small diameter tubular engineering structures. Here, the fabrication technology of biomimicked engineering tubular structures integrating aluminum foam or honeycomb as core material is discussed. A viability analysis is presented including technical performance, cost, utility, and risk assessments. Aluminum compliant core shells have potential for substituting CFRP and aluminum tubular structures in aerospace and high-level sport applications. The case of sailboat masts was considered in detail. Results of our analysis proved that use of honeycomb as core material can lead to a significant reduction of the mast weight. Business opportunities based on this application are discussed.; by Stefano Bartolucci.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Finite element analysis of shells with layers

Hiller, Jean-François, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 169 leaves; 6643510 bytes; 6643319 bytes; application/pdf; application/pdf
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It is well established that thin shell structures frequently feature narrow bands of strain concentration and localized displacement irregularities referred to as boundary and internal layers. It is crucial to capture these layers properly as they can be sources of structural failures. Unfortunately, while the absence of analytical solutions to most shell problems of practical interest has spawned the development of a variety of finite element formulations over the years, largely speaking these schemes were proposed without a rigorous and comprehensive testing procedure available. We are now faced with a wealth of existing formulations and little way to assess their ability to model boundary and internal layers. Most of the difficulties in assessing the performance of shell finite elements stem from the use of mixed formulations. These are necessary to alleviate the locking phenomenon present in bending-dominated problems when displacement-based formulations are used. We develop a new error measure approach that is physically-based and can be used to assess the performance of mixed-interpolated shell finite element formulations. We apply this approach to the MITC (Mixed Interpolation of Tensorial Components) family of shell elements...

‣ Scattering from sub-critically insonified buried elastic shells

Lucifredi, Irena
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 217 p.; 10275853 bytes; 10285045 bytes; application/pdf; application/pdf
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Buried mines have been so far generally considered undetectable by conventional high frequency sonars mostly due to the low levels of energy penetrating into the sediment at high frequencies. Furthermore, in a shallow water environment a high frequency high grazing angle mine-hunting sonar approach is vastly limited by the coverage rate, making the detection and classification of buried objects using subcritical grazing incidence an attractive alternative. In mine countermeasurements (MCM) applications resonance of man-made elastic targets is a pivotal concept that distinguishes them from rocks or other clutter that may have a similar mine-like shape. Nevertheless, burial of an elastic target in the seabed results in a variety of modifications to the scattered response caused by different physical mechanisms, geometric constrains, and intrinsic properties of the sediment. The goal of this thesis was to identify, analyze and explain the fundamental effects of the outer sediment and the proximity of the seabed interface on the scattering of sound from elastic shells insonified using low frequencies at subcritical incident angles.; (cont.) The approach to scattering from buried elastic shells consisted of the development and the evaluation of ways of computing the scattered field...

‣ Development of a co-dispersion binder for the three-dimensional printing process to facilitate handling of ceramic casting shells in the green state

Yu, Richard Li-Chao
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 136 leaves
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by Richard Li-Chao Yu.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994.; Includes bibliographical references (leaf 107).

‣ Sintering and joining of low temperature co-fired tungsten and aluminum oxide

Boonyongmaneerat, Yuttanant
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 189 p.
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Conventional methods used to fabricate co-fired tungsten/alumina composites usually rely on high temperature processing (>1500C). As it would be beneficial or even necessary for some applications to produce such composites at relatively low firing temperatures, low-temperature processing techniques and the attendant knowledge of processing-property relationships need to be developed. In this thesis, a set of experiments and simulations are performed to obtain a better understanding of sintering and joining of the tungsten/alumina system processed at temperatures near or below 12000C. The technique of activated sintering for tungsten is investigated, whereby a minimal content of additives enables low firing temperatures through a change in the sintering mechanism for tungsten. Tungsten compacts produced by this method are found to sinter only to the "initial stage" and are characterized by high residual porosity level. Hardness and fracture toughness of such partially-sintered materials are examined experimentally and analytically, and dependence of mechanical properties on the relative particle neck size is observed. Various studies are carried out to examine both fundamental and practical aspects of joining co-fired tungsten/alumina.; (cont.) First...

‣ 2.081J / 16.230J Plates and Shells, Spring 2006; Plates and Shells

Wierzbicki, Tomasz
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
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This course explores the following topics: derivation of elastic and plastic stress-strain relations for plate and shell elements; the bending and buckling of rectangular plates; nonlinear geometric effects; post-buckling and ultimate strength of cold formed sections and typical stiffened panels used in naval architecture; the general theory of elastic shells and axisymmetric shells; buckling, crushing and bending strength of cylindrical shells with application to offshore structures; and the application to crashworthiness of vehicles and explosive and impact loading of structures. The class is taught during first half of term.

‣ Dielectrophoresis-based double-emulsion droplet centering for concentric laser target foam shells

Bei, Zongmin (1981 - ); Jones, T. B. (1944 - )
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xxxvii, 213 p.
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Thesis (Ph. D.)--University of Rochester. Dept. of Mechanical Engineering, 2011.
"Appendix A was provided by Professor Masao Washizu, University of Tokyo. Appendix E was provided by Wade Bittle, Laboratory for Laser Energetics, at the University of Rochester."--P. 1; Cryogenic laser targets used for inertial confinement fusion experiments are prepared from hollow, low-density polymer foam shells. For effective implosion, these foam shells must meet very rigid requirements on their dimensions. They must be concentric within ≤5% of the average shell thickness and the inner surface root-mean-square (RMS) roughness must be on the scale of microns. In this dissertation, a voltage-controlled scheme for centering double-emulsion droplets is developed based on dielectrophoresis (DEP). This technique has potential application in a scalable microfluidic assembly-line process for the formation of highly concentric foam shells for laser targets. The DEP centering effect, utilizing a uniform AC electric field, originates from the interactions between the induced dipoles of the inner droplet and the surrounding liquid. Double-emulsion droplets can be centered only when the dielectric constant of the outer shell is higher than that of the suspension medium. The dielectric constant of the inner droplet has no effect on the centering stability. The AC frequency of the applied electric field must be sufficiently high (~20 MHz) to overcome electrostatic shielding due to the electrical conductivity (>10-3 S/m) of the liquid forming the outer shell. To minimize gravity and buoyancy...

‣ Comparison of analytical and numerical approaches for determining failure of ring-stiffened cylindrical shells

Temme, Michael W.
Fonte: Cambridge, Massachusetts, Massachusetts Institute of Technology Publicador: Cambridge, Massachusetts, Massachusetts Institute of Technology
Tipo: Tese de Doutorado
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CIVINS; The thesis compares the analytical solution, two marine classification society design rules, and numerical analysis against experimental results for predicting the failure modes (general instability, axisymmetric buckling, and asymmetric collapse of the shell) and failure pressures of ring-stiffened cylindrical shells. The analytical solution is first summarized based on several sources. Design rules for the classification societies are then presented with brief explanations for each one. The design rules used are: American Petroleum Institute (Bulletin on Stability Design of Cylindrical Shells, API Bulletin 2U, Second Edition, October 2000) and Det Norske Veritas (Buckling Strength of Shells, Analysis Evaulation and Structural Optimization (MAESTROtm, version 8.5, Proteus Engineering) The United States Navy Naval Sea Systems Command, Submarine Structural Integrity Division supplied experimental data for four test cylinders that covered the failure modes and allowed comparison between experimental and analytical / numerical results. The comparison of experimental to predicted data found the design rules and numerical solution performed adequately in predicting asymmetric buckling and general instability failure modes, but the predictions for failure pressure were unsatisfactory. The design rules were overly conservative in their predictions of failure pressure due to the semi-empirical solutions used in the rules. The numerical solution was only slightly better for the same failure pressure predictions. The results indicate the predicted failure pressure for a cylinder is closely tied to the size and dimensions of the cylinders used for determining the empirical solutions. These results should be further explored to determine causes and corrections.

‣ Tecnología para la construcción de cubiertas doblemente curvadas a partir de elementos planos; Technology to build double curved shells from plane elements

Martín-Oar Luca de Tena, Rocío
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis Formato: application/pdf
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Arquitectos e ingenieros buscan constantemente nuevas soluciones para la creación de espacios envolventes eficientes. La industrialización y el desarrollo del mundo moderno han estimulado inevitablemente la demanda de cubiertas eficientes y capaces de encerrar grandes áreas libres de columnas. Las estructuras espaciales, sin duda, satisfacen dicha demanda y, si son bien diseñadas, requieren un uso mínimo de materiales estructurales. Este proyecto presenta un estudio sobre una nueva tecnología para construir cubiertas de doble curvatura a partir de elementos planos. Este trabajo se ha llevado a cabo en el Instituto de Ingeniería Estructural de la Universidad Tecnológica de Viena, bajo la dirección de O.Univ.Prof. Dipl.-Ing. Dr.-Ing. Johann Kollegger, y la supervisión de Dipl.Ing. Sonja Dallinger. Este nuevo método de construcción consiste en la transformación de un plato plano, formado por elementos, en una cubierta semiesférica mediante el uso combinado de elementos prefabricados, cables tensionados y un globo neumático. Además, este método no sólo es adecuado para cubiertas de hormigón, sino también para cubiertas de hielo. Diferentes experimentos se han realizado en el Instituto desde el 2005. Las cubiertas delgadas de hormigón son duraderas y demandan un mantenimiento mínimo. Este nuevo sistema mantiene todas las ventajas de las cubiertas de hormigón...

‣ Construction method to build ice shells with pneumatic formwork; Método de construcción de cúpulas de hielo a partir de reforma plástica neumática

Pérez Latorre, Juan Ignacio
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis Formato: application/octet-stream; application/octet-stream; application/pdf; application/pdf
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This thesis has presented a study into the new construction method to build ice shells with pneumatic formwork, developed at the Institute for Structural Engineering of the Vienna University of Technology. Shells are natural, logical and functional load carrying systems. Additionally, for the load transfer of a uniformly distributed load, the shell structure is the perfect choice because mainly normal forces appear in the cross section. Although shell structures possess excellent load carrying system and make a great visual impact, only few shells have been built in the last decades. The main problem is the difficult, time-consuming and expensive production. Traditionally, shells are produced by means of complex formwork. Creating such formwork increases the construction time and affords additional material which cannot be reused after the shell has been completed. Ice as a construction material is either used as a decorative material on a supporting structure or it is applied in structures with very low stress states due to self weight and wind forces. Ice shells can be used in temporary architecture, as roof structures for sport and music events, or presentations and promotions of sale products. Moreover the translucent nature of ice...

‣ Computation of acoustic scattering from elastic conical shells with endcaps using the hybrid finite element/ virtual source approach

Low, Hwee Min Charles
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 174 p.; 6303584 bytes; 6310885 bytes; application/pdf; application/pdf
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Studying and understanding acoustic scattering pattern from underwater targets has been of interest to various communities such as the archeologists and the navy for several reasons and applications. The present state-of-the-art technique in this area involves such methods as analytical approach and FEM/BEM numerical technique. This thesis aims to study and demonstrate the power of using the hybrid virtual source/FE approach where the physical presence of a target is replaced by virtual sources placed in the vicinity of the target and in a manner where the pressure/displacement relationship on the target surface is satisfied by the virtual sources when the target is being insonified. Accurate results for the far-field radiation of the target can be obtained by superposition of the point source Green's function of each virtual source. The hybrid virtual source/FE approach shows potential to be a computationally efficient method for computing acoustic scattering. The derivation of the dynamic flexibility matrix for an elastic conical shell with endcaps will be illustrated in this thesis. It will be shown that the dynamic flexibility matrix corresponds to the acoustic admittance matrix in the virtual source approach where the scattering functions are computed in the MIT's program OASES/SCATT.; (cont.) Moreover...

‣ Past and future of grid shell structures

Paoli, Céline (Céline Aude)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves
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Because of their original organic shape and the column free space that they provide, the design of grid shell structures challenges architects and structural engineers in more than one way. Very few grid shell building exist around the world. This scarcity may be explained by the level of innovation required in such fields as design technique; construction scheme, use of material... The goal of this paper is to unify the design work done on grid shells, to understand the evolution of the designs and to provide the reader with a sense of what awaits grid shell structures in the future. The construction of a timber grid shell starts from a flat, two dimensional wooden net, the three dimensional shell type structure is then achieved by pushing on the edges of this mat and gradually releasing the internal stresses at the joints to enable the shape to live and the structure to take its most adequate form. Only three wooden grid-shell structures exist world wide, by studying the way they work and behave, as well as the process that lead to the choice of such a structure, we'll understand how grid shell were born in the mind of architects and structural engineers.; (cont.) Even if the mechanism of grid shells is a very clever and well thought system...

‣ A study of the dynamics of shells with boundary layers and a study of the MITC3 shell element; Study of the MITC3 shell element

Malek, Samar R. (Samar Rula)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves
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Shell structures are frequently used for their aesthetic appeal, and material efficiency. They can be found everywhere, in all sorts of contexts. For example, they can serve as roofs to encapsulate large areas (think Millennium Park in Chicago); as fuselage for an airplane; as the frame of a car; as chemical containers (such as pressure vessels); even submarines. One of the most challenging phenomena in shells is boundary layers. Boundary layers are high concentrations of energy due to either irregular loadings, or incompatible boundary conditions, or geometric discontinuities. Previous studies have determined the location of this concentrated energy and how that location varies depending on the thickness of the shell; up to now however, any correlation between the boundary layers and the vibrations of the shell has not yet been examined. In our first study, we review the boundary layer behavior, and we investigate the dependence of the shell's natural frequencies on the boundary layer phenomenon for two shell benchmark problems: the Scordelis-Lo Roof and the Clamped Hyperboloid.; (cont.) In our second study, we shortly review the MITC3 shell element. This element is known to lock in plate bending cases for a specific mesh pattern. Finally...

‣ Thermal stresses in closed spherical shells

Keene, Frank W.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
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The purpose of this work is to discuss thermal stresses in closed spherical shells. This effort is further limited to linear thermoelastic stresses in "thin" shells. The basic concepts associated with three-dimensional continuum mechanics are presented in both direct and general tensor notation. The three-dimensional equations are reduced to the two-dimensional equations of shells under going finite displacements. These are subsequently reduced to those pertaining to spherical shells. A review of the recent literature associated with thermal stresses in spherical shells is included. An appendix is provided which reviews some of the basic elements of general tensors.