Thesis. 1978. Sc.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Sc.D.

Στην εργασία αυτή θα πραγματευθούμε προβλήματα με βάση τη γενικευμένη θεωρία των Lord και Shulman και αυτή των Green και Lindsay. / --

Thesis (M.S.)--University of Michigan, 1955.

Orientador: Renato Pavanello / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T18:05:36Z (GMT). No. of bitstreams: 1 QuispeRodriguez_Sergio_M.pdf: 51003475 bytes, checksum: 7e557fe0fe0448fd7cae415ebca527f8 (MD5) Previous issue date: 2015 / Resumo: A otimização estrutural topológica é uma ferramenta aplicada atualmente em muitos campos da engenharia tendo se consolidado no meio acadêmico e industrial. Em muitos casos práticos os carregamentos mecânicos e térmicos ocorrem simultaneamente nas estruturas. Nestas situações, a aplicação do método de otimização estrutural topológica deve contemplar tanto os requisitos mecânicos, como os requisitos térmicos. Assim, uma abordagem multi-física e multi-objetivo precisa ser desenvolvida para a solução desta classe de problemas. O presente trabalho é dedicado ao estudo da aplicação do método BESO (BESO - Bi-directional Evolutionary Structural Optimization) à sistemas multi-físicos considerando inicialmente os carregamentos termo-mecânicos como forças de corpo ou seja, forças dependentes do projeto. As funções objetivo consideradas são a flexibilidade média da estrutura e a capacidade térmica do sistema. A análise termo-mecânica é realizada usando o método de acoplamento sequencial, onde obtêm-se inicialmente a resposta do campo térmico, ou aplica-se um campo previamente conhecido do ponto da estrutura e na sequência calculam-se as forças térmicas geradas e a dilatação da estrutura. Explora-se também a otimização termo-mecânica multiobjetivo, em que duas funções objetivo são consideradas simultaneamente. Considera-se como o objetivo do problema de otimização, a minimização da flexibilidade média e a minimização da capacidade térmica, usando o método de soma ponderada. Para a validação dos procedimentos de otimização implementados neste trabalho, são apresentados exemplos de otimização para sistemas termo-mecânicos bidimensionais. A viabilidade do método para aplicação em problemas de engenharia e a comparação de resultados com outros métodos de otimização, permite afirmar que as técnicas propostas podem ser usadas na solução de problemas de otimização topológica de sistemas termo-mecânicos / Abstract: The structural topology optimization is an usefull tool applied in many engineering fields, having been established in the academic and industrial environments. In many practical cases, the mechanical and thermal loads occur simultaneously in a structure. In these cases, the aplication of structural topology optimization should consider the thermal and mechanical requirements. For this reason, a multi-physic and multi-objective approach needs to be developed for the solution of these types of problems. The present work is dedicated to the study of the BESO method (BESO - Bi-directional Evolutionary Structural Optimization) applied to multi-physic systems taking in consideration thermo-mechanical loads as design dependent body loads. The objective functions considered are the compliance and heat capacity of the system. The thermo-mechanical analysis is carried out using a sequential coupling method, where the thermal field response is obtained initially, and in the sequence, the thermal loads or dilation loads are calculated. The bi-objective thermo-mechanical optimization problem is also analysed, where two objective functions are considered simultaneously. To validate the procedures implemented in this work, some 2-D examples of thermo-mechancial systems optimization are presented. The feasibility of the method for the aplication in engineering problems and the comparison of the results obtained using other methods, alows to state that the proposed techniques can be used in the solution of optimization problems of thermo-mechanical systems / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

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In this paper the effects of inertia are explored for the case of a thermal excitation applied on the surface of an infinitely long, solid circular cylinder. The linear uncoupled field equations for a homogeneous, isotropic, thermoelastic medium are used to derive the desired field equations of stress and displacement. The solution procedure included, first, the determination of the thermal boundary value problem from the energy equation which is identically satisfied for the uncoupled condition. Secondly, substitution of the strain-displacement relationships and the previously obtained thermal relation into the equilibrium equation containing inertial effects. The equilibrium equation is the only nonidentically satisfied equation. Thirdly, a solution of this equation is then found in the S-domain by Laplace transformation. Finally, the desired displacement equation is transformed into the time-domain as a function of temperature, time and radius of the cylinder by using inverse Laplace transforms and the calculus of residues.

Further development of the modern aeronautical and aerospace industries will require increased use of composite materials. It is predicted that the influence of composite materials on the aerospace industry will be revolutionary. Composite materials have many good qualities; however, due to the heterogeneity of their thermal and mechanical properties, they are particularly susceptible to the influences of their thermal environment during manufacture and in certain applications. Therefore, it is essential to be able to perform thorough thermoelasticity analyses of these kinds of materials before they can be considered for certain applications where they will be exposed to high temperatures or steep temperature gradients or thermal shock. Up to now, no results for the transient three-dimensional analysis of the thermoelastic response of fiber-reinforced composite materials, which include the mechanical coupling during a thermal shock, have been reported in the open literature; yet there are a number of practical applications where it might be important to know the thermal-mechanical coupling effects. This thesis serves as a first step toward developing a comprehensive model for the transient thermoelastic behavior of fiber-reinforced composite materials which includes full coupling between the thermal and mechanical processes. / M.S.

<p dir="ltr">Stress concentration represents a considerable challenge in 2.5D/ 3D integration systems, primarily due to the inherent structural and material heterogeneities. Discontinuities at interfaces between different materials and at corners lead to the formation of localized stress regions. Furthermore, coefficients of thermal expansion mismatch among materials such as silicon, copper, and polymers exacerbate these stress concentrations, particularly at critical locations including edges, corners, and interfaces. The presence of these localized stresses from both thermal and mechanical loadings heightens the risk of mechanical failure such as crack initiation or crack propagation, thereby underscoring the necessity for meticulous design and analysis to ensure the reliability of these advanced systems.</p><p dir="ltr">Numerical modeling provides insights into the relationship between design, loading, and material behavior leading to failure. Isogeometric analysis (IGA) offers a significant advantage over traditional finite element methods (FEM) by integrating Computer-Aided Design (CAD) and Computer-Aided Engineering (CAE) using NURBS-based approximations. Enriched Isogeometric Analysis (EIGA) enhances this framework by incorporating known behaviors at critical features like crack tips or interfaces to facilitate accurate modeling of flux/stress singularities.</p><p dir="ltr">Asymptotic analysis of flux singularity is systematically studied in order to capture the local thermal behavior around crack tips or junction of multi-material wedges. The general expressions of temperature and flux in polar coordinates are derived. Formulation of EIGA around crack tips or junction of multi-material wedges then presented. A bi-material wedge model is demonstrated to show that singular flux/stress can be obtained in EIGA with a very coarse discretization compared with FEM.</p><p dir="ltr">Configurational force, a key concept in fracture mechanics, describes the energy-driven force that dictates crack propagation and helps predict crack paths and material failure under varying loads and conditions. To develop configurational force for thermoelasticity, configurational optimization problem is introduced. Configurational optimization problem is proposed for determining the optimal location, orientation, and the scaling of a finite-sized heterogeneity inserted into a homogeneous domain. The derivation leads to some important results: a generalized Eshelby energy-momentum tensor, path-independent integral forms for sensitivity, and representation of <i>J-</i>, <i>L-</i> and <i>M-</i>integrals of fracture mechanics. Several illustrative examples of fracture resistant design are solved with EIGA. </p><p dir="ltr">The generalized configurational force for thermoelasticity is derived by solving the configurational optimization problem. Using the general form of Helmholtz free energy potential for thermoelasticity, the generalized configurational force and generalized Eshelby energy-momentum tensor for thermoelasticity are obtained practically without needing the assumption of thermal displacement made in prior literature. </p><p dir="ltr"><br></p><p dir="ltr">Finally, a multiscale modeling for 2.5D/3D integration is demonstrated with all the developed techniques: asymptotic analysis of flux/stress singularities, enriched isogeometric analysis as well as configurational force in thermoelasticity. The one-way coupled multiscale modeling is applied to solve the length scale spanning of package to line. By transferring the global nodal value such as displacement or temperature to the local model as boundary conditions, the one-way coupled is achieved. In local model, a fined-mesh model with EIGA provides more details, and post-processing of configurational force computation leads to a prediction of the direction of crack driving force.</p>