Thèses : « Structural analysis (Engineering) Composite materials. Finite element method »

1

Geyer, Susanna Elizabeth. « Advanced low order orthotropic finite element formulations ». Diss., Pretoria : [s.n.], 2001. http://upetd.up.ac.za/thesis/available/etd-03062006-114313/.

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Odi, A. R. A. « Bonded Repair of Composite Structures ; A Finite Element Approach ». Thesis, Department of Materials and Medical Sciences, 2009. http://hdl.handle.net/1826/3893.

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This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.

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Odi, A. Randolph A. « Bonded repair of composite structures : a finite element approach ». Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/3893.

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This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.

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Swindeman, Michael James. « A Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials ». University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1324605778.

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Rajagopal, Anurag. « Advancements in rotor blade cross-sectional analysis using the variational-asymptotic method ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51877.

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Rotor (helicopter/wind turbine) blades are typically slender structures that can be modeled as beams. Beam modeling, however, involves a substantial mathematical formulation that ultimately helps save computational costs. A beam theory for rotor blades must account for (i) initial twist and/or curvature, (ii) inclusion of composite materials, (iii) large displacements and rotations; and be capable of offering significant computational savings compared to a non-linear 3D FEA (Finite Element Analysis). The mathematical foundation of the current effort is the Variational Asymptotic Method (VAM), which is used to rigorously reduce the 3D problem into a 1D or beam problem, i.e., perform a cross-sectional analysis, without any ad hoc assumptions regarding the deformation. Since its inception, the VAM based cross-sectional analysis problem has been in a constant state of flux to expand its horizons and increase its potency; and this is precisely the target at which the objectives of this work are aimed. The problems addressed are the stress-strain-displacement recovery for spanwise non-uniform beams, analytical verification studies for the initial curvature effect, higher fidelity stress-strain-displacement recovery, oblique cross-sectional analysis, modeling of thin-walled beams considering the interaction of small parameters and the analysis of plates of variable thickness. The following are the chief conclusions that can be drawn from this work: 1. In accurately determining the stress, strain and displacement of a spanwise non-uniform beam, an analysis which accounts for the tilting of the normal and the subsequent modification of the stress-traction boundary conditions is required. 2. Asymptotic expansion of the metric tensor of the undeformed state and its powers are needed to capture the stiffnesses of curved beams in tune with elasticity theory. Further improvements in the stiffness matrix can be achieved by a partial transformation to the Generalized Timoshenko theory. 3. For the planar deformation of curved laminated strip-beams, closed-form analytical expressions can be generated for the stiffness matrix and recovery; further certain beam stiffnesses can be extracted not only by a direct 3D to 1D dimensional reduction, but a sequential dimensional reduction, the intermediate being a plate theory. 4. Evaluation of the second-order warping allows for a higher fidelity extraction of stress, strain and displacement with negligible additional computational costs. 5. The definition of a cross section has been expanded to include surfaces which need not be perpendicular to the reference line. 6. Analysis of thin-walled rotor blade segments using asymptotic methods should consider a small parameter associated with the wall thickness; further the analysis procedure can be initiated from a laminated shell theory instead of 3D. 7. Structural analysis of plates of variable thickness involves an 8×8 plate stiffness matrix and 3D recovery which explicitly depend on the parameters describing the thickness, in contrast to the simplistic and erroneous approach of replacing the thickness by its variation.

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Chandrashekhara, K. « Geometric and material nonlinear analysis of laminated composite plates and shells ». Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54739.

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An inelastic material model for laminated composite plates and shells is formulated and incorporated into a finite element model that accounts for both geometric nonlinearity and transverse shear stresses. The elasto-plastic material behavior is incorporated using the flow theory of plasticity. In particular, the modified version of Hill's initial yield criterion is used in which anisotropic parameters of plasticity are introduced with isotropic strain hardening. The shear deformation is accounted for using an extension of the Sanders shell theory and the geometric nonlinearity is considered in the sense of the von Karman strains. A doubly curved isoparametric rectangular element is used to model the shell equations. The layered element approach is adopted for the treatment of plastic behavior through the thickness. A wide range of numerical examples is presented for both static and dynamic analysis to demonstrate the validity and efficiency of the present approach. The results for combined nonlinearity are also presented. The results for isotropic results are in good agreement with those available in the literature. The variety of results presented here based on realistic material properties of more commonly used advanced laminated composite plates and shells should serve as references for future investigations.
Ph. D.

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Nezamian, Abolghasem 1968. « Bond strength of concrete plugs embedded in tubular steel piles ». Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/5601.

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Chang, Cherng-Chi. « Finite element analysis of laminated composite free-edge delamination specimens / ». The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612162791.

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Taylor, Joshua Michael. « Nonlinear analysis of steel frames with partially restrained composite connections and full or partially composite girders ». Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19272.

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Widjaja, Budi R. « Analytical investigation of composite diaphragms strength and behavior ». Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07112009-040307/.

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Davis, Dan M. « Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor ». DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/815.

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Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor Dan Davis Experiments measuring the ballistic performance of a commercially available fiberglass armor plate were used to guide the development of constitutive laws for a finite element model of the impact. The test samples are commercially available armor panels, made from E-glass fiber reinforced polyester rated to NIJ level III. Quasi-static tensile tests were used to establish material properties of the test panels. These properties were then used to create models in the explicit finite element code LSDYNA. Ballistic impact testing of the panels was conducted using a compressed gas gun firing spherical steel projectiles oriented normal to the test panel surface. The V50 ballistic limit of these panels was found to be approximately 560 m/s. Tuning parameters in the finite element models were adjusted to match the experimentally measured penetration depths and ballistic limits. Models were created in LSDYNA by adjusting the available material library types 3 and 59 for the target, and material type 15 for the projectile. Type 3 models are isotropic, and resulted in shear punch-out type failures of the plate that poorly replicated the test results. Type 59 takes orthotropic properties into consideration, and can analyze delamination when used with solid elements. Results with model type 59 were significantly better than those using type 3, however, this model was found to vastly underestimate the impact resistance of the plate. With significant adjustments to the material properties in the type 59 model, the LSDYNA simulations were found to better replicate the experimentally observed response of the panels. However, these deformations are questionable since they required quite unrealistic adjustments to the material properties.

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Guven, Deniz. « Development Of A Graphical User Interface For Composite Bridge Finite Element Analysis ». Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12608094/index.pdf.

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Curved bridges with steel/concrete composite girders are used frequently in the recent years. Analysis of these structural systems presents a variety of challenges. Finite element method offers the most elaborate treatment for these systems, however its use is limited in routine design practice due to modeling requirements. In recent years, a finite element program named UTrAp was developed to analyze construction stages of curved/straight composite bridges. The original Graphical User Interface could not be used with the modified computation engine. It is the focus of this thesis work to develop a brand new Graphical User Interface with enhanced visual capabilities compatible with the engine. Pursuant to this goal a Graphical User Interface was developed using C++ programming language together with OPENGL libraries. The interface is linked to the computational engine to enable direct interaction between two programs. In the following thesis work the development of the GUI and the modifications to the computational engine are presented. Moreover, the analysis results pertaining to the newly added features are checked against analytical solutions and recommendations presented in design specifications.

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Chakravarty, Uttam Kumar. « Section builder : a finite element tool for analysis and design of composite ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22640.

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Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Bauchau, Olivier; Committee Member: Craig, James; Committee Member: Hodges, Dewey; Committee Member: Mahfuz, Hassan; Committee Member: Volovoi, Vitali.

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Harursampath, Dineshkumar. « Non-classical non-linear effects in thin-walled composite beams ». Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12501.

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Roy, Samit. « A finite element analysis of adhesively bonded composite joints including geometric nonlinearity, nonlinear viscoelasticity, moisture diffusion and delayed failure ». Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/88624.

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A two-dimensional finite-element computational procedure is developed for the accurate analysis of the strains and stresses in adhesively bonded joints. The large displacements and rotations experienced by the adherends and the adhesive are taken into account by invoking the updated Lagrangian description of motion. The adhesive layer is modeled using Schapery's nonlinear single integral constitutive law for uniaxial and multiaxial states of stress. Effect of temperature and stress level on the viscoelastic response is taken into account by a nonlinear shift factor definition. Penetrant sorption is accounted for by a nonlinear Fickean diffusion model in which the diffusion coefficient is dependent on the penetrant concentration and the dilatational strain. A delayed failure criterion based on the Reiner-Weisenberg failure theory has also been implemented in the finite element code. The applicability of the proposed models is demonstrated by several numerical examples.
Doctor of Philosophy

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Jung, Se-Kwon. « Inelastic Strength Behavior of Horizontally Curved Composite I-Girder Bridge Structural Systems ». Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11618.

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This research investigates the strength behavior of horizontally curved composite I-girder bridge structural systems, and the representation of this behavior by the AASHTO (2004b) LRFD provisions. The primary focus is on the design of a representative curved composite I-girder bridge tested at the FHWA Turner-Fairbank Highway Research Center, interpretation of the results from the testing of this bridge, including correlation with extensive linear and nonlinear finite element analysis solutions, and parametric extension of the test results using finite element models similar to those validated against the physical tests. These studies support the potential liberalization of the AASHTO (2004b) provisions by the use of a plastic moment based resistance, reduced by flange lateral bending effects, for composite I-girders in positive bending.

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Lee, Hsing-Juin. « Determination of the complex modulus of a solid propellant and random vibration analysis of the layered viscoelastic cylinders with finite element method ». Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77816.

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Aeronautical structures, such as aircraft or missiles, are usually highly sophisticated systems often subjected to random vibration environment. Thus, in various design, development, and production stages, laboratory random vibration testing of sampled solid rocket motors on electromagnetic or hydraulic shakers are routinely performed as an important experiment-oriented quality control strategy. Nevertheless, it is crucial to understand the dynamic structural behavior of these layered viscoelastic cylinders such as solid rocket motors under random vibration tests analytically. In this study, a methodology has been developed to deal with the random vibration of a general class of composite structures with frequency-dependent viscoelastic material properties as represented by the example of solid rocket motors. The method combines the finite element method, structural dynamics, strain energy approach, and random vibration analysis concepts. The method is a more powerful technique capable of treating sophisticated random vibration problems with complicated geometry, nonhomogeneous materials, and frequency-dependent stiffness and damping properties. Before the random vibration analysis could proceed, a microcomputer-based dynamic mechanical analyzer system was used together with time-temperature superposition principle to obtain the frequency-dependent dynamic viscoelastic properties of the solid propellant. The strain energy approach has been used to calculate the frequency-dependent equivalent viscoelastic damping which is in turn judiciously represented by a combination of viscous damping and structural damping to accommodate this frequency dependent material property. Modal analysis data together with half power band width calculated at each natural frequency are highly useful guides in the harmonic analysis to achieve computational efficiency. On one hand, the technique used in this study has a hybrid taste in the sense that it makes use of best features and capabilities of both modal analysis and harmonic analysis to achieve the goal of random vibration analysis in addition to the power of finite element technique. The displacement, acceleration and stress power spectra have been obtained for significant points on the rocket model together with their root mean square values. These data can be used for various analyses, testing, design, and other purposes as discussed in later sections of this study.
Ph. D.

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Kim, Joun S. « A Comparison Study of Composite Laminated Plates With Holes Under Tension ». DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1895.

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A Comparison Study of Composite Laminated Plates with Holes under Tension A study was conducted to quantify the accuracy of numerical approximations to deem sufficiency in validating structural composite design, thus minimizing, or even eliminating the need for experimental test. Error values for stress and strain were compared between Finite Element Analysis (FEA) and analytical (Classical Laminated Plate Theory), and FEA and experimental tensile test for two composite plate designs under tension: a cross-ply composite plate design of [(0/90)4]s, and a quasi-isotropic layup design of [02/+45/-45/902]s, each with a single, centered hole of 1/8” diameter, and 1/4" diameter (four sets total). The intent of adding variability to the ply sequences and hole configurations was to gauge the sensitivity and confidence of the FEA results and to study whether introducing enough variability would, indeed, produce greater discrepancies between numerical and experimental results, thus necessitating a physical test. A shell element numerical approximation method through ABAQUS was used for the FEA. Mitsubishi Rayon Carbon Fiber and Composites (formerly Newport Composites) unidirectional pre-preg NCT301-2G150/108 was utilized for manufacturing—which was conducted and tested to conform to ASTM D3039/D3039M standards. A global seed size of 0.020, or a node count on the order of magnitude of 30,000 nodes per substrate, was utilized for its sub-3% error with efficiency in run-time. The average error rate for FEA strain from analytical strain at a point load of 1000lbf was 2%, while the FEA-to-experimental strains averaged an error of 4%; FEA-to-analytical and FEA-to-tensile test stress values at 1000lbf point load both averaged an error value of 6%. Suffice to say, many of these strain values were accurate up to ten-thousandths and hundred-thousandths of an in/in, and the larger stress/strain errors between FEA and test may have been attributed to the natural variables introduced from conducting a tensile test: strain gauge application methods, tolerance stacks from load cells and strain gauge readings. Despite the variables, it was determined that numerical analysis could, indeed, replace experimental testing. It was observed through this thesis that a denser, more intricate mesh design could provide a greater level of accuracy for numerical solutions, which proves the notion that if lower error rates were necessitated, continued research with a more powerful processor should be able to provide the granularity and accuracy in output that would further minimize error rates between FEA and experimental. Additionally, design margins and factors of safety would generally cover the error rates expected from numerical analysis. Future work may involve utilizing different types of pre-preg and further varied hole dimensions to better understand how the FEA correlates with analytical and tensile test results. Other load types, such as bending, may also provide insight into how these materials behave under loading, thus furthering the conversation of whether numerical approximations may one day replace testing all together.

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Grove, Alewyn Petrus. « Development of a finite element based nominal stress extraction procedure for fatigue analysis of welded structures ». Diss., University of Pretoria, 2006. http://upetd.up.ac.za/thesis/available/etd-12182007-125836/.

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Sakarya, Arzu. « Multidisciplinary Design Of An Unmanned Aerial Vehicle Wing ». Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613606/index.pdf.

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In this thesis, the structural design, structural analysis and producibility analysis of an unmanned aerial vehicle wing were performed. Three different wing models, made of different materials, were designed. The wings were aluminum wing model and composite wing models
made of prepreg and wet lay-up. All wings have the same aerodynamic geometry and structural configuration under the same flight conditions. The structural designs of three wings were done by using Unigraphics NX. The finite element modeling of the wings were built by using MSC Patran package program. After the application of the loads on models, structural analyses were performed by MSC Nastran. Finally, the producibility analysis of prepreg wing model was conducted by using FiberSIM package program. The prepreg wing model was selected as optimum design with studies conducted in the study considering weight, producibility, cruise and gust stress and displacement conditions.

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Batista, Fabiano Bianchini. « Identificação de parametros elasticos em placas finas de materiais compositos ». [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265472.

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Orientadores: Eder Lima de Albuquerque, Milton Dias Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-05T00:08:22Z (GMT). No. of bitstreams: 1 Batista_FabianoBianchini_M.pdf: 10144482 bytes, checksum: 8d3245138ba4b557b088eb46adeda69c (MD5) Previous issue date: 2005
Resumo: Neste trabalho são abordados dois métodos para identificar constantes elásticas em materiais compósitos de aplicações estruturais. São métodos que apresentam características não destrutivas, envolvem testes simples e não requerem grandes esforços computacionais. Podem ser aplicados a materiais anisotrópicos e, conseqüentemente,a materiais isotrópicos e ortotrópicos, o que os tomam ferramentas optativas de grande auxílio ao estudo dos materiais compósitos. No primeiro método, as freqüências naturais e os modos próprios adequados, obtidos da análise moda!, serão os dados de entrada para a solução de um sistema linear de equações oriundas da equação diferencial que representa a vibração transversal de placas finas anisotrópicas sob a condição de todos os bordos livres. As constantes elásticas desta equação são os parâmetros desconhecidos e estão associadas aos devidos modos próprios de vibrar. A verificação da precisão deste método é feita baseada em simulações numéricas realizadas em um software de Elementos Finitos, Ansys 7.0, e testado experimentalmente em uma placa isotrópica de aço. O segundo método trata-se de um problema de projeto ótimo cuja solução é feita através da combinação do método dos Elementos Finitos e um método de otimização, ambos executados em um único software comercial, Ansys 7.0. A análise moda! é requerida para obtenção somente das freqüências naturais, que são variáveis utilizadas na função objetivo. A verificação do método é feita em simulações numéricas e testada experimentalmentecom a mesma placa isotrópica de aço utilizada no método anterior. Para esta placa de aço, os resultados obtidos através dos dois métodos foram muitos satisfatórios. Entretanto, com relação à placa anisotrópica utilizada, os resultados obtidos pelo segundo método não foram satisfatórios
Abstract: In this work two methods are analyzed to identify elastic constants in composite materiais of structural application. They are methods that have nondestructive eharacteristie, comprised of simple tests and don't require high computational efforts. They can be employed to anisotropic materials as well as isotropic or ortotropic materials, making them useful alternative tools to composite materiais studies. In the first method, both natural frequencies and suitable mode shapes are input data for the solution of a linear system that come from differential equation that governs the transverse vibration of a free-free thin plate. Elastic constants of this equation are unknown parameters and are associated with vibration mode shape. Numerical simulations of Finite Element software, Ansys 7.0, and experimental modal analysis indicate the accuracy of this method. The second method refers to an optimum design problem and its solution is obtained by combining both Finite Elements and optimization methods in a single eommercial software, Ansys 7.O. The modal analysis is required to obtain only the natural frequencies that are the variables used in the objective function. The second method is verified using numerical simulations and tested experimentally with the same isotropic steel plate used in the first method. Results obtained for this steel plate from both methods were highly satisfactory. In relation to the anisotropic plate, results obtained ftom the second method weren't satisfactory
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

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Heard, William Franklin. « Diagonal and horizontal stiffeners for shear transfer in rigid frame square knees ». Master's thesis, Mississippi State : Mississippi State University, 2006. http://library.msstate.edu/etd/show.asp?etd=etd-11092006-214442.

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Fukasaku, Kotaro. « Explorative study for stochastic failure analysis of a roughened bi-material interface : implementation of the size sensitivity based perturbation method ». Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41114.

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In our age in which the use of electronic devices is expanding all over the world, their reliability and miniaturization have become very crucial. The thesis is based on the study of one of the most frequent failure mechanisms in semiconductor packages, the delamination of interface or the separation of two bonded materials, in order to improve their adhesion and a fortiori the reliability of microelectronic devices. It focuses on the metal (-oxide) / polymer interfaces because they cover 95% of all existing interfaces. Since several years, research activities at mesoscopic scale (1-10µm) have proved that the more roughened the surface of the interface, i.e., presenting sharp asperities, the better the adhesion between these two materials. Because roughness exhibits extremely complex shapes, it is difficult to find a description that can be used for reliability analysis of interfaces. In order to investigate quantitatively the effect of roughness variation on adhesion properties, studies have been carried out involving analytical fracture mechanics; then numerical studies were conducted with Finite Element Analysis. Both were done in a deterministic way by assuming an ideal profile which is repeated periodically. With the development of statistical and stochastic roughness representation on the one hand, and with the emergence of probabilistic fracture mechanics on the other, the present work adds a stochastic framework to the previous studies. In fact, one of the Stochastic Finite Element Methods, the Perturbation method is chosen for implementation, because it can investigate the effect of the geometric variations on the mechanical response such as displacement field. In addition, it can carry out at once what traditional Finite Element Analysis does with numerous simulations which require changing geometric parameters each time. This method is developed analytically, then numerically by implementing a module in a Finite Element package MSc. Marc/Mentat. In order to get acquainted and to validate the implementation, the Perturbation method is applied analytically and numerically to the 3 point bending test on a beam problem, because the input of the Perturbation method in terms of roughness parameters is still being studied. The capabilities and limitations of the implementation are outlined. Finally, recommendations for using the implementation and for furture work on roughness representation are discussed.

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Avachat, Siddharth. « Experimental and numerical analyses of dynamic deformation and failure in marine structures subjected to underwater impulsive loads ». Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44904.

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The need to protect marine structures from the high-intensity impulsive loads created by underwater explosions has stimulated renewed interest in the mechanical response of sandwich structures. The objective of this combined numerical and experimental study is to analyze the dynamic response of composite sandwich structures and develop material-structure-property relations and design criteria for improving the blast-resistance of marine structures. Configurations analyzed include polymer foam core structures with planar geometries. A novel experimental facility to generate high-intensity underwater impulsive loads and carry out in-situ measurements of dynamic deformations in marine structures is developed. Experiments are supported by fully dynamic finite-element simulations which account for the effects of fluid-structure interaction, and the constitutive and damage response of E-glass/polyester composites and PVC foams. Results indicate that the core-density has a significant influence on dynamic deformations and failure modes. Polymeric foams experience considerable rate-effects and exhibit extensive shear cracking and collapse under high-magnitude multi-axial underwater impulsive loads. In structures with identical masses, low-density foam cores consistently outperform high-density foam cores, undergoing lesser deflections and transmitting smaller impulses. Calculations reveal a significant difference between the response of air-backed and water-backed structures. Water-backed structures undergo much greater damage and consequently need to absorb a much larger amount of energy than air-backed structures. The impulses transmitted through water-backed structures have significant implications for structural design. The thickness of the facesheets is varied under the conditions of constant material properties and core dimensions. The results reveal an optimal thickness of the facesheets which maximizes energy absorption in the core and minimizes the overall deflection of the structure.

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Hosseinipour, Milad. « Design and Development of an Intra-Ventricular Assistive Device For End Stage Congestive Heart Failure Patients : Conceptual Design ». University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1372726495.

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Khadke, Kunal R. « Material design using surrogate optimization algorithm ». Thesis, 2015. http://hdl.handle.net/1805/6694.

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Indiana University-Purdue University Indianapolis (IUPUI)
Nanocomposite ceramics have been widely studied in order to tailor desired properties at high temperatures. Methodologies for development of material design are still under effect. While finite element modeling (FEM) provides significant insight on material behavior, few design researchers have addressed the design paradox that accompanies this rapid design space expansion. A surrogate optimization model management framework has been proposed to make this design process tractable. In the surrogate optimization material design tool, the analysis cost is reduced by performing simulations on the surrogate model instead of high fidelity finite element model. The methodology is incorporated to and the optimal number of silicon carbide (SiC) particles, in a silicon-nitride(Si3N4) composite with maximum fracture energy [2]. Along with a deterministic optimization algorithm, model uncertainties have also been considered with the use of robust design optimization (RDO) method ensuring a design of minimum sensitivity to changes in the parameters. These methodologies applied to nanocomposites design have a significant impact on cost and design cycle time reduced.

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Narasimhan, S. « Three Dimensional Viscoplastic And Geomertrically Non-Linear Finite Element Analysis Of Adhesively Bonded Joints ». Thesis, 1998. http://etd.iisc.ernet.in/handle/2005/2166.

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(6532391), Nicolas Guarin-Zapata. « Modeling and Analysis of Wave and Damaging Phenomena in Biological and Bioinspired Materials ». Thesis, 2021.

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There is a current interest in exploring novel microstructural architectures that take advantage of the response of independent phases. Current guidelines in materials design are not just based on changing the properties of the different phases but also on modifying its base architecture. Hence, the mechanical behavior of composite materials can be adjusted by designing microstructures that alternate stiff and flexible constituents, combined with well-designed architectures. One source of inspiration to achieve these designs is Nature, where biologically mineralized composites can be taken as an example for the design of next-generation structural materials due to their low density, high-strength, and toughness currently unmatched by engineering technologies.

The present work focuses on the modeling of biologically inspired composites, where the source of inspiration is the dactyl club of the Stomatopod. Particularly, we built computational models for different regions of the dactyl club, namely: periodic and impact regions. Thus, this research aimed to analyze the effect of microstructure present in the impact and periodic regions in the impact resistance associated with the materials present in the appendage of stomatopods. The main contributions of this work are twofold. First, we built a model that helped to study wave propagation in the periodic region. This helped to identify possible bandgaps and their influence on the wave propagation through the material. Later on, we extended what we learned from this material to study the bandgap tuning in bioinspired composites. Second, we helped to unveil new microstructural features in the impact region of the dactyl club. Specifically, the sinusoidally helicoidal composite and bicontinuous particulate layer. For these, structural features we developed finite element models to understand their mechanical behavior.

The results in this work help to elucidate some new microstructures and present some guidelines in the design of architectured materials. By combining the current synthesis and advanced manufacturing methods with design elements from these biological structures we can realize potential blueprints for a new generation of advanced materials with a broad range of applications. Some of the possible applications include impact- and vibration-resistant coatings for buildings, body armors, aircraft, and automobiles, as well as in abrasion- and impact-resistant wind turbines.

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Thèses sur le sujet « Structural analysis (Engineering) Composite materials. Finite element method »

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