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Design and Optimization of Open Truss Interlaced Composite StructuresLiao, Chengqian 18 November 2022 (has links)
This thesis discusses the optimization of non-periodic open structure continuous-fibre PMFRC parts where yarns extend along 3D paths that maximize the specific structural performance of the resulting part for specific load cases. The work focuses on optimizing the geometry of dry yarn structures using steepest ascent (SA) methods and calculating structural performance of the resulting PMFRC parts using finite element analysis (FEA).
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Sur la gestion des bandes de localisations dans les composites stratifiés avec un modèle d'endommagement à taux limité / On the calculation of damage localization in laminated composite structuresLe Mauff, Camille 16 January 2013 (has links)
L'utilisation de limiteurs de localisation est nécessaire pour prendre en compte l'apparition de macro-fissures lors de la simulation de l'évolution des dégradations dans les matériaux composites stratifiés en accord avec des expérimentations. Ceux-ci introduisent un paramètre qui peut être relié à une longueur, ou un temps caractéristique, qui peut alors être identifié. L'approche introduite au LMT-Cachan consiste, dans le cadre dynamique, à utiliser un modèle d'endommagement retardé. Elle est basée sur le fait qu'une fissure ne peut pas apparaître instantanément. Ce modèle donne d'excellents résultats en restant dans le cadre de la dynamique et a l'avantage d'être local en espace. Cependant il requiert une discrétisation temporelle de la taille du temps caractéristique introduit (de l'ordre de la microseconde pour les composites), qui le rend inexploitable pour des simulations de chargement en quasi-statique. Les simulations dans ces cas de chargement nécessitent donc l'utilisation d'un temps caractéristique différent de celui identifié qui ne permet plus de maintenir un résultat en accord avec l'expérience. On cherche alors à adapter les paramètres de la loi d'évolution de l'endommagement afin d'obtenir une propagation de la macro-fissure dans la zone localisée qui soit compatible énergétiquement avec la mécanique de la rupture en contrôlant le taux de restitution d'énergie. Ce travail est dédié à maintenir l'objectivité de la solution et à adapter l'énergie dissipé à la mécanique de la rupture afin de pouvoir utiliser un temps caractéristique exploitable lors de simulations d'éprouvettes en composites sous un chargement quasi-statique. / The use of localization limiters is needed to take into account the apparition of macro-cracks during the simulation of the evolution of degradations in laminated composite materials with respect to experiments. Those introduce a parameter which can be related to a characteristic length, or a characteristic time, and therefore be identified. The approach introduced at LMT-Cachan is, in dynamics, to use a delayed damage model. It's based on the fact that a crack can't appear instantaneously. This model gives excellent results in dynamics and has the advantage to be local in space. Unfortunately, it requires a time discretization related to the characteristic time introduced (of the order of a microsecond for composites), which is far too computationally expensive for quasi-static simulations. Simulations in these loading cases need the use of a different characteristic time from the one identified which can't maintain anymore a result in accordance to experiments. We then adapt the parameters of the damage evolution law to obtain a propagation of a macro-crack in the localized zone that is energetically compatible with fracture mechanics by controlling the strain energy release rate. This work is dedicated to maintain the objectivity of the solution and to adapt the dissipated energy to fracture mechanics to be able to use a characteristic time exploitable for the simulation of composite samples under quasi-static loading.
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Shape Control of Composite Structures with Optimally Placed Piezoelectric PatchesPeriasamy, Ramesh January 2008 (has links)
The problem of shape control of composite laminated smart structures with piezoelectric
patches placed at optimal location is considered in this thesis. Laminated plate structures
with piezoelectric patches for shape control applications are modeled using a shear deformable
plate formulation by including the piezoelectric layers into the plate substrate. A
composite plate finite element model is also developed for composite plates with self-sensing
actuators. Non-linear hysteresis models for piezoelectric materials are presented and discussed.
Numerical simulation of composite plate structures with piezoelectric actuators
is conducted and presented. The optimization problem of finding the optimal location of
actuators using a linear quadratic control algorithm is done and the results are discussed. Static shape control strategies are also discussed.
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Shape Control of Composite Structures with Optimally Placed Piezoelectric PatchesPeriasamy, Ramesh January 2008 (has links)
The problem of shape control of composite laminated smart structures with piezoelectric
patches placed at optimal location is considered in this thesis. Laminated plate structures
with piezoelectric patches for shape control applications are modeled using a shear deformable
plate formulation by including the piezoelectric layers into the plate substrate. A
composite plate finite element model is also developed for composite plates with self-sensing
actuators. Non-linear hysteresis models for piezoelectric materials are presented and discussed.
Numerical simulation of composite plate structures with piezoelectric actuators
is conducted and presented. The optimization problem of finding the optimal location of
actuators using a linear quadratic control algorithm is done and the results are discussed. Static shape control strategies are also discussed.
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Steel Concrete Composite and Hybrid Structures.Lam, Dennis January 2009 (has links)
N/A
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Structural health monitoring systems for impacted isotropic and anisotropic structuresCiampa, Francesco January 2012 (has links)
This thesis investigates the development of ultrasonic Structural Health Monitoring (SHM) systems, based on guided waves propagation, for the localization of low-velocity impacts and the detection of damage mechanisms in isotropic and anisotropic structures. For the identi- cation of the impact point, two main passive techniques were developed, an algorithm-based and an imaging-based method. The former approach is based on the dierences of the stress waves measured by a network of piezoelectric transducers surface bonded on plate-like structures. In particular, four piezoelectric sensors were used to measure the antisymmetrical A0 Lamb mode in isotropic materials, whilst six acoustic emission sensors were employed to record the wave packets in composite laminates. A joint time-frequency analysis based on the magnitude of the Continuous Wavelet Transform was used to determine the time of arrivals of the wave packets. Then, a combination of unconstrained optimization technique associated to a local Newton's iterative method was employed to solve a system of non linear equations, in order to assess the impact location coordinates and the wave group speeds. The main advantages of the proposed algorithms are that they do not require an a-priori estimation of the group velocity and the mechanical properties of the isotropic and anisotropic structures. Moreover, these algorithms proved to be very robust since they were able to converge from almost any guess point and required little computational time. In addition, this research provided a comparison between the theoretical and experimental results, showing that the impact source location and the wave velocity were predicted with reasonable accuracy. The passive imaging-based method was developed to detect in realtime the impact source in reverberant complex composite structures using only one passive sensor. This technique is based on the re- ciprocal time reversal approach, applied to a number of waveforms stored in a database containing the impulse responses of the structure. The proposed method allows achieving the optimal focalization of the acoustic emission source (impact event) as it overcomes the limitations of other ultrasonic impact localization techniques. Compared to a simple time reversal process, the robustness of this approach is experimentally demonstrated on a stiened composite plate. This thesis also extended active ultrasonic guided wave methods to the specic case of dissipative structures showing non-classical nonlinear behaviour. Indeed, an imaging method of the nonlinear signature due to impact damage in a reverberant complex anisotropic medium was developed. A novel technique called phase symmetry analysis, together with frequency modulated excitation signals, was used to characterize the third order nonlinearity of the structure by exploiting its invariant properties with the phase angle of the input waveforms. Then, a \virtual" reciprocal time reversal imaging process was employed to focus the elastic waves on the defect, by taking advantage of multiple linear scattering. Finally, the main characteristics of this technique were experimentally validated.
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Stochastic analysis and robust design of stiffened composite structuresLee, Merrill Cheng Wei, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2009 (has links)
The European Commission 6th Framework Project COCOMAT (Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures by Accurate Simulation of COllapse) was a four and a half year project (2004 to mid-2008) aimed at exploiting the large reserve of strength in composite structures through more accurate prediction of collapse. In the experimental work packages, significant statistical variation in buckling behaviour and ultimate loading were encountered. The variations observed in the experimental results were not predicted in the finite element analyses that were done in the early stages of the project. The work undertaken in this thesis to support the COCOMAT project was initiated when it was recognised that there was a gap in knowledge about the effect of initial defects and variations in the input variables of both the experimental and simulated panels. The work involved the development of stochastic algorithms to relate variations in boundary conditions, material properties and geometries to the variation in buckling modes and loads up to first failure. It was proposed in this thesis that any future design had to focus on the dominant parameters affecting the statistical scatter in the results to achieve lower sensitivity to variation. A methodology was developed for designing stiffened composite panels with improved robustness. Several panels tested in the COCOMAT project were redesigned using this approach to demonstrate its applicability. The original contributions from this thesis are therefore the development of a stochastic methodology to identify the impact of variation in input parameters on the response of stiffened composite panels and the development of Robust Indices to support the design of new panels. The stochastic analysis included the generation of metamodels that allow quantification of the impact that the inputs have on the response using two first order variables, Influence and Sensitivity. These variables are then used to derive the Robust Indices. A significant outcome of this thesis was the recognition in the final report for COCOMAT that the development of a validated robust index should be a focus of any future design of postbuckling stiffened panels.
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Stochastic analysis and robust design of stiffened composite structuresLee, Merrill Cheng Wei, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2009 (has links)
The European Commission 6th Framework Project COCOMAT (Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures by Accurate Simulation of COllapse) was a four and a half year project (2004 to mid-2008) aimed at exploiting the large reserve of strength in composite structures through more accurate prediction of collapse. In the experimental work packages, significant statistical variation in buckling behaviour and ultimate loading were encountered. The variations observed in the experimental results were not predicted in the finite element analyses that were done in the early stages of the project. The work undertaken in this thesis to support the COCOMAT project was initiated when it was recognised that there was a gap in knowledge about the effect of initial defects and variations in the input variables of both the experimental and simulated panels. The work involved the development of stochastic algorithms to relate variations in boundary conditions, material properties and geometries to the variation in buckling modes and loads up to first failure. It was proposed in this thesis that any future design had to focus on the dominant parameters affecting the statistical scatter in the results to achieve lower sensitivity to variation. A methodology was developed for designing stiffened composite panels with improved robustness. Several panels tested in the COCOMAT project were redesigned using this approach to demonstrate its applicability. The original contributions from this thesis are therefore the development of a stochastic methodology to identify the impact of variation in input parameters on the response of stiffened composite panels and the development of Robust Indices to support the design of new panels. The stochastic analysis included the generation of metamodels that allow quantification of the impact that the inputs have on the response using two first order variables, Influence and Sensitivity. These variables are then used to derive the Robust Indices. A significant outcome of this thesis was the recognition in the final report for COCOMAT that the development of a validated robust index should be a focus of any future design of postbuckling stiffened panels.
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Análise teórica e experimental de vigas mistas de aço e concreto e laje com vigotas pré-moldadas e lajotas cerâmicas em um pavimento tipo / Theorical and experimental analysis of composite steel and concrete beams and slabs made by precast elements with lattice and bricks on a frameBruno Eizo Higaki 11 December 2009 (has links)
As vigas mistas de aço e concreto são elementos estruturais que resultam da associação de um perfil de aço laminado, formado a frio ou soldado, e de uma laje de concreto podendo esta ser moldada in loco, pré-fabricada ou com forma de aço incorporada. A construção de vigas mistas com laje de vigotas pré-moldadas de concreto não é prevista pela norma brasileira de dimensionamento de elementos de aço NBR 8800:2008 e poucos estudos foram realizados até o momento. Geralmente, os estudos realizados sobre vigas mistas são feitos em modelos compostos por perfil de aço e uma faixa de laje denominada largura efetiva. Neste trabalho foi desenvolvido um estudo teórico e experimental de vigas mistas fazendo parte de um pavimento tipo. O objetivo principal foi o estudo do comportamento das vigas mistas pertencentes a um pavimento tipo quando submetidas a diferentes tipos de carregamentos, distribuídos e concentrados, verificação da formação de fissuras na laje e a importância de considerar uma faixa de laje maciça na região da largura efetiva sobre as vigas. A análise numérica foi realizada utilizando o pacote comercial ANSYS e por meio das expressões de cálculo fornecidas pela norma brasileira de aço e adaptações para consideração da pré-laje de concreto. Os resultados mostraram um bom desempenho das vigas mistas comparadas com a resistência de cálculo de acordo com as expressões fornecidas pela norma para vigas mistas com pré-laje de concreto e a importância da execução de uma faixa maciça na região da largura efetiva. / The composite steel and concrete beams are structural elements witch results of association by a hot rolled, cold formed or welded steel beam and concrete slab which can be made in site, precast or with steel deck. The design of composite beams made with slab made with precast type lattice joist isn\'t anticipated by the brazilian code and a few studies has been made up to now. Usually, the studies about composite beams are made with steel beam and a concrete\'s zone called a slab\'s effective width. In this work a teorical and experimetal studies were presented with a frame\'s composite beams. The aim of this work was investigate the behaviour when differents loads, distributed and concentrated, were apllied, find out if cracks appeared and the importance of design a solid slab on the effective width\'s regions. The theorical analysis made using the code ANSYS v.10.0 and with expressions of brazilian code for composite beams with precast slabs. The results have shown a good agreement with code\'s analitical models and teh importance of design a solid slab on the effective width\'s regions.
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An Improved Genetic Algorithm for the Optimization of Composite StructuresGantovnik, Vladimir 04 November 2005 (has links)
There are many diverse applications that are mathematically modelled in terms of mixed discrete-continuous variables. The optimization of these models is typically difficult due to their combinatorial nature and potential existence of multiple local minima in the search space. Genetic algorithms (GAs) are powerful tools for solving such problems. GAs do not require gradient or Hessian information. However, to reach an optimal solution with a high degree of confidence, they typically require a large number of analyses during the optimization search. Performance of these methods is even more of an issue for problems that include continuous variables.
The work here enhances the efficiency and accuracy of the GA with memory using multivariate approximations of the objective and constraint functions individually instead of direct approximations of the overall fitness function. The primary motivation for the proposed improvements is the nature of the fitness function in constrained engineering design optimization problems. Since GAs are algorithms for unconstrained optimization, constraints are typically incorporated into the problem formulation by augmenting the objective function of the original problem with penalty terms associated with individual constraint violations. The resulting fitness function is usually highly nonlinear and discontinuous, which makes the multivariate approximation highly inaccurate unless a large number of exact function evaluations are performed. Since the individual response functions in many engineering problems are mostly smooth functions of the continuous variables (although they can be highly nonlinear), high quality approximations to individual functions can be constructed without requiring a large number of function evaluations. The proposed modification improve the efficiency of the memory constructed in terms of the continuous variables. The dissertation presents the algorithmic implementation of the proposed memory scheme and demonstrates the efficiency of the proposed multivariate approximation procedure for the weight optimization of a segmented open cross section composite beam subjected to axial tension load. Results are generated to demonstrate the advantages of the proposed improvements to a standard genetic algorithm. / Ph. D.
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