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DOMINGUES, STELLA MARIS PIRES. "ANALYSIS OF BRITTLE ELASTIC MATERIALS THROUGH A CONTINUOUS DAMAGE MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33202@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho lida com uma teoria de dano contínuo, desenvolvida em um contexto termodinâmico, capaz de realizar uma descrição macroscópica da degradação de um material induzida pela deformação em estruturas elásticas frágeis (isto é, falha ocorre sem deformações permanentes). Na modelagem, supõe-se que a energia livre de Helmholtz não depende apenas da deformação e da temperatura absoluta, mas também da variável dano e de seu gradiente. Além disso, para levar em conta os efeitos microscópicos, a potência dos esforços internos não depende apenas da velocidade e de seu gradiente, mas também da taxa de evolução do dano e de seu gradiente. Apesar da sofisticação mecânica da teoria, uma técnica numérica simples, baseada no método dos elementos finitos, é proposta para aproximar a solução dos problemas matemáticos não lineares resultantes. Nestes problemas o acoplamento entre as variáveis dano e deformação é contornado por meio da técnica de partição dos operadores. Para validar o modelo e investigar as características principais do método numérico, diversos exemplos são apresentados para mostrar que os algoritmos utilizados não são sensíveis à malha (mesh dependent).
The present work deals with a continuum damage theory, developed within a thennodynamical framework, able to perform a macroscopic description of material degradation induced by deformation in brittle elastic structures (i.e. failure occurs without permanent deformations). In the modeling, the Helmholtz free energy is supposed to depend not only on the strain and on the absolute temperature but on a damage variable and its gradient as well. Besides, to account for microscopic effects, the power of internal forces depends not only on the velocity and its gradient, but also on the damage velocity and its gradient. Despite the mechanical sophistication of the theory, a simple numerical technique, based on the únite element method, is proposed to approximate the solution of the resulting non linear mathematical problems. The coupling between damage and strain variables in these problems is circumvented by means of a splitting technique. In order to analyse the physical coherence of the model and to access the main features of the numerical method, a number of examples is presented showing that the numerical computations are not mesh dependent.
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CHIMISSO, FULVIO ENRICO GIACOMO. "A CONTINUOUS DAMAGE MODEL FOR MATERIALS WITH ELASTIC-PLASTIC BEHAVIOR." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1994. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33238@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA Mecânica do Dano Contínuo é uma ferramenta promissora para a análise de vida residual em componentes de máquinas e de estruturas. Todavia, não é uma tarefa simples a de se obter uma descrição fisica realística, associada a uma descrição matemática correta, do acoplamento entre a deformação e o amolecimento causado pela degradação da microestrutura. No caso de barras metálicas, a deformação plástica cíclica causa um endurecimento junto com uma degradação na estrutura (dano de fadiga). Por outro lado, a degradação da estrutura induz o amolecimento observado na curva tensão de engenharia vs. deformação. Logo, torna-se importante a modelagem do acoplamento entre plasticidade e dano para que se possa prever de maneira adequada o tempo de vida (ciclos), de um componente estrutural. Muitas tentativas feitas para descrever este tipo de comportamento mostraram-se insatisfatórias. O problema matemático é, em geral, mal posto e uma aproximação numérica da solução é incorreta do ponto de vista fisico. Nestes casos, o fenômeno de localização da deformação é malha-dependente. No presente trabalho, propõe-se uma nova teoria de dano para materiais elasto-plásticos que supera este problema. A teoria tem uma forte base termodinâmica e leva em conta o fenômeno de amolecimento. Uma diferença básica em relação a outros modelos consiste no fato de que a variável escalar D, associada ao dano, é considerada não apenas uma variável de estado mas também uma variável cinemática independente, com abordagem semelhante à apresentada nas teorias de contínuo com microestrutura. As possibilidades de utilização da teoria apresentada são verificadas através da comparação de simulações numéricas com resultados experimentais, para solicitações cíclicas uniaxiais, em barras de almnínioestrutural e em barras de aço austenitico AISI 316 L.
Continuum Damage Mechanics is a promising tool for the failure prediction of structural components. Nevertheless, it is not a simple task to do a mathematically correct and physically realistic description of the strain-softcning behavior due to the degradation of the microstructure. In the case of metallic bars, the cyclic plastic deformation induces a strain-hardening and also a degradation of the structure (fatigue damage). In the other hand, the degradation of the structure induces a softening behavior in the engineering stress-strain curve. Hence, it is very important to model the coupling between plasticity and damage in order to perform an adequate lifetime prevision. Many attempts to describe this type of behavior have been unsatisfatory. The mathematical problem is, in general, ill posed and a numerical approximation of the solution is incorrect from the physical point of view. In this cases the phenomenon of strain localization due to strain-soflzening is mesh dependent. In the present work a new Damage theory for elasto-plastic materials that overcome this problem is proposed. The theory has a strong thermodynarnic basis and take into account the softening behavior. One basic difference from the others models is that the scalar variable D related with damage is taken as an independent kinematic variable, similarly as in the theories of continua with microstructure. The effectiveness and usefulness of the theory is checked by comparing numerical simulations of cyclic uniaxial tests in Aluminiun bars and 316L stainless steel bars with experimental results.
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Chen, Fuh-Sheng. "Damage and failure analysis of continuous fiber-reinforced polymer composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056554068.
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Reese, Sven H. "Adaptive methods for continuous and discontinuous damage modeling in fracturing solids /." Hannover : IBNM, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016312191&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Salleh, Ramli. "Monitoring of damage in continuous fibre reinforced composites by using acoustic emission." Thesis, University of Manchester, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488255.
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Yang, Fangtao. "Simulation of continuous damage and fracture in metal-forming processes with 3D mesh adaptive methodology." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2385/document.
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Ces travaux s'inscrivent dans le cadre des recherches menées dans le cadre d'une collaboration entre le laboratoire Roberval de l'Université de Technologie de Compiègne et l'équipe dans le cadre du projet ANR-14-CE07-0035 LASMIS de l'Institut Charles Delaunay de l'Université de Technologie de Troyes. Nous présentons dans ces travaux une h-méthodologie adaptative tridimensionnelle des éléments finis afin de représenter l'initiation et la propagation des fissures dans des matériaux ductiles. Un modèle élasto-plastique couplé à l'endommagement isotrope proposé par l'équipe du LASMIS/UTT est utilisé. Les applications visées à terme concernent principalement la mise en forme des métaux. Dans ce contexte, une formulation Lagrangienne actualisée est employée et des remaillages fréquents s'avèrent essentiels afin d'une part d'éviter les fortes distorsions d'éléments dues aux grandes déformations plastiques et d'autre part de suivre les modifications de la topologie résultant de la création de fissures. La taille du nouveau maillage doit permettre à moindre coût représenter avec précision l'évolution des gradients des quantités physiques représentatives des phénomènes étudiées (plasticité, endommagement...). Nous proposons des indicateurs empiriques de taille d'éléments basés sur la déformation plastique ainsi que sur l'endommagement. Une courbe définie par morceau représente l'évolution de la taille d'élément suivant la sévérité de la plasticité et le cas échéant de l'endommagement. Les fissures sont représentées par une méthode de destruction d'éléments qui permet une description aisée de la géométrie de ces dernières et une gestion simplifiée de la fissuration sans nul besoin de critères additionnels. En revanche, pour permettre une description réaliste des fissures, ces dernières doivent être représentées par l'érosion des éléments de plus petite taille. Un solveur ABAQUS/Explicit® est utilisé avec des éléments tétraédriques quadratiques (C3D10M) évitant notamment les problèmes de verrouillage numérique survenant lors de l'analyse de structures en matériau compressible ou quasi-incompressible. Le contrôle de la plus petite taille du maillage est important dans un contexte explicite. De surcroît, pour les phénomènes adoucissant, la solution dépend de la taille de maille considérée alors comme un paramètre intrinsèque. Une étude nous a permis de constater que lorsque le maillage est suffisamment raffiné, les effets de la dépendance au maillage se réduisaient. Dans la littérature, les coûts de maillage ou de remaillage fréquents sont souvent considérés comme prohibitifs et de nombreux auteurs s'appuient sur cet argument pour introduire, avec succès certes, des méthodes alternatives qui limitent le coût des opérations de remaillage sans toutefois les éliminer (XFEM par exemple). Nos travaux montrent que le coût d'un remaillage local est négligeable par rapport au calcul. Compte tenu de la complexité de la géométrie et de la nécessité de raffiner le maillage, la seule alternative à ce jour est d'utiliser un mailleur en tétraèdres. La stratégie de remaillage local en tétraèdre s'appuie sur une méthode de bisection suivie si nécessaire d'une optimisation locale du maillage proposé par A. Rassineux en 2003. Le remaillage, même local, doit s'accompagner de procédures de transfert de champ des variables nodales et aux points d'intégration. Les variables nodales sont, comme le fait la plupart des auteurs, transférées en utilisant les fonctions de forme éléments finis. Le transfert de champ en 3D aux points de Gauss et les nombreux problèmes sous-jacents ont été relativement peu abordés dans la littératureThis work is part of the research carried out in the framework of a collaboration between the Roberval laboratory of the Compiègne University of Technology and the team within the framework of the project ANR-14-CE07-0035 LASMIS of the Charles Delaunay Institute of Technology University of Troyes. In this work, we present a three-dimensional adaptive Pi-methodology of finite elements to represent the initiation and propagation of cracks in ductile materials. An elastoplastic model coupled with the isotropic damage proposed by the LASMIS / UTT team is used. The targeted applications will mainly concern the metal forming. In this context, an updated Lagrangian formulation is used and frequent remeshing is essential in order to avoid the strong distortion of elements due to large plastic deformations and to follow the modifications of the topology resulting in the creation of cracks. The size of the new mesh must allow at a lower cost to accurately represent the evolution of the gradients of the physical quantities representative of the studied phenomena (plasticity, damage ...). We propose empirical indicators of size of elements based on the plastic deformation as well as on the damage. A piecewise defined curve represents the evolution of the element size according to the severity of the plasticity and, if appropriate, the damage. The cracks are represented by a method of destruction of elements which allows an easy description of the geometry and a simplified treatment of the cracking without any need for additional criteria. On the other hand, to allow a realistic description of the cracks, the latter must be represented by erosion smaller elements. An ABAQUS / Explicit@ solver is used with quadratic tetrahedral elements (C3DIOM), avoiding in particular the problems of numerical locking occurring during the analysis of structures in compressible or quasi-incompressible material. The control of the smaller mesh size is important in an explicit context. In addition, for softening phenomena, the solution depends on the mesh size considered as an intrinsic parameter. A study has shown that when the mesh is sufficiently refined, the effects of mesh dependence are reduced. In the literature, the costs of frequent meshing or remeshing are often considered prohibitive and many authors rely on this argument to introduce, with success, alternative methods that limit the cost of remeshing operations without eliminating them ( XFEM for example). Our work shows that the cost of local remeshing is negligible compared to the calculation. Given the complexity of the geometry and the need to refine the mesh, the only alternative to date is to use a mesh in tetrahedra. The strategy of local remeshing tetrahedron is based on a bisection method followed if necessary by a local optimization of the grid proposed by A. Rassineux in 2003. The remeshing, even local, must be accompanied by field transfer procedures on both nodal variables and integration points. Node variables are, as most authors do, transferred using finite element shape functions. The 3D field transfer at Gauss points and the many underlying problems have been relatively untouched in the literature. The main difficulties to be solved in order to ensure the "quality" of the transfer concern the limitation of numerical diffusion, the lack of information near borders, the respect of boundary conditions, the equilibrium, the calculation costs, the filtering of the information points, crucial problems in 3D where the number of Gauss points used is several hundred. We propose a so-called "hybrid" method which consists, initially, in extrapolating the data at the Gauss points, in the nodes by diffuse interpolation and then in using the finite element form functions to obtain the value at the point considered
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Thiriot, Kathleen Nichole. "The Effect of Photobiomodulation Therapy on Exercise-Induced Muscle Damage." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6743.
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Purpose: To explore the difference between continuous and pulsed photobiomodulation (PBMT) versus a placebo treatment when using a red-blue light combination over multiple treatment sessions to decrease the symptoms of muscle damage in the quadriceps muscle after a bout of muscle damaging exercise. Methods: Thirty-six healthy, nonactive male and female participants were randomly assigned to one of three groups: continuous PBMT, pulsed PBMT, and placebo treatment. Participants were assessed for muscle damage with knee extension maximal isometric and isokinetic contractions, as well as Visual Analog Scale (VAS) and Lower Extremity Functional Scale (LEFS) scores. Blood creatine kinase (CK) was also analyzed. Participants were given treatment immediately prior to undergoing a bout of damaging eccentric exercise. Participants were treated with PBMT for the next 4 consecutive days for a total of 5 treatments. Results: The continuous treatment group lost significantly less isokinetic average peak torque than the placebo treatment when averaged across all time points postexercise. However, for isometric testing, the continuous group had more reduction in force compared to the placebo group. Between the treatment groups, the continuous treatment group had significantly more muscle soreness measured by the VAS and had significantly less function in daily tasks reported on the LEFS patient-oriented outcome scale. There was no significant difference in level of creatine kinase between the treatment groups. Conclusion: Pulsed photobiomodulation treatments had no significant effect when compared to the placebo group. Continuous photobiomodulation helped to reduce isokinetic force loss, yet exacerbated all other muscle damage markers following exercise relative to the placebo condition.
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DATTA, SAURABH. "ACTIVE FIBER COMPOSITE CONTINUOUS SENSORS FOR STRUCTURAL HEALTH MONITORING." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1061293378.
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Gundmi, Satish Sajjan. "Continuous Time Fatigue Modelling for Non-proportional Loading." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-164950.
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Fatigue analysis is a critical stage in the design of any structural component. Typically fatigue is analysed during post-processing, but as the size of the analysed component increases, the amount of data stored for the analysis increases simultaneously. This increases the computational and memory requirements of the system, intensifying the work load on the engineer. A continuum mechanics approach namely ’Continuous time fatigue model’, for fatigue analysis is available in a prior study which reduces the computational requirements by simultaneously computing fatigue along with the stress. This model implements a moving endurance surface in the stress space along with the damage evolution equation to compute high-cycle fatigue. In this thesis the continuous time fatigue model is compared with conventional model (ie.Cycle counting) to study its feasibility. The thesis also aims to investigate the continuous time fatigue model and an evolved version of the model is developed for non-proportional load cases to identify its limitations and benefits.
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Denaux, Matthieu. "Simulation numérique de la criticité à amorçage de fissure de fretting induit par un chargement vibratoire : Application aux liaisons pale/disque de turbomachine." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI012.
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Le fretting est un endommagement induit par le glissement cyclique à très faible amplitude de deux corps en contact. Il se caractérise par un amorçage d’une fissure en surface, qui peut ensuite propager, menant ainsi à la rupture. Le fretting est présent dans de nombreux secteurs industriels où il constitue un critère de résistance à la fatigue plus ou moins sévère. Ce mémoire s’intéresse aux fissures de fretting qui apparaissent dans une liaison entre pale et disque d’une turbomachine. La sollicitation cyclique de contact est dans ce cas le fruit de la combinaison d’un chargement statique à un chargement vibratoire à très haute fréquence (quelques milliers de Hertz). Pouvoir estimer la durée de vie de la liaison sous un tel chargement est indispensable pour la sécurité des vols. La méconnaissance de certains paramètres d’entrée, la non-proportionnalité du chargement ainsi que les fortes concentrations de contraintes mises en jeu, sont autant de verrous techniques à la modélisation. Ce mémoire de thèse propose une méthode numérique permettant le calcul d’une criticité à amorçage de fretting sous sollicitation vibratoire. Le modèle se décompose en une première phase de calcul des contraintes et déformations cycliques par éléments finis, suivie d’une seconde qui consiste à post-traiter les résultats avec le critère de Dang Van. Le modèle est développé grâce au support d’un banc d’essai innovant qui permet de reproduire les chargements subis par un contact d’une liaison pale/disque. Une utilisation intensive du processus de calcul mis au point permet de tirer des conclusions et de mieux comprendre les phénomènes mis en jeu dans ce type d’endommagement. Une confrontation des différentes études numériques réalisées permet de comparer la représentativité des moyens expérimentaux par rapport aux configurations moteurs réellesFretting is a damage induced by small cyclic slip of two bodies in contact. It is characterized by surface crack initiation, which can then propagate, thus leading to failure. Fretting is present in many industrial environments where it is a more or less severe resistance criterion. This work focuses on the fretting cracks that appear in blade/disk roots of turboshaft engines. In this case, the cyclic contact loading is the result of the combination of a static loading and a high frequency vibratory loading (some thousands of Hertz). Being able to estimate the lifetime of the root under such a solicitation is essential for flight safety. The lack of knowledge of certain input parameters, the non-proportionality of the solicitation as well as the high stress gradient involved, make this phenomenon difficult to predict. This work proposes a numerical method allowing the computation of a fretting crack initiation criterion. First, stresses and deformations fields are computed with finite element method. Then, the post-processing of the fields is done woth Dang Van criterion. The model is developed with the support of an innovative test bench which makes it possible to reproduce the loadings sustained by a a blade/disk root. An intensive use of the computation process developed makes it possible to draw conclusions and provides better understanding of the phenomenon involved in this type of damage. The different numerical studies carried out make it possible to compare the representativeness of the experimental means with respect to the actual engine configurations
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Canino-Vazquez, Iván R. "Aerodynamic Load Characteristics Evaluation and Tri-Axial Performance Testing on Fiber Reinforced Polymer Connections and Metal Fasteners to Promote Hurricane Damage Mitigation." FIU Digital Commons, 2009. http://digitalcommons.fiu.edu/etd/128.
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Damages during extreme wind events highlight the weaknesses of mechanical fasteners at the roof-to-wall connections in residential timber frame buildings. The allowable capacity of the metal fasteners is based on results of unidirectional component testing that do not simulate realistic tri-axial aerodynamic loading effects. The first objective of this research was to simulate hurricane effects and study hurricane-structure interaction at full-scale, facilitating better understanding of the combined impacts of wind, rain, and debris on inter-component connections at spatial and temporal scales. The second objective was to evaluate the performance of a non-intrusive roof-to-wall connection system using fiber reinforced polymer (FRP) materials and compare its load capacity to the capacity of an existing metal fastener under simulated aerodynamic loads. The Wall of Wind (WoW) testing performed using FRP connections on a one-story gable-roof timber structure instrumented with a variety of sensors, was used to create a database on aerodynamic and aero-hydrodynamic loading on roof-to-wall connections tested under several parameters: angles of attack, wind-turbulence content, internal pressure conditions, with and without effects of rain. Based on the aerodynamic loading results obtained from WoW tests, sets of three force components (tri-axial mean loads) were combined into a series of resultant mean forces, which were used to test the FRP and metal connections in the structures laboratory up to failure. A new component testing system and test protocol were developed for testing fasteners under simulated tri-axial loading as opposed to uni-axial loading. The tri-axial and uni-axial test results were compared for hurricane clips. Also, comparison was made between tri-axial load capacity of FRP and metal connections. The research findings demonstrate that the FRP connection is a viable option for use in timber roof-to-wall connection system. Findings also confirm that current testing methods of mechanical fasteners tend to overestimate the actual load capacities of a connector. Additionally, the research also contributes to the development a new testing protocol for fasteners using tri-axial simultaneous loads based on the aerodynamic database obtained from the WoW testing.
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Codes, Rodrigo Nogueira de. "Estudo da MecÃnica da DanificaÃÃo Aplicada ao Concreto com Efeitos de CorrosÃo." Universidade Federal do CearÃ, 2006. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7371.
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A danificaÃÃo e a falha do concreto sÃo largamente investigadas no ramo da MecÃnica do Dano em Meios ContÃnuos. VÃrios modelos existem na literatura e descrevem muito bem uma variedade de fenÃmenos observados, dependendo de sua complexidade. O principal objetivo deste trabalho à investigar e modelar os efeitos da corrosÃo no dano e falha das propriedades do concreto.
Inicialmente, foram feitos ensaios de traÃÃo e de compressÃo em alguns corpos-de- prova intactos sem que tivessem sido submetidos a nenhuma corrosÃo para determinar o comportamento mecÃnico do concreto. Outros foram submetidos a uma cÃmara de corrosÃo acelerada Salt Spray ( durante perÃodos de tempo diferentes) para determinar esse comportamento considerando a corrosÃo. Para o ensaio de traÃÃo, foi desenvolvido um dispositivo composto de peÃas de aÃo, onde se pode realizar esse ensaio de tal maneira a se obter os grÃficos de tensÃo deformaÃÃo utilizando corpos-de-prova cilÃndricos iguais aos usados para a compressÃo. Com esses resultados experimentais, utilizando a MecÃnica do Dano em Meios ContÃnuos, um modelo elÃstico aclopado ao dano à usado para modelar o comportamento do concreto. Em um primeiro estÃgio, a elasticidade isotrÃpica e o dano isotrÃpico ( somente com uma variÃvel escalar D) sÃo usados, mas incluindo-se os efeitos da corrosÃo.
Nos resultados, à analisada a evoluÃÃo do dano no concreto em relaÃÃo ao tempo de exposiÃÃo dos corpos-de-prova na cÃmara de corrosÃo acelerada Salt Spray e em funÃÃo dos carregamentos mecÃnicos.A danificaÃÃo e a falha do concreto sÃo largamente investigadas no ramo da MecÃnica do Dano em Meios ContÃnuos. VÃrios modelos existem na literatura e descrevem muito bem uma variedade de fenÃmenos observados, dependendo de sua complexidade. O principal objetivo deste trabalho à investigar e modelar os efeitos da corrosÃo no dano e falha das propriedades do concreto. Inicialmente, foram feitos ensaios de traÃÃo e de compressÃo em alguns corpos-de- prova intactos sem que tivessem sido submetidos a nenhuma corrosÃo para determinar o comportamento mecÃnico do concreto. Outros foram submetidos a uma cÃmara de corrosÃo acelerada Salt Spray ( durante perÃodos de tempo diferentes) para determinar esse comportamento considerando a corrosÃo. Para o ensaio de traÃÃo, foi desenvolvido um dispositivo composto de peÃas de aÃo, onde se pode realizar esse ensaio de tal maneira a se obter os grÃficos de tensÃo deformaÃÃo utilizando corpos-de-prova cilÃndricos iguais aos usados para a compressÃo. Com esses resultados experimentais, utilizando a MecÃnica do Dano em Meios ContÃnuos, um modelo elÃstico aclopado ao dano à usado para modelar o comportamento do concreto. Em um primeiro estÃgio, a elasticidade isotrÃpica e o dano isotrÃpico ( somente com uma variÃvel escalar D) sÃo usados, mas incluindo-se os efeitos da corrosÃo. Nos resultados, à analisada a evoluÃÃo do dano no concreto em relaÃÃo ao tempo de exposiÃÃo dos corpos-de-prova na cÃmara de corrosÃo acelerada Salt Spray e em funÃÃo dos carregamentos mecÃnicos.
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Потопальська, Ксенія Євгенівна. "Прогнозування надійності елементів конструкцій з локальними корозійними пошкодженнями на основі статистичної оцінки статичної та циклічної міцності." Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/42738.
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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.02.09 – динаміка та міцність машин. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. Дисертаційна робота присвячена розв’язанню актуальної науково-прикладної задачі, яка полягає у розвитку методів комп’ютерного аналізу залишкової міцності та прогнозування надійності елементів конструкцій енергетичного машинобудування, які за час тривалої експлуатації отримали корозійне зношення чи локальні пошкодження. Дослідження здійснені в рамках статистичних методів моделювання, а оцінка характеристик напружено-деформованого стану пошкоджених елементів конструкцій проводилась на основі методу скінчених елементів у тривимірній постановці. Розроблено підхід для теоретичної статистичної оцінки процесів накопичення втоми, який покладено в основу розрахункового методу прогнозу надійності елементів конструкцій, які мають набуті пошкодження корозійної природи на основі статистичної оцінки концентрації напружено-деформованого стану і процесів накопичення втоми. Здійснено комплексні дослідження можливих рівнів концентрації напружень у пошкоджених ділянках конструкцій з урахуванням експлуатаційної варіації навантаження та стохастичного характеру розвитку пошкодження корозійної природи. Виконано практичні розрахункові дослідження надійності елементів конструкцій, які використовуються у транспортуванні енергоносіїв та енергетичному машинобудуванні, що дало можливість розробити рекомендації щодо можливого подовження строку їхньої роботи та можливості відновлення працездатності.Thesis for granting the Degree of Candidate of Technical sciences in specialty 05.02.09 – Dynamics and Strength of Machines. – National Technical University, "Kharkiv Polytechnical Institute", Kharkiv, 2019. The thesis is devoted to the solution of the actual scientific and applied task, which consists in the development of methods of computer analysis of residual durability and the prediction of reliability of elements of power engineering structures, which have been corrosive wear or local damage during long operation. The studies were performed within the framework of statistical modeling methods, and the evaluation of the characteristics of the deformed state of damaged structural elements was performed on the basis of the finite element method (FEM) in three-dimensional formulation. With the use of conceptual approaches for the theoretical assessment of fatigue accumulation processes within the framework of continual damage mechanics, improved methods for assessing the reliability and prediction of the residual life of damaged sections of structural elements, which, unlike known ones, are allowed to taken into account the statistical prediction of possible corrosion sizes. Complex researches of possible levels of stress concentration in the damaged sections of structures are made taking into account the operational variation of load and the stochastic nature of the development of corrosion damage. A statistical analysis and generalization of the obtained results were conducted. The investigation peculiarities of the stress concentration in the damaged areas of structural elements taking into account the operational load variations and the stochastic nature of the corrosion damage. The estimation of its effect on the residual strength is based on the Monte Carlo statistical simulation, taking into account the operational load and the statistical prediction of the possible variation in the size of the corrosion defects. An approach for theoretical statistical estimation of processes of fatigue accumulation is developed, which is the basis of the calculated method of predicting the reliability of structural elements, which will be determined by the simultaneous course of processes of fatigue accumulation and the development of corrosion defect. A set of practical calculation studies aimed at assessing the reliability of structural elements used in energy transportation and power engineering has been carried out and recommendations have been developed on the basis of the conducted research on the possible extension of their life and the possibility of restoration of efficiency. The parameters of damage and the number of cycles to failure of the elbow of the pipeline with a three-dimensional surface defect of mean size were determined taking into account the operational variation of load. The influence of composite bandage on the mean-sized pipeline resource is investigated. Calculations were made to determine the rational dimensions of the composite bandage for the curved portion of the mean-sized defect pipeline. The value of the internal pressure at which the equivalent stresses reach the strength limits in the pipeline with a bandage of different thickness is determined. The residual strength of the pump used in power engineering has been evaluated, taking into account the reduction of the wall thickness of the body parts from erosion-corrosion wear.
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Bandini, Chiara. "FE-numerical modelling of damage in wood using continuum damage mechanics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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In this thesis, the mechanical behavior of a timber joint has been studied. The main task is to model the mechanical behavior of the joint as good as possible. To be able to solve the numerical instabilities of the timber joints, a deeper look needs to be done to the modelling of the wooden material and the steel wood contact. For this thesis a previously developed 3D numerical damage model of wood has been studied. This model has been elaborated by Sandhaas(2012) and it describes crack initiation and propagation of the material based on the concepts of continuum damage mechanics. The basic material model of wood has been implemented as a user material in the UMAT subroutine of ABAQUS. The developed model is giving some numerical instabilities due to the extreme distortion of the elements. During this thesis the model has been enhanced in order to be able to represent the mechanical behavior of wood as good as possible and solve the problem of the model. The modelling outcomes were compared to the results obtained by experimental tests (ref. to Sandaas,2012).The results showed that the first model, a tension test parallel-to grain, had been enhanced. Indeed the results got closer to the experimental value than the original model’s results did. The second model represented a timber joint with slotted-in steel plate with a dowel. The analysis were done with different wood spieces (spruce, beech and azobè). Regarding the spruce, the analysis reached fairly accurate results concerning the capacity load but they were less precise regarding the displacement and the stiffness. The prediction quality was rather poor for the other two species, beech and azobè. It is necessary to find other ways to further enhance the model.Even today a model that is able to represent all three fields (stiffness, capacity load and displacement) accurately doesn’t exist. Good results of one of these lead to bad results of the others. Modelling wood then still represents an evolving challenge.
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Teixeira, Josiele da Silva. "Identificação de danos estruturais via método de Monte Carlo com cadeias de Markov." Universidade do Estado do Rio de Janeiro, 2014. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=6733.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorO presente trabalho apresenta um estudo referente à aplicação da abordagem Bayesiana como técnica de solução do problema inverso de identificação de danos estruturais, onde a integridade da estrutura é continuamente descrita por um parâmetro estrutural denominado parâmetro de coesão. A estrutura escolhida para análise é uma viga simplesmente apoiada do tipo Euler-Bernoulli. A identificação de danos é baseada em alterações na resposta impulsiva da estrutura, provocadas pela presença dos mesmos. O problema direto é resolvido através do Método de Elementos Finitos (MEF), que, por sua vez, é parametrizado pelo parâmetro de coesão da estrutura. O problema de identificação de danos é formulado como um problema inverso, cuja solução, do ponto de vista Bayesiano, é uma distribuição de probabilidade a posteriori para cada parâmetro de coesão da estrutura, obtida utilizando-se a metodologia de amostragem de Monte Carlo com Cadeia de Markov. As incertezas inerentes aos dados medidos serão contempladas na função de verossimilhança. Três estratégias de solução são apresentadas. Na Estratégia 1, os parâmetros de coesão da estrutura são amostrados de funções densidade de probabilidade a posteriori que possuem o mesmo desvio padrão. Na Estratégia 2, após uma análise prévia do processo de identificação de danos, determina-se regiões da viga potencialmente danificadas e os parâmetros de coesão associados à essas regiões são amostrados a partir de funções de densidade de probabilidade a posteriori que possuem desvios diferenciados. Na Estratégia 3, após uma análise prévia do processo de identificação de danos, apenas os parâmetros associados às regiões identificadas como potencialmente danificadas são atualizados. Um conjunto de resultados numéricos é apresentado levando-se em consideração diferentes níveis de ruído para as três estratégias de solução apresentadas.
This work presents a study on the application of Bayesian approach as a technique for solving the inverse problem of structural damage identification, where the integrity of the structure is continuously described by a structural cohesion parameter. The structure chosen for analysis is a simply supported Euler - Bernoulli beam. The damage identification is based on changes in the impulse response of the structure caused by the presence thereof. The direct problem is solved by the finite element method (FEM), which, in turn, is parameterized by the cohesion parameter of the structure. The problem of identifying damages is formulated as an inverse problem, whose solution, from the Bayesian framework, is a posteriori probability distribution of the cohesion parameter, obtained using the sampling methodology of Monte Carlo with Markov Chain. The uncertainties inherent to the measured data will be included in the likelihood function. Three solution strategies are presented. In the Strategy 1, the cohesion parameters of the structure are sampled from probability density functions a posteriori that have the same standard deviation. In the Strategy 2, after a previous analysis of the damage identification process, are determined potentially damaged regions and the cohesion parameters associated with these regions are sampled from probability density functions a posteriori that have different deviations. In the Strategy 3, after a preliminary analysis of the damage identification process, only the parameters associated with regions identifed as potentially damaged are updated. A set of numerical results are presented taking into account different noise levels for the three considered strategies.
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Eskandari, H. (Hamid). "Rate-dependent continuum damage modeling of composite materials." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35696.
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A three-dimensional, phenomenological, tensorial, isotropic, damage model is developed in the framework of continuum damage mechanics for materials whose behavior is governed by elastic deformation coupled with damage. The model was then extended to include isotropic damage for anisotropic materials, as well as rate-dependency behavior caused by damage evolution. The shortcomings of the commonly used scalar variable, as representative of isotropic damage are discussed. It is shown that isotropic damage is best represented by an isotropic tensor of rank four. The damage evolution equations are postulated using strain tensor invariants, based on decomposition of strain energy. The model simulates well the results of static and dynamic uniaxial tension tests on quasiisotropic laminated graphite-epoxy obtained in this study and results, from literature, of uniaxial compression tests on quartzite rock.To determine the material parameters used in the model and to validate the model, a set of material and structural tests, testing a laminate containing a hole, were performed under static and dynamic loading conditions. A tensile version of the Hopkinson bar, suitable for testing of laminated composite materials, is developed to perform dynamic tests. A pulse duration of 200--250 microseconds and peak strain rates of up to 350 s--1 are obtained. Tests performed on a quasi-isotropic lay-up of graphite-epoxy show good repeatability. Comparison of Hopkinson bar tests results with results of tests performed at a quasi-static rate on a hydraulic test machine shows the rate-dependency of this lay-up of graphite-epoxy. Tensile strength and fracture strain are found to be higher for dynamic testing.
The model was evaluated for structural analysis, by implementing the model into a finite element code and analysing a laminate containing a hole. Two techniques are investigated in evaluating the model for structural analysis: stress limiter and mesh limiter. The model is found to be objective with respect to the mesh size. The predicted failure loads using both techniques conform well to the experiments and to the results obtained using one of the existing models.
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Eskandari, Hamid. "Rate-dependent continuum damage modeling of composite materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0024/NQ50155.pdf.
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Yue, Zhenming. "Ductile damage prediction in sheet metal forming processes." Thesis, Troyes, 2014. http://www.theses.fr/2014TROY0025/document.
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L'objectif de ce travail est de proposer un modèle de comportement avec endommagement ductile pour la simulation des procédés de mise en forme de tôles minces qui peut bien représenter le comportement des matériaux sous des trajets de chargement complexes en grandes déformations plastiques. Basé sur la thermodynamique des processus irréversibles, les équations de comportement couplé à l’endommagement tiennent compte des anisotropies initiales et induites, de l’écrouissage isotrope et cinématique et de l’endommagement isotrope ductile. Les effets de fermeture des microfissures, de triaxialité des contraintes et de l’angle de Lode sont introduits pour influencer l’évolution de l’endommagement sous une large gamme de triaxialité des contraintes. La distorsion de la surface de charge est introduite via un tenseur déviateur qui gouverne la distorsion de la surface de charge. A des fins de comparaison, les courbes limites de formage sont tracées basées sur l’approche M-K.Des essais sont conduits sur trois matériaux pour les besoins d’identification et de validation des modèles proposés. L’identification utilise un couplage entre le code ABAQUS et un programme MATLAB via un script en langage Python. Après l’implémentation numérique du modèle dans ABAQUS/Explicite et une étude paramétrique systématique, plusieurs procédés de mise en forme de structures minces sont simulés. Des comparaisons expériences-calculs montrent les performances prédictives de la modélisation proposéeThe objective of this work is to propose a “highly” predictive material model for sheet metal forming simulation which can well represent the sheet material behavior under complex loading paths and large plastic strains. Based on the thermodynamics of irreversible processes framework, the advanced fully coupled constitutive equations are proposed taking into account the initial and induced anisotropies, isotropic and kinematic hardening as well as the isotropic ductile damage. The microcracks closure, the stress triaxiality and the Lode angle effects are introduced to influence the damage rate under a wide range of triaxiality ratios. The distortion of the yield surface is described by replacing the usual stress deviator tensor by a ‘distorted stress’ deviator tensor, which governs the distortion of the yield surfaces. For comparisons, the FLD and FLSD models based on M-K approach are developed.A series of experiments for three materials are conducted for the identification and validation of the proposed models. For the parameters identification of the fully coupled CDM model, an inverse methodology combining MATLAB-based minimization software with ABAQUS FE code through the Python script is used. After the implementation of the model in ABAQUS/Explicit and a systematic parametric study, various sheet metal forming processes have been numerically simulated. At last, through the comparisons between experimental and numerical results including the ductile damage initiation and propagation, the high capability of the fully coupled CDM model is proved
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俞立剛 and Ligang Yu. "Orthotropic damage models for fatigue crack initiation andpropagation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31233995.
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Lacy, Thomas E. Jr. "Distribution effects in damage mechanics." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15937.
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Yu, Ligang. "Orthotropic damage models for fatigue crack initiation and propagation /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13570377.
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Pelà, Luca. "Continuum damage model for nonlinear analysis of masonry structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/30327.
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The present work focuses on the formulation of a Continuum Damage Mechanics model for nonlinear analysis of masonry structural elements. The material is studied at the macro-level, i.e. it is modelled as a homogeneous orthotropic continuum.
The orthotropic behaviour is simulated by means of an original methodology, which is based on nonlinear damage constitutive laws and on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. It is based on establishing a one-to-one mapping relationship between the behaviour of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictitious space and the results are transported to the real field. The application of this idea to strain-based Continuum Damage Models is rather innovative.
The proposed theory is a generalization of classical theories and allows us to use the models and algorithms developed for isotropic materials. A first version of the model makes use of an isotropic scalar damage model. The adoption of such a simple constitutive model in the fictitious space, together with an appropriate definition of the mathematical transformation between the two spaces, provides a damage model for orthotropic materials able to reproduce the overall nonlinear behaviour, including stiffness degradation and strain-hardening/softening response.
The relationship between the two spaces is expressed in terms of a transformation tensor which contains all the information concerning the real orthotropy of the material. A major advantage of this working strategy lies in the possibility of adjusting an arbitrary isotropic criterion to the particular behaviour of the orthotropic material. Moreover, orthotropic elastic and inelastic behaviours can be modelled in such a way that totally different mechanical responses can be predicted along the material axes.
The aforementioned approach is then refined in order to account for different behaviours of masonry in tension and compression. The aim of studying a real material via an equivalent fictitious solid is achieved by means of the appropriate definitions of two transformation tensors related to tensile or compressive states, respectively. These important assumptions permit to consider two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the fictitious space makes use of two scalar variables, which monitor the local damage under tension and compression, respectively. Such a model, which is based on a stress tensor split into tensile and compressive contributions that allows the model to contemplate orthotropic induced damage, permits also to account for masonry unilateral effects. The orthotropic nature of the Tension-Compression Damage Model adopted in the fictitious space is demonstrated. This feature, both with the assumption of two distinct damage criteria for tension and compression, does not permit to term the fictitious space as “isotropic”. Therefore, the proposed formulation turns the original concept of “mapping the real space into an isotropic fictitious one” into the innovative and more general one of “mapping the real space into a favourable (or convenient) fictitious one”. Validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry.
The model is fully formulated for the 2-dimensional case. However, it can be easily extended to the 3-dimensional case. It provides high algorithmic efficiency, a feature of primary importance when analyses of even large scale masonry structures are carried out. To account for this requisite it adopts a strain-driven formalism consistent with standard displacement-based finite element codes. The implementation in finite element programs is straightforward.
Finally, a localized damage model for orthotropic materials is formulated. This is achieved by means of the implementation of a crack tracking algorithm, which forces the crack to develop along a single row of finite elements. Compared with the smeared cracking approach, such an approach shows a better capacity to predict realistic collapsing mechanisms. The resulting damage in the ultimate condition appears localized in individual cracks. Moreover, the results do not suffer from spurious mesh-size or mesh-bias dependence. The numerical tool is finally validated via a finite element analysis of an in-plane loaded masonry shear wall.
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Fason, William Ernest Barnes Robert W. "Static load testing of a damaged, continuous prestressed concrete bridge." Auburn, Ala, 2009. http://hdl.handle.net/10415/1582.
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Liu, Ming. "Multidimensional damage state identification using phase space warping /." View online ; access limited to URI, 2005. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3188065.
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Soyarslan, Celal. "Modelling Damage For Elastoplasticity." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610300/index.pdf.
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A local isotropic damage coupled hyperelastic-plastic framework is formulated in principal axes where thermo-mechanical extensions are also addressed. It is shown that, in a functional setting, treatment of many damage growth models, including ones originated from phenomenological models (with formal thermodynamical derivations), micro-mechanical models or fracture criteria, proposed in the literature, is possible. Quasi-unilateral damage evolutionary forms are given with special emphasis on the feasibility of formulations in principal axes. Local integration procedures are summarized starting from a full set of seven equations which are simplified step by step initially to two and finally to one where different operator split methodologies such as elastic predictor-plastic/damage corrector (simultaneous plastic-damage solution scheme) and elastic predictor-plastic corrector-damage deteriorator (staggered plasticdamage solution scheme) are given. For regularization of the post peak response with softening due to damage and temperature, Perzyna type viscosity is devised. Analytical forms accompanied with algorithmic expressions including the consistent material tangents are derived and the models are implemented as UMAT and UMATHT subroutines for ABAQUS/Standard, VUMAT subroutines for ABAQUS/Explicit and UFINITE subroutines for MSC.Marc. The subroutines are used in certain application problems including numerical modeling of discrete internal cracks, namely chevron cracks, in direct forward extrusion process where comparison with the experimental facts show the predicting capability of the model, isoerror map production for accuracy assessment of the local integration methods, and development two novel necking triggering methods in the context of a damage coupled environment.
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Ngwangwa, Harry Magadhlela. "Assessment of structural damage using operational time responses." Pretoria : [s.n.], 2004. http://upetd.up.ac.za/thesis/available/etd-01312006-141711.
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Priston, Ann-Marie. "Evaluation of stress induced damage in composite material." Thesis, Nottingham Trent University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389766.
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王軍 and Chun Wang. "Development of an anisotropic damage mechanics model in ductile fracture." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31231378.
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Wang, Chun. "Development of an anisotropic damage mechanics model in ductile fracture /." [Hong Kong : University of Hong Kong], 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12362864.
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Williams, Kevin Vaughan. "A physically-based continuum damage mechanics model for numerical prediction of damage growth in laminated composite plates." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0010/NQ39002.pdf.
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Bouffard, Patrice. "Externally prestressing the remaining span of severely damaged continuous concrete beams." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ44899.pdf.
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劉英傑 and Yingjie Liu. "Damage characterization of multi-directional laminates with matrix cracks and delamination." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31235104.
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Liu, Ying-jie. "Damage characterization of multi-directional laminates with matrix cracks and delamination /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B16504434.
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Saha, Reema. "Investigation of a continuum damage model using experimental and numerical techniques." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12542.
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Ho, Kwang-Il. "An anisotropic continuum damage model for creep-dominated, multiaxial loading histories." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/20043.
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Ahci, Elif. "Modeling of viscoelasticity and damage in composite laminates by continuum thermodynamics." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12434.
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Alcazar, Hermann E. "Durability prediction of structural composites through a continuum damage mechanics approach." Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/10868.
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Thesis (Ph. D.)--West Virginia University, 2010.Title from document title page. Document formatted into pages; contains xiv, 176 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 119-125).
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Hayward, Erin M. G. "Atomistic studies on irradiation damage in iron." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34004.
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Two topics involving irradiation damage in alpha-iron have been considered. First, damage cascades representative of those that would be induced by radiation have been simulated using molecular dynamics (MD). The number and type of defects produced are compared for pure iron and iron with a small hydrogen concentration. Second, the inter- action energy between point defects and line dislocations has been calculated for a number of configurations, using both molecular statics methods and calculations based on linear elastic continuum theory and the dipole force tensor. Results from both methods are com- pared. Results from these two topics are relevant for predicting macroscopic behaviors such as creep and plasticity in reactor structural materials.
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Singh, Chandra Veer. "Multiscale modeling of damage in multidirectional composite laminates." Thesis, [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2312.
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李德利 and Deli Li. "Thermodynamic formulation for damaging materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31233764.
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Li, Deli. "Thermodynamic formulation for damaging materials /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1367173X.
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Reberg, Andrew Steven. "An Anisotropic Damage Mechanics Model for Concrete with Applications for Fatigue Loading and Freeze-Thaw Effects." Thesis, North Dakota State University, 2013. https://hdl.handle.net/10365/26994.
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It is well known that the formation and propagation of microcracks within concrete is anisotropic in nature, and has a degrading effect on its mechanical performance. In this thesis an anisotropic damage mechanics model is formulated for concrete which can predict the behavior of the material subjected to monotonic loading, fatigue loading, and freeze-thaw cycles. The constitutive model is formulated using the general framework of the internal variable theory of thermodynamics. Kinetic relations are used to describe the directionality of damage accumulation and the associated softening of mechanical properties. The rate independent model is then extended to cover fatigue loading cycles and freeze-thaw cycles. Two simple softening functions are used to predict the mechanical properties of concrete as the number of cyclic loads as well as freeze-thaw cycles increases. The model is compared with experimental data for fatigue and freeze-thaw performance of plain concrete.DOT-MPC grant
Department of Civil Engineering, North Dakota State University
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Gokulanandam, Prabu. "Homogenization based Continuum Damage Models for Composites under Monotonic and Cyclic Loading." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306951968.
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Zhao, Yuchen. "Multi-scale study of mechanical behaviour of two-phase materials during large deformation and ductile damage." Thesis, Troyes, 2017. http://www.theses.fr/2017TROY0018.
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Cette thèse est dédiée à l’étude du comportement élasto-plastique des matériaux polycristallins multiphasés ainsi que de l’endommagement ductile à différentes échelles. Les hétérogénéités microscopiques ont une influence importante sur la réponse mécanique macroscopique des matériaux. Et l’endommagement ductile est encore difficile à mesurer aux échelles fines. Cette thèse traite des problématiques suivantes : 1. L’évolution du comportement des phases et des grains sous chargements jusqu’à la rupture.2. L’influence de l’hétérogénéité intrinsèque au niveau micro, sur le comportement macroscopique des matériaux biphasés.3. L’influence de la striction et de l’endommagement sur le comportement de familles d’orientation de grains.4. La mesure indirecte de l’endommagement échelle fine par diffraction. Afin d’enquêter sur ces questions, l’acier duplex et le titane biphasé sont testés. La diffraction est utilisée pour effectuer des mesures in situ non-destructive au cours d’essais de traction et jusqu’à la rupture. Des simulations sont réalisées grâce à un modèle auto-cohérent élasto-plastique, dans lequel est introduite la modélisation de l’endommagement ductile. Les données expérimentales aux différentes échelles y sont comparées. En outre, des tests de nano-indentation et observation micrographiques sont effectués pour observer l’évolution spatiale des propriétés mécaniques des phases le long de la striction et jusqu’à la surface de ruptureThe thesis is dedicated to the study of elasto-plastic behavior of multiphase polycrystalline materials and ductile damage at different scales. The microscopic heterogeneities have important influence on the macroscopic mechanical behavior of materials. Ductile damage is still difficult to measure at small scales. The following issues are the main topic involved in this thesis: 1. The evolution of mechanical behavior in phases and groups of grains, under external load until fracture.2. The influence of intrinsic heterogeneity on the macroscopic behavior of two-phase materials.3. The influence of necking and ductile damage, on the behavior of grains with different orientation families.4. The indirect measurement of ductile damage at small scales by diffraction. To answer these questions, duplex steels and two-phase titanium are tested. The diffraction method is used to perform in situ measurements during tensile test until fracture. Predictions are carried out by an elasto-plastic self-consistent model, in which ductile damage have been integrated. Experimental data on different scales are compared with these predictions. In addition, nano-indentation tests are carried out to study the evolution of phases’ mechanical properties along the neck until fracture edge. Microscopic images were also taken in order to observe the fracture surfaces of studied materials
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Hassan, Noha Mohamed. "Damage Development in Static and Dynamic Deformations of Fiber-Reinforced Composite Plates." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/30171.
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A three-dimensional finite element code to analyze coupled thermomechanical deformations of composites has been developed. It incorporates geometric nonlinearities, delamination between adjoining layers, and damage due to fiber breakage, fiber/matrix debonding, and matrix cracking. The three damage modes are modeled using the theory of internal variables and the delamination by postulating a failure envelope in terms of the transverse stresses; the damage degrades elastic moduli. The delamination of adjoining layers is simulated by the nodal release technique. Coupled nonlinear partial differential equations governing deformations of a composite, and the pertinent initial and boundary conditions are first reduced to coupled ordinary differential equations (ODEs) by the Galerkin method. These are integrated with respect to time with the Livermore solver for ODEs. After each time step, the damage in an element is computed, and material properties modified. The code has been used to analyze several static and transient problems; computed results have been found to compare well with the corresponding test results. The effect of various factors such as the fiber orientation, ply stacking sequence, and laminate thickness on composite's resistance to shock loads induced by underwater explosions has been delineated.Ph. D.
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Gyllenskog, James D. "Fatigue Life Analysis of T-38 Aileron Lever Using a Continuum Damage Approach." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/747.
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In a recent investigation conducted by the United States Air Force, the mechanical failure of the aileron lever, manufactured from 2014-T6 aluminum, caused the fatal mishap of a T-38 trainer aircraft. In general the locations of cracks are unknown and must be determined by simulation. In this study we propose to use a continuum damage modeling approach to determine the degradation and damage in a material as the number of cycles of loading increases. This approach successfully predicts the location of crack initiation, propagation path, and propagation rate. A stress-based model in conjunction with the successive initiation technique is utilized.
Successive initiation is based on the idea that damage will accrue in a material. Each element inside a new material will have a value of 0 damage assigned to it. Over time, the damage that occurs due to stresses on individual elements will add until the damage reaches a value of 1. At that point, failure of the element will occur. A code was developed in ANSYS that can draw, mesh, and apply appropriate forces on the aileron lever for successive runs. By using the S-N curve for the 2014-T6 aluminum material, the material damage constants are found. This stress-based damage model is then used to determine the state of damage in each element. Each time the elements are stressed, a particular amount of damage will occur. When an element reaches a specific amount of damage, ANSYS will "kill" the element, resulting in the element no longer adding to the stiffness matrix of the material.
Variability is a common occurrence in all aspects of engineering such as manufacturing, testing, and loading. A Monte Carlo simulation is used to determine the sensitivity of the results to variability of input parameters by ± 15%. Input parameters include loads, material properties and damage model constants. The Monte Carlo simulation indicates the only significant input in the initiation life of the material is the exponential value in the stress-based fatigue life equation. Material properties and load variations in the ± range will not significantly change the life prediction results.
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Tashman, Laith. "Microstructural viscoplastic continuum model for asphalt concrete." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/313.
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This dissertation presents the development of an anisotropic viscoplastic continuum damage model to describe the permanent deformation of asphalt pavements. The model is developed to account for several phenomena that influence the permanent deformation of Asphalt Concrete (AC) at high temperatures. These phenomena include strain rate dependency, confining pressure dependency, dilation, aggregate friction, anisotropy, and damage. The model is based on Perzyna's theory of viscoplasticity with Drucker-Prager yield function modified to account for the microstructure anisotropy and damage. A parametric study was conducted to study the effect of key factors such as inherent anisotropy and damage on the model response. A preliminary investigation was conducted to demonstrate the capabilities of the model and its sensitivity to changes in the microstructure distribution and loading conditions. The model was used to describe laboratory experimental measurements obtained from the Federal Highway Administration (FHWA) Accelerated Loading Facility (ALF). The model had a good match with these experimental measurements. In particular, using the damage parameter, the model was able to capture the point at which AC experienced tertiary creep in a static creep test. A comprehensive experiment was conducted to systematically determine the model parameters and the evolution laws that describe AC hardening, anisotropy, and damage. The experiment consisted of a set of compressive triaxial strength tests conducted at three confining pressures and five strain rates. Based on these experimental measurements, the model was modified to include a nonassociated flow rule. The model was shown to capture the experimental measurements very well. Furthermore, an experiment was conducted to capture and characterize damage evolution in AC due to permanent deformation. AC specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. X-Ray computed tomography and image analysis techniques were used to capture and characterize the evolution of cracks and air voids in the deformed specimens. Damage was found to be a localized phenomenon in the sense that there exists a critical section in an AC specimen that is mainly responsible for failure. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.
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Nofal, Mostafa. "Continuum damage mechanics for plain, fibre-reinforced, and reinforced concrete materials and structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ26860.pdf.
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Hou, Tian. "Fatigue Performance Prediction of North Carolina Mixtures Using Simplified Viscoelastic Continuum Damage Model." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-07102009-011752/.
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Fatigue performance modeling is one the major topics in asphalt concrete modeling work. Currently the only standard fatigue test available for asphalt concrete mixtures is the flexural bending fatigue test, AASHTO T-321. There are several issues associated with flexural fatigue testing, the most important of which are the stress state is not uniform but varies over the depth of the specimen and equipment for fabricating beam specimens is not widely available. Viscoelastic continuum damage (VECD) fatigue testing is a promising alternative to flexural fatigue testing. Different researchers have successfully applied the VECD model to asphalt concrete mixtures using constant crosshead rate direct tension test. However, due to the load level limitation of the new coming Asphalt Mixture Performance Tester (AMPT) testing equipment, there is an immediate need to develop a model that can characterize fatigue performance quickly using cyclic test data. In this study, a simplified viscoelastic continuum damage model developed at NCSU is applied to various North Carolina mixtures, which are used in the NCDOT HWY-2007-7 MEPDG local calibration project. It is shown that the simplified VECD model can predict fatigue tests fairly accurately under various temperature conditions and strain levels. It is also shown that the model can be further utilized to simulate both the strain controlled direct tension fatigue test and the traditional beam fatigue test. In this thesis, simulation results are presented. Conclusions regarding the applicability of the new model are advanced as well as suggestions for further work.
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Josefsson, Axel, and Johan Wedin. "Convergence properties of a continuum damage mechanics model for fatigue of adhesive joints." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-10188.
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The effect of the element length is examined in modelling crack growth in fatigue loading of an adhesive joint. This is done for a cohesive element using an expression for the damage evolution developed at the University of Skövde which is implemented using the UMAT subroutine in the FE-solver Abaqus. These analyses are done for pure mode I loading by analysing a DCB-specimen loaded by a pure moment. An expression is developed in which the critical element length is dependent on the geometry of the specimen (in the form of the wave number of the adhesive joint), the element length, the material properties of the adhesive (in form of the material parameters , , ), the load applied (in form of the stress in the crack tip), the time step used in the analysis and the crack growth rate. It is shown that the results converge by decreasing the element length and the time step used. Therefore an expression for the crack growth rate as a function of the remaining parameters can be determined. Another expression is thereafter developed for the element length needed in order to get a crack growth rate within a certain range of the critical element length. The results show a regular pattern but are not monotone. Therefor two different definitions of the critical element length are tested, either by defining the critical element length as the point where the error is greater than an arbitrary boundary of 1 % of a converged result or where a least square approximation of the error is within 1 % of the converged results. The first method shows a highly irregular result which makes it difficult to develop an expression out of these results. The second method on the other hand gives results that are predictable enough to develop a function out of them. This is done using a regression analysis with all parameters of a third order expression in order to get an expression.