Dissertations / Theses on the topic 'Elasto-plastic materials'
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Li, Wei 1970 May 26. "Yield and geodesic properties of random elasto-plastic materials." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115877.
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Two topics, i.e., the scale effects and the geodesics of random heterogeneous materials will be discussed in this work.When the separation of scales in random media does not hold, the representative volume element (RVE) of deterministic continuum mechanics does not exist in the conventional sense, and new concepts and approaches are needed. This subject is discussed here in the context of microstructures of two types - planar random chessboards, and planar random inclusion-matrix composites -- with microscale behavior being elastic-plastic-hardening (power-law). The microstructure is assumed to be spatially homogeneous and ergodic. Principal issues under consideration are those of yield and incipient plastic flow of statistical volume elements (SVE) on mesoscales, and the scaling trend of SVE to the RVE response on macroscale. Indeed, the SVE responses under uniform displacement (or traction) boundary conditions bound from above (respectively, below) the RVE response, and we show via extensive simulations in plane stress that the larger is the mesoscale, the tighter are both bounds. However, the mesoscale flows under both kinds of loading do not, in general, display normality. Also, with the limitation imposed by currently available computational resources, we do not recover normality (or even a trend towards it) when studying the largest possible SVE domains.
The second topic is the geodesic (i.e., shortest path) character of strain fields occurring in elasto-plastic response of planar inclusion-matrix composites. The composites' spatially random morphology is created by generating the disk centers through a sequential inhibition process based on a poisson point field in plane. Both phases (inclusions and matrix) are elastic-plastic-hardening with the matrix being more compliant and weaker than the inclusions, and perfect bonding everywhere. A quantitative comparison of a response pattern obtained by computational micromechanics with that found only by mathematical morphology indicates that (i) the regions of plastic flow are very close to geodesics, and (ii) a purely geometric, and orders of magnitude more rapid than by computational mechanics assessment of these regions is possible.
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Khdir, Younis Khalid. "Non-linear numerical homogenization : application to elasto-plastic materials." Thesis, Lille 1, 2014. http://www.theses.fr/2014LIL10023/document.
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Ce travail de thèse se veut une contribution à l’homogénéisation numérique des milieux élasto-plastiques hétérogènes aléatoires via des calculs sur des grands volumes. La thèse comporte deux parties principales. La première est dédiée à la réponse élasto-plastique macroscopique des composites, à distribution aléatoire de la seconde phase, sollicités en traction uniaxiale. La deuxième est focalisée sur la réponse macroscopique à la limite d’écoulement des milieux poreux aléatoires sur une large gamme de triaxialités. Dans la première partie, nous décrivons une méthode d’homogénéisation numérique pour estimer la réponse élasto-plastique macroscopique de milieux composites aléatoires à deux phases. La méthode est basée sur des simulations éléments finis utilisant des cellules cubiques tridimensionnelles de différentes tailles mais plus petites que le volume élémentaire représentatif de la microstructure. Dans une seconde partie, nous décrivons une étude d’homogénéisation numérique par éléments finis sur des cellules cubiques tridimensionnelles afin de prédire la surface d’écoulement macroscopique de milieux poreux aléatoires contenant une ou deux populations de vides. La représentativité des résultats est examinée en utilisant des cellules cubiques contenant des vides sphéroïdales, répartis et orientés aléatoirement. Les résultats numériques sont comparés à des critères d’écoulement existants de type GursonThis PhD dissertation deals with the numerical homogenization of heterogeneous elastic-plastic random media via large volume computations. The dissertation is presented in two main parts. The first part is dedicated to the effective elastic-plastic response of random two-phase composites stretched under uniaxial loading. The second part is focused on the effective yield response of random porous media over a wide range of stress triaxialities. In the first part, we describe a computational homogenization methodology to estimate the effective elastic-plastic response of random two-phase composite media. The method is based on finite element simulations using three-dimensional cubic cells of different size but smaller than the deterministic representative volume element of the microstructure. In the second part, we describe using the finite element method a computational homogenization study of three-dimensional cubic cells in order to estimate the effective yield surface of random porous media containing one or two populations of voids. The representativity of the overall yield surface estimates is examined using cubic cells containing randomly distributed and oriented spheroidal voids. The computational results are compared with some existing Gurson-type yield criteria
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Kintzel, Olaf. "Modeling of elasto-plastic material behavior and ductile micropore damage of metallic materials at large deformations /." Bochum : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985340991.
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Lhotellier, Frederic C. "Matrix-fiber stress transfer in composite materials elasto-plastic model with an interphase layer." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/40934.
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The matrix-fiber stress transfer in glass/epoxy composite materials was studied using analytical and experimental methods. The mathematical model that was developed calculates the stress fields in the fiber, interphase, and neighboring matrix near a fiber break. This scheme takes into account the elastic-plastic behavior of both the matrix and the interphase, and it includes the treatment of stress concentration near the discontinuities of the fibers. The radius of the fibers and the mechanical properties of the matrix were varied in order to validate the mathematical model. The computed values for the lengths of debonding, plastic deformation, and elastic deformation in the matrix near the fiber tip were confirmed by measurements taken under polarized light on loaded and unloaded single fiber samples. The fiber-fiber interaction was studied experimentally using dog-bone samples that contained seven fibers forming an hexagonal pattern.
Master of Science
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Kintzel, Olaf [Verfasser]. "Modeling of elasto-plastic material behavior and ductile micropore damage of metallic materials at large deformations / Olaf Kintzel." Aachen : Shaker, 2007. http://d-nb.info/1166511863/34.
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Zangmeister, Tobias [Verfasser], and Ralf [Akademischer Betreuer] Müller. "On the Extended Finite Element Method for the Elasto-Plastic Deformation of Heterogeneous Materials / Tobias Zangmeister. Betreuer: Ralf Müller." Kaiserslautern : Technische Universität Kaiserslautern, 2015. http://d-nb.info/1064868894/34.
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Kintzel, Olaf [Verfasser], Günther [Gutachter] Meschke, Klaus [Gutachter] Hackl, and Mikhail [Gutachter] Itskov. "Modeling of elasto-plastic material behavior and ductile micropore damage of metallic materials at large deformations / Olaf Kintzel ; Gutachter: Günther Meschke, Klaus Hackl, Mikhail Itskov ; Fakultät für Bau- und Umweltingenieurwissenschaften." Bochum : Ruhr-Universität Bochum, 2007. http://d-nb.info/1231542071/34.
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Sotolongo, Wilfredo. "On the numerical implementation of cyclic elasto-plastic material models." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/17594.
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Werner, Todd C. "Elasto-Plastic Impact of a Cantilever Beam Using Non-Linear Finite Elements and Event Simulation." Youngstown State University / OhioLINK, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=ysu997556281.
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Jakel, Roland. "Lineare und nichtlineare Analyse hochdynamischer Einschlagvorgänge mit Creo Simulate und Abaqus/Explicit." Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-171812.
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Der Vortrag beschreibt wie sich mittels der unterschiedlichen Berechnungsverfahren zur Lösung dynamischer Strukturpobleme der Einschlag eines idealisierten Bruchstücks in eine Schutzwand berechnen lässt. Dies wird mittels zweier kommerzieller FEM-Programme beschrieben: a.) Creo Simulate nutzt zur Lösung die Methode der modalen Superposition, d.h., es können nur lineare dynamische Systeme mit rein modaler Dämpfung berechnet werden. Kontakt zwischen zwei Bauteilen lässt sich damit nicht erfassen. Die unbekannte Kraft-Zeit-Funktion des Einschlagvorganges muss also geeignet abgeschätzt und als äußere Last auf die Schutzwand aufgebracht werden. Je dynamischer der Einschlagvorgang, desto eher wird der Gültigkeitsbereich des zugrunde liegenden linearen Modells verlassen. b.) Abaqus/Explicit nutzt ein direktes Zeitintegrationsverfahren zur schrittweisen Lösung der zugrunde liegenden Differentialgleichung, die keine tangentiale Steifigkeitsmatrix benötigt. Damit können sowohl Materialnichtlinearitäten als auch Kontakt geeignet erfasst und damit die Kraft-Zeit-Funktion des Einschlages ermittelt werden. Auch bei extrem hochdynamischen Vorgängen liefert diese Methode ein gutes Ergebnis. Es müssen dafür jedoch weit mehr Werkstoffdaten bekannt sein, um das nichtlineare elasto-plastische Materialverhalten mit Schädigungseffekten korrekt zu beschreiben. Die Schwierigkeiten der Werkstoffdatenbestimmung werden in den Grundlagen erläutertThe presentation describes how to analyze the impact of an idealized fragment into a stell protective panel with different dynamic analysis methods. Two different commercial Finite Element codes are used for this: a.) Creo Simulate: This code uses the method of modal superposition for analyzing the dynamic response of linear dynamic systems. Therefore, only modal damping and no contact can be used. The unknown force-vs.-time curve of the impact event cannot be computed, but must be assumed and applied as external force to the steel protective panel. As more dynamic the impact, as sooner the range of validity of the underlying linear model is left. b.) Abaqus/Explicit: This code uses a direct integration method for an incremental (step by step) solution of the underlying differential equation, which does not need a tangential stiffness matrix. In this way, matieral nonlinearities as well as contact can be obtained as one result of the FEM analysis. Even for extremely high-dynamic impacts, good results can be obtained. But, the nonlinear elasto-plastic material behavior with damage initiation and damage evolution must be characterized with a lot of effort. The principal difficulties of the material characterization are described
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Gu, Tang. "Modélisation multi-échelles du comportement électrique et élasto-plastique de fils composites Cu-Nb nanostructurés et architecturés." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0017/document.
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Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accordNanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (>90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This thesis presents a comprehensive study of the effective electrical and elasto-plastic behavior of this composite material. It is divided into three parts: electrical, elastic and elasto-plastic multiscale modeling. In order to investigate the link between the effective material behavior and the wire microstructure, several homogenization methods are applied which can be separated into two main types: mean-field and full-field theories. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate reliably the effective electrical and elasto-plastic behavior of Cu-Nb wires and save computational time. The electrical models are demonstrated to predict accurately the anisotropic experimental data. Moreover, the mechanical models are also validated by the available ex-situ and in-situ X-ray/neutron diffraction experimental data with a good agreement
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Maddela, Naveen. "Finite Element Analysis of Railway Track Wooden Sleeper." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Railway sleepers have important roles within the complex railroad. Dynamic interaction among Rail, sleeper and ballast supports are vital for the construction of dynamic model track capable of predicting its responses to impact loads due to wheel flats, wheel burns, irregularities of the rail. Railway track deteriorates over time due to the dynamic loading of passing wheeled vehicle. to ensure the secure passing of trains, the track must well design and managed.The objective of this thesis is to determine the stress in wooden rail sleeper by the considering Ballast, Sub ballast, and soil with the help of well-known FEM Tool Ansys Workbench. Material models for wooden sleeper and subgrade are anisotropic elasticity and elasto plastic (Drucker Prager), respectively. To validate FEM results with analytical Zimmermann method, perform the 2D linear static analysis and 3D nonlinear static analysis. The numerical analysis results in Ansys Work bench are presented and discussed the model validation with analytical results. Even though simulation converged it does not mean this model could give results similar to reality. But in my opinion these results are not sufficient to study the behavior of wooden sleeper because limitations in soil mechanics (Soil Models in Ansys Workbench).
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Kato, Motoki, 勉. 宇佐美, Tsutomu Usami, 昭. 葛西, Akira Kasai, and 基規 加藤. "座屈拘束ブレースの繰り返し弾塑性挙動に関する数値解析的研究." 土木学会, 2002. http://hdl.handle.net/2237/8463.
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Silva, Maurício de Carvalho. "Caracterização das propriedades mecânicas e metalúrgicas do aço API 5L X 80 e determinação experimental de curvas J-R para avaliação da tenacidade a fratura." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-11022005-162828/.
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Caracterizar propriedades de resistência à propagação de trinca em materiais dúcteis é um elemento central em métodos de avaliação de integridade estrutural de dutos destinados ao transporte de gás, petróleo e seus derivados que utilizam os aços ARBL. Sendo assim, o objetivo deste trabalho foi estudar as propriedades de fratura dúctil do aço API 5L X80, através da obtenção da curva de resistência à propagação estável de defeitos (curvas J-R) do material. O ensaio de tenacidade à fratura para obtenção da curva J-R foi conduzido utilizando a técnica do corpo-de-prova único (single specimen) empregando o método da flexibilidade no descarregamento (unloading compliance), segundo a norma de ensaios ASTM E1820-96. Os corpos-de-prova compactos C(T) apresentaram espessura B=15mm, largura W=2B e uma relação aproximada entre o tamanho de trinca (a) e a largura, a/W=0,6. O ensaio foi conduzido numa máquina universal de ensaios (MTS) servo-controlada e capacidade máxima de 250kN. Adicionalmente, foram conduzidos ensaios convencionais de tração (limite de escoamento 550MPa, limite de resistência 676MPa e alongamento total em 50mm 27%), ensaios de impacto Charpy (energia absorvida de 220J à 0ºC sentido longitudinal) e análises metalográficas (microestrutura refinada composta por ferrita, colônias de perlita e presença do constituinte MA). Tais caracterizações permitirão uma maior precisão na comparação da curva J-R do aço API 5L X80 em estudo com estudos futuros de tenacidade à fratura.Assessments of crack growth resistance in ductile materials play a key role in structural integrity procedures for high strength, low alloy (HSLA) pipeline steels commonly employed in gas and petroleum trasmission systems. This work presents an investigation of the ductile tearing properties for an API 5L X80 pipeline steel using experimentally measured crack growth resistance curves (J-R curves) for the material. Testing of the X80 pipeline steel employed compact tension (C(T)) fracture specimens to determine the J-R curves based upon the unloading compliance method using a single specimen technique in accordance with the ASTM E1820 standard procedure. The C(T) specimens have thickness B=15mm, width W=2B and a ratio between crack size (a) and width, a/W=0,6. The experimental tests utilized a 250 kN MTS universal machine. Conventional tensile tests were also performed to determine the tensile properties for the tested material: yield strength of 550MPa, tensile strength of 676MPa and elongation of 27% (gage length of 50 mm). The Charpy V-notch impact tests also provided and absorbed energy of 220J at 0ºC. The metallographic analysis showed colonies of perlite and MA constituent islands in a ferrite matrix. This experimental characterization provides additional toughness and mechanical data against which the general behavior of X80 class pipeline steel can be compared.
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Taher, Bilal. "Analyse et modélisation de l'endommagement dû au couplage thermomécanique des multi-matériaux cylindriques." Phd thesis, Université de Technologie de Belfort-Montbeliard, 2012. http://tel.archives-ouvertes.fr/tel-00977567.
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Un grand nombre de systèmes thermomécaniques industriels se trouve confronté à des régimes transitoires plus ou moins rapides suivant la fréquence de fonctionnement. L'amélioration de leurs performances nécessite l'utilisation de nouvelles structures du type multimatériaux ou barrière thermique. En effet, ces matériaux peuvent être de type multicouche en associant plusieurs couches rangées de façon à améliorer le comportement mécanique et thermique d'un système ou alors constitués d'un substrat revêtu d'une succession de couches minces obtenues par projection thermique par exemple.Dans un système donné, ces matériaux subissent généralement des sollicitations cycliques qui peuvent être d'origine thermique et/ou mécanique. Il est donc nécessaire de mieux connaître leur comportement thermomécanique en régimes élastique et plastique. Ainsi, l'étude présentée dans ce travail, limitée ici à des conditions périodiques uniquement d'origine thermique, traite de l'évolution de l'endommagement d'un matériau sous une ou plusieurs formes de fatigue thermique.L'origine de la sollicitation imposée provient d'une condition de flux périodique (sous forme d'échelon, de triangle ou de sinus) prenant en compte les pertes par convection. Sur le plan mécanique, le matériau est supposé fixe sur l'une de ses deux extrémités et libre de se déformer sur l'autre. Les contraintes et les déformations mécaniques dans le matériau proviennent essentiellement des différences des coefficients de dilatation thermique et des gradients de température dans le matériau. La nature variable et transitoire du comportement thermique du matériau permet de suivre l'évolution de la distribution des contraintes et des déformations au sein du matériau.L'étude de son endommagement est menée selon les cas, soit sur des modèles établis directement à partir du comportement thermo élastique soit sur des modèles nécessitant l'étude thermo-élastoplastique. Dans les deux cas, comme la plupart des modèles d'endommagement (Lemaître et Chaboche) rencontrés dans la littérature ne sont valides que sur des matériaux uniformes et homogènes, une recherche de matériau équivalent du multi-matériau étudié était nécessaire. L'équivalence entre le matériau réel et le matériau équivalent repose sur un critère d'équivalence thermique. Les modèles étudiés fournissent dans les deux cas, l'évolution de l'endommagement du matériau, en fonction des paramètres géométriques et aussi de la forme des sollicitations thermiques imposées telles que le coefficient d'échange par convection, l'amplitude et la période du flux imposé.Une application de ces modèles sur un exemple de moteur à combustion interne est proposée à la fin de ce mémoire. Elle montre une prédiction du nombre de cycles (durée de vie) du cylindre moteur en fonction des conditions de fonctionnement utilisées.
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Jakel, Roland. "Grundlagen der Elasto-Plastizität in Creo Simulate - Theorie und Anwendung." Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-87141.
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Der Vortrag beschreibt die Grundlagen der Elasto-Plastizität sowie die softwaretechnische Anwendung mit dem FEM-Programm Creo Simulate bzw. Pro/MECHANICA von PTC. Der erste Teil des Vortrages beschreibt die Charakteristika plastischen Verhaltens, unterschiedliche plastische Materialgesetze, Fließkriterien bei mehrachsiger Beanspruchung und unterschiedliche Verfestigungsmodelle. Im zweiten Vortragsteil werden Möglichkeiten und Grenzen der Berechnung elasto-plastischer Probleme mit der Software dargestellt sowie Anwendungstipps gegeben. Im dritten Vortragsteil schließlich werden verschiedene Beispiele vorgestellt, davon besonders ausführlich das Verhalten einer einachsigen elasto-plastischen Zugprobe vor und nach dem Eintreten der EinschnürdehnungThis presentation describes the basics of elasto-plasticity and its application with the finite element software Creo Simulate (formerly Pro/MECHANICA) from PTC. The first part describes the characteristics of plastic behavior, different plastic material laws, yield criteria for multiaxial stress states and different hardening models. In the second part, the opportunities and limitations of analyzing elasto-plastic problems with the FEM-code are described and user information is provided. The last part finally presents different examples. Deeply treated is the behavior of a uniaxial tensile test specimen before and after elongation with necking appears
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Raghavendra, Rao Arun. "A Unified Constitutive Model For Large Elasto-plastic Deformation." Thesis, 2007. http://hdl.handle.net/2005/570.
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Rapid development and stiff competition in material related industries such as the automotive, demand very high precision in end products in very quick time. The transformation of raw material into an intricate-shaped final product involves various intermediate steps like design, material selection, manufacturing processes, etc. In all these steps, an in-depth understanding of material behavior plays an important role. The available traditional methods such as trial-and-error, especially in the case of die design, become highly inefficient in terms of time and money. This, there is a growing interest in simulation of the final product in order to predict different parameters which are important in design and manufacturing.
Currently available simulation techniques are based on existing theories of plasticity or large deformation. These theories have been developed over several decades and many theoretical and practical issues have been debated over the years. Though the theories have great utility in understanding and solving some practical problems, there are ranges of applications for which no acceptable models are available. Most of these theories are either materials or process-specific with oversimplified real physical situations using assumptions and empirical relations. Development of field equations from first principles to stimulate elasto-plastic deformation is one such, still a subject of on-going discussion.
Materials and composites exhibit hysteresis even at very low stresses, i.e., inelasticity is always present under all types of loading. This observation shows that the representing constitutive relation cannot treat the elastic and plastic deformations separately. The deformation is due to changes in size and shape, and studies with varying strain rates show considerable material sensitivity to the rate of deformation. Therefore, a generalized field equation is developed from first principles in the Eulerian coordinate system using material resistance to changes in size and shape, and their rates. The formulation uses a unified approach representing continuous effect of elastic and plastic strains and strain rates. The field equation involves eight material parameters, viz. bulk modulus, shear modulus, material shear velocity, material bulk viscosity, and four more constants associated with activation points related to deviatoric and volumetric strains and plastic strain rates. The elastic moduli, bulk and shear, are constants, and so also the material viscosities, while plastic stain rates are functions of elastic strain rates. The field equation redces to Cauchy’s equation in the solid limit and Navier-Stokes equation in the fluid limit. Simple experimental measurements are suggested to obtain the numerical values of the material parameters.
Uniaxial tension tests are carried out on commercially available mild steel and aluminium alloy at different strain rates to quantify any variations in the values of material parameters during large deformation. Experimental results and the classical understanding of material deformation reveal the constant nature of elastic moduli during large deformation and, from fluids, the viscosities seem to remain constant. Around the yield region, materials experience a sharp increase in absorbed energy which is modeled to represent the plastic strain rates. The variations and contributions from elastic and plastic strains, both volumetric and deviatoric, and the corresponding stresses are observed. The effects of strain rate on plastic stress and energy absorbed are investigated.
The model is checked for different materials and loading conditions to ascertain the proposed changes to earlier theories. Available experimental data in the literature are used for this purpose. The analysis shows that, though the overall stress-strain relations of different materials look similar, their internal responses differ. The internal response of a material depends on various microstructural factors, like alloying elements, impurities, etc. The present model is able to capture those internal differences between various materials. Numerical solution of different plasticity problems have to be undertaken to ascertain the applicability, generality, realism, accuracy and feasibility of the model.
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"A Generalized Orthotropic Elasto-Plastic Material Model for Impact Analysis." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.40700.
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abstract: Composite materials are now beginning to provide uses hitherto reserved for metals in structural systems such as airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. These structural systems are often subjected to impact loads and there is a pressing need for accurate prediction of deformation, damage and failure. There are numerous material models that have been developed to analyze the dynamic impact response of polymer matrix composites. However, there are key features that are missing in those models that prevent them from providing accurate predictive capabilities. In this dissertation, a general purpose orthotropic elasto-plastic computational constitutive material model has been developed to predict the response of composites subjected to high velocity impacts. The constitutive model is divided into three components – deformation model, damage model and failure model, with failure to be added at a later date. The deformation model generalizes the Tsai-Wu failure criteria and extends it using a strain-hardening-based orthotropic yield function with a non-associative flow rule. A strain equivalent formulation is utilized in the damage model that permits plastic and damage calculations to be uncoupled and capture the nonlinear unloading and local softening of the stress-strain response. A diagonal damage tensor is defined to account for the directionally dependent variation of damage. However, in composites it has been found that loading in one direction can lead to damage in multiple coordinate directions. To account for this phenomena, the terms in the damage matrix are semi-coupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. The overall framework is driven by experimental tabulated temperature and rate-dependent stress-strain data as well as data that characterizes the damage matrix and failure. The developed theory has been implemented in a commercial explicit finite element analysis code, LS-DYNA®, as MAT213. Several verification and validation tests using a commonly available carbon-fiber composite, Toyobo’s T800/F3900, have been carried and the results show that the theory and implementation are efficient, robust and accurate.Dissertation/Thesis
Doctoral Dissertation Civil and Environmental Engineering 2016
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Kintzel, Olaf [Verfasser]. "Modeling of elasto-plastic material behavior and ductile micropore damage of metallic materials at large deformations / from Olaf Kintzel." 2006. http://d-nb.info/985340991/34.
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(13753927), S. Vijay Sundhar. "Endurance limit determination in porous materials." Thesis, 1992. https://figshare.com/articles/thesis/Endurance_limit_determination_in_porous_materials/21047392.
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The theory describing the fatigue mechanism in elasto-plastic material containing pores or inclusions has been developed. An attempt at quantitative determination of the effect of endurance limit reduction by analysis of sizes of plastic zones formed near the inclusions, and their cracking has been -done. The geometrical configuration, consisting of round, horizontal, vertical and angular elliptical inclusions from which a nucleating crack emerged, was considered, and the stress intensity factory of such configurations was analysed. Based on threshold value of 6K below which crack propagation ceases, the critical value of loading stress was determined. Finite element technique was used to obtain theoretical results. A source code developed by Owen and Hinton for solving elastoplastic applications using finite element concept was used for solving the problem. Experimental analysis was done using photoelasticity method. Theoretical results were compared with results from experiments, showing quite good agreement.
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"Micromechanical modeling of dual-phase elasto-plastic materials : influence of the morphological anisotropy, continuity and transformation of the phases." Université catholique de Louvain, 2005. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-02102005-162402/.
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Kuo, Chia-Yuan, and 郭嘉源. "Development of Micro-indentation Test and the inverse computational Method for determination of the flow curve of elasto-plastic Materials." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/76155993612191354782.
Full textAbstract:
碩士國立中正大學
機械系
92
Nowadays, it is a tendency to CAE application for the field of biomedicine. However, how to obtain the material properties and formulate the mathematical model is very important for CAE application in biomedicine problem. At present, the nano-indentation testing is the better method to get the material properties for the nonstandard specimen. However, this method could only measure the superficial properties of material. Therefore, it can’t behave primary properties of the material. So the micro-indentation testing that is used for measuring the Young’s modulus of the biomaterial will be developed in this thesis. The Young’s modulus of the articular cartilage is measured about 6.28MPa by this measurement. Using only the young’s modulus is not sufficient for CAE. Furthermore, the flow curve of elasto-plastic materials cannot be obtain by indentation directly. So the inverse computational method for determination of the flow curve of elasto-plastic Materials will be proposed in this thesis. This inverse method is developed based on the load-depth curve measured by continuous indentation test is set up through the FEM and the ANN. This method for bilinear model and multi-linear model has also been already successful established.
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"Experimental Characterization and Finite Element Modeling of Composites to Support a Generalized Orthotropic Elasto-Plastic Damage Material Model for Impact Analysis." Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.54798.
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abstract: An orthotropic elasto-plastic damage material model (OEPDMM) suitable for impact simulations has been developed through a joint research project funded by the Federal Aviation Administration (FAA) and the National Aeronautics and Space Administration (NASA). Development of the model includes derivation of the theoretical details, implementation of the theory into LS-DYNA®, a commercially available nonlinear transient dynamic finite element code, as material model MAT 213, and verification and validation of the model. The material model is comprised of three major components: deformation, damage, and failure. The deformation sub-model is used to capture both linear and nonlinear deformations through a classical plasticity formulation. The damage sub-model is used to account for the reduction of elastic stiffness of the material as the degree of plastic strain is increased. Finally, the failure sub-model is used to predict the onset of loss of load carrying capacity in the material. OEPDMM is driven completely by tabulated experimental data obtained through physically meaningful material characterization tests, through high fidelity virtual tests, or both. The tabulated data includes stress-strain curves at different temperatures and strain rates to drive the deformation sub-model, damage parameter-total strain curves to drive the damage sub-model, and the failure sub-model can be driven by the data required for different failure theories implemented in the computer code. The work presented herein focuses on the experiments used to obtain the data necessary to drive as well as validate the material model, development and implementation of the damage model, verification of the deformation and damage models through single element (SE) and multi-element (ME) finite element simulations, development and implementation of experimental procedure for modeling delamination, and finally validation of the material model through low speed impact simulations and high speed impact simulations.Dissertation/Thesis
Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019
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Jain, Praveen Kumar. "Towards Measurement And Simulation Of Elasto-Plastic Deformation." Thesis, 2006. http://hdl.handle.net/2005/416.
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The stretch forming process is frequently used in the automotive industry (outer pan-
els, inner panels, stiffeners etc.), the packaging industry and household appliances
sector, to manufacture complicated shapes and curvatures. However it requires accurate prediction of tool geometries and manufacturing parameters to avoid the
currently used trial and error approach. Metal forming is also associated with cer-
tain defects like local thinning, wrinkling, tearing etc. Avoiding such defects and
prediction of spring back presumably requires a thorough understanding of the de-
formation mechanics and material behavior beyond the elastic range.
In the stretch forming operation, material essentially passes through the elastic,
yield point and plastic states. Elastic behavior can be explained based on classical
theory of elasticity wherein linear trend of infinitesimal deformation is expressed by
generalized Hooke’s law. In the plastic range, the theory is based on certain exper-
imental observations of the macroscopic behavior of metals in the uniform state of
combined stresses. Experimentally observed results are idealized into mathematical formulation to describe the complex behavior of metals under combined state of stress. These formulations are based on some assumptions like material behavior is time independent, strain rate effects could be neglected, hysteresis loop and Bauschinger effects which arise from the non-uniformity of the microscopic scale could be disregarded etc. The thermal effects are neglected and material is assumed to be isotropic. Supposedly because of these assumptions existing theory of plastic-
ity does not accurately predict the phenomenon of stretch forming occurring during plastic deformation.
Theories are being developed like that of Rao and Shrinivasa [2002], which consider stresses during deformation as resistance due to shape change, volume change, rate of shape change and rate of volume change. Such theories need variation of material parameters like bulk modulus (K), shear modulus (G), bulk viscosity (µ’)
and shear viscosity (µ) as deformation progreses. Therefore uni-axial tension exper-
iments have been conducted to find out the strains at the corresponding loads. Mild
steel and aluminum have been chosen for the experiments. Chemical and physical
properties of the materials are chosen such that they are very similar to those used
in the automotive industry for stretch forming.
A procedure is developed using uni-axial tension test results to calculate the
material parameters for the entire range of material deformation. For mild steel, bulk modulus and shear modulus decrease and become almost zero as the material deforms from elastic to transition region. After transition zone, both moduli increase and then decrease as material deforms in the strain-hardening region. For aluminum both bulk and shear moduli decrease non-linearly as material deforms from elastic to plastic region. The behavior of bulk modulus and shear modulus are consistent with the stress-strain behavior of the materials. For mild steel as well as aluminum, the bulk and shear viscosities are positive in the elastic region and in the large deformation region the values are small compared to elastic region.
We can separate the various stresses, hydrostatic, deviatoric and viscous stresses,
associated with (µ) and (µ’) and contribution of each to the total stresses can be obtained. It is observed that contribution from the viscous stresses is as high as 5 % when the material is subjected to large strain rate tests.
The strain rate in stretch forming operation may be different from the strain rate at which the material parameters are calculated. Knowing the material para-
meters at one strain rate, the stress-strain curves at different strain rates can be
predicted. The repeatability of computation of the material parameters and contributions from the viscous and non-viscous stresses for large deformation has been ascertained by using different test samples. The material parameters obtained from one set of samples have been applied to different samples and experimental versus predicted stresses have been found to match fairly well.
A lot more work needs to be done to reach the goal of accurately predicting the
behavior during stretch forming. Test data on different materials need to be generated and the new theories need to be validated for compression as well as loading and unloading cases.
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Hu, Hsuan Chi, and 胡軒齊. "A Modified Dao’s Material Analysis Model and Its Application to the Study of Elasto-Plastic Properties of Intermetallic Compound." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/37885566938226641843.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
103
In the solder interconnect technology of flip chip bonding, a thin intermetallic compound layer is likely to form at the interface between solder bump and under bump metallurgy due to the constitutional chemical diffusion. Generally, the shear strength of the intermetallic compound is less than that of the solder. This would influence the drop impact reliability of the solder bump. In addition, as the thickness of intermetallic compound is up to a certain value, a high local stress would commonly occurred at the interface between intermetallic compound layer and its neighborhood, thereby leading to the crack formation and solder bump failure. Thus, it is essential to explore the mechanical property and behavior of intermetallic compound for improving the reliability of the solder bump. Up to date, though the mechanical properties, such as hardness and Young’s modulus, of the intermetallic compound can be measured through the nanoindentation, it is hard to accurately grasp the elasto-plastic behavior of intermetallic compound, i.e., strain hardening exponent and yield stress and, etc., due to the constrains of nano/micro samples fabrication of intermetallic compound and measurement technique. Therefore, the numerical calculation could be the alternative method, which is in replacement of experimental approach, to obtain the mechanical property and behavior of intermetallic compound. Though the Dao model can yield the elasto-plastic behavior, i.e., strain hardening exponent and yielding strength, of the material, whose Young’s modulus is in the range of 10~210 GPa. Nevertheless, the range of the Young’s modulus of the material investigated in the Dao model is extremely extensive. It would result in a lack of the data regarding to development of the Dao model, thereby resulting in a substantially error for Dao model in prediction of elasto-plastic behavior. This thesis constructed the material property and relationship of nanoindentation empiric parameter of the intermetallic compound (Young’s modulus is in the range of 60 ~ 200GPa) by mainly modifying the Dao model to further investigate the elasto-plastic behavior of intermetallic compound. According to the experimental and simulated results, the ratio of initial unloading stiffness and reduced young’s modulus of the intermetallic compound was not constant, and it would vary with different material. This thesis successfully established the relationship between the ratio and nanoindentation empiric parameter. Thus, the strain hardening exponent and yield stress of intermetallic compound were effectively evaluated. Finally, this thesis applied the modified Dao’s material analysis model together with Coffin-Manson fatigue life empiric formula to further investigate the elasto-plastic behavior effect of intermetallic compound on the reliability of SnAg solder bump of the high-density and ultra-fine-pitch 3D chip-on-chip stacking packaging under accelerated thermal cycling loading. The calculated results reveal that the accuracy of prediction of solder bump reliability can be significantly enhanced as the elasto-plastic behavior of the intermetallic compound is taken into account.
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Agarwal, Karn. "Modeling fracture propagation in poorly consolidated sands." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3595.
Full textAbstract:
Frac-pack design is still done on conventional hydraulic fracturing models that employ linear elastic fracture mechanics. However it has become evident that the traditional models of fracture growth are not applicable to soft rocks/unconsolidated formations due to elastoplastic material behavior and strong coupling between flow and stress model. Conventional hydraulic fracture models do not explain the very high net fracturing pressures reported in field and experiments and predict smaller fracture widths than expected. The key observations from past experimental work are that the fracture propagation in poorly consolidated sands is a strong function of fluid rheology and leak off and is accompanied by large inelastic deformation and shear failure leading to higher net fracturing pressures. In this thesis a numerical model is formulated to better understand the mechanisms governing fracture propagation in poorly consolidated sands under different conditions. The key issues to be accounted for are the low shear strength of soft rocks/unconsolidated sands making them susceptible to shear failure and the high permeabilities and subsequently high leakoff in these formations causing substantial pore pressure changes in the near wellbore region. The pore pressure changes cause poroelastic stress changes resulting in a strong fluid/solid coupling. Also, the formation of internal and external filtercakes due to plugging by particles present in the injected fluids can have a major impact on the failure mechanism and observed fracturing pressures.
In the presented model the fracture propagation mechanism is different from the linear elastic fracture mechanics approach. Elastoplastic material behavior and poroelastic stress effects are accounted for. Shear failure takes place at the tip due to fluid invasion and pore pressure increase. Subsequently the tip may fail in tension and the fracture propagates. The model also accounts for reduction in porosity and permeability due to plugging by particles in the injected fluids. The key influence of pore pressure gradients, fluid leakoff and the elastic and strength properties of rock on the failure mechanisms in sands have been demonstrated and found to be consistent with experimental observations.text
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Muthukumar, R. "Effect Of Material Non-Linearity Of Adherends On Fracture Behaviour Of Bimaterial Interface Cracks." Thesis, 2005. http://etd.iisc.ernet.in/handle/2005/1470.
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