Dissertations / Theses: 'Large deformation large strain'

1

Brown, Rebecca A. (Rebecca Ann) 1976. "Large strain deformation of PETG as processing temperatures." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88847.

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Rückert, Jens, and Arnd Meyer. "Kirchhoff Plates and Large Deformation." Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-96896.

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In the simulation of deformations of plates it is well known that we have to use a special treatment of the thickness dependence. Therewith we achieve a reduction of dimension from 3D to 2D. For linear elasticity and small deformations several techniques are well established to handle the reduction of dimension and achieve acceptable numerical results. In the case of large deformations of plates with non-linear material behaviour there exist different problems. For example the analytical integration over the thickness of the plate is not possible due to the non-linearities arising from the material law and the large deformations themselves. There are several possibilities to introduce a hypothesis for the treatment of the plate thickness from the strong Kirchhoff assumption on one hand up to some hierarchical approaches on the other hand.

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Honeker, Christian. "Large strain deformation behavior of oriented triblock copolymer cylinders." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10430.

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Parsons, Ethan M. (Ethan Moore) 1972. "Mechanics of large-strain deformation of particle-modified polymers." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37048.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (p. 267-274).
Over the past several decades, engineering polymers have become increasingly prevalent in the manufacture of virtually all types of products. Polymers are substantially less dense than metals, easy to machine, and readily formed into quite complex geometries. The properties of polymers may be altered by the introduction of second-phase particles. Typically, soft, rubber particles are added to increase fracture toughness while rigid, mineral particles are added to reduce costs or to increase stiffness, thermostability, or porosity. The deformation to large strains of particle-modified thermoplastic polymers is investigated. Blends with rubber particles and blends with calcium carbonate particles are considered. A novel experimental technique is utilized to characterize the three-dimensional deformation of polycarbonate blends and high-density polyethylene blends during uniaxial tension tests. True stress, true strain, volumetric strain, and full-field contours of strain are extracted from images of the deforming specimens. The experimental results are used to construct and verify single-particle and multi-particle micromechanical models.
(cont.) In the micromechanical models, the stress triaxiality ratio and the properties of the particles, matrix, and interfaces are varied in order to determine their effects on local and macroscopic deformation. A constitutive model for polymers with perfectly bonded or debonding rigid particles is developed based on the knowledge gained from the experiments and micromechanical models.
by Ethan Moore Parsons.
Ph.D.

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Hillmansen, Stuart. "Large strain bulk deformation and brittle tough transitions in polythene." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272493.

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Paloumbi, Vassia Vasiliki. "Monitoring large strain deformation in the processing of polyethylene pipes." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497537.

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Barnhoorn, Auke. "Rheological and microstructural evolution of carbonate rocks during large strain torsion experiments /." [Zurich] : [s.n.], 2003. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15309.

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Hoover, Luke Daniel. "Large Strain Plastic Deformation of Traditionally Processed and Additively Manufactured Aerospace Metals." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570139729633.

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Ssemakula, Hamzah. "Manufacturihng of heavy rings and large copper canisters by plastic deformation." Doctoral thesis, KTH, Production Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3682.

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Plastic deformation processes transform material fromas-received state to products meeting certain requirements inproperties, microstructure and shape. To achieve thistransformation, the relationship between material response andprocess conditions should be understood. This is usuallycomplicated by the complex conditions describing the actualprocess. Numerous techniques including empirical, physical,analytical and numerical can be employed.

In this thesis, numerical technique supported by lab- andfull-scale experiments has been employed to analyse the formingparameters. The first part of the thesis is focused on the useof such parameters to predict occurrence of material poresduring manufacturing of bearing rings. The second part dealswith the influence of forming parameters on the grain sizeduring fabrication of large copper canisters for encapsulationof nuclear waste. The primary task has been to study with thehelp of commercial FE-codes the magnitude and distribution offorming parameters such as accumulated effective strain,temperature, instantaneous hydrostatic pressure and materialflow at different stages of the forming process. In the firstpart, two types of ring manufacturing routes, which result inpore free and pore loaded rings are studied and compared.Material elements located in different areas of the workpiecehave been traced throughout the process. Results of theaccumulated strain and instant hydrostatic pressure have beenanalysed and presented in pressure-strain space. Itsassumed that high hydrostatic pressures together with higheffective strains are favourable for pore closure. Area of theworkpiece with unfavourable parameters have been identified andcompared with ultrasonic test results. Good agreement has beenobtained. Based on the results of this analysis, a new conceptfor avoiding pores in manufacturing of yet heavier rings hasbeen presented. The concept proposes a lighter upsetting in theinitial stage of the process and a more efficient piercingwhich results in higher hydrostatic pressure and bigger andbetter distributed effective strain.

In the second part of the thesis, the influence of formingparameters such as effective strain and temperature on thefinal grain size of the product has been studied in laboratoryscale. As-cast billets of cylindrical shape were extruded atdifferent temperatures and reductions. It has been shown thatthe grain size in the final product should be small in order toenable ultrasonic tests and to guarantee resistance towardscreep and corrosion. Simulations for different materialelements located at different distances from the axis ofsymmetry of the initial cylindrical workpiece have been carriedout. In this way, the parameters describing the deformationhistory of the elements have been determined as functions oftime. Experimentally obtained pre- and post deformation grainsize in the corresponding locations of the material weredetermined. Its concluded that low temperature coupledwith high effective strain are conducive for obtaining a smallgrain size. Based on the beneficial conditions for extrusion ofcopper, a more detailed FE-analysis of a full-scale industrialprocess is carried out. A coarse-grained cast ingot of purecopper is heated and by upset forging formed into a cylinder,which is then punched into a hollow blank for subsequentextrusion. The blank is extruded over a mandrel through a45-degree semi-angle die. Accumulated effective strain andtemperatureas functions of the tubular wall thickness havebeen studied at five different locations along the tubularaxis. Forming load requirement as function of tool displacementfor each stage of the process has been determined. Strain andtemperature levels obtained have been related to the grain sizeinterval obtained in the earlier work. It has been concludedthat the levels reached are within the interval that ensures asmall grain size. A similar analysis has been carried out forforging of large copper lids and bottoms. Die designmodifications to improve the grain size in the lid and tooptimise the forging process with respect to forging load andmaterial yield have been proposed. A method requiring a smallforging load for fabrication of the lids has been analysed

Keywords:Pores; grain size; low forging load; effective strain;temperature; hydrostatic pressure; extrusion; forging;canister; lid; rings

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Yao, Shulong. "Highly Stretchable Miniature Strain Sensor for Large Dynamic Strain Measurement." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849674/.

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This thesis aims to develop a new type of highly stretchable strain sensor to measure large deformation of a specimen subjected to dynamic loading. The sensor was based on the piezo-resistive response of carbon nanotube(CNT)/polydimethysiloxane (PDMS) composites thin films, some nickel particles were added into the sensor composite to improve the sensor performance. The piezo-resistive response of CNT composite gives high frequency response in strain measurement, while the ultra-soft PDMS matrix provides high flexibility and ductility for large strain measuring large strain (up to 26%) with an excellent linearity and a fast frequency response under quasi-static test, the delay time for high strain rate test is just 30 μs. This stretchable strain sensor is also able to exhibit much higher sensitivities, with a gauge factor of as high as 80, than conventional foil strain gauges.

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Rückert, Jens. "Kirchhoff Plates and Large Deformations - Modelling and C^1-continuous Discretization." Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-121275.

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In this thesis a theory for large deformation of plates is presented. Herein aspects of the common 3D-theory for large deformation with the Kirchhoff hypothesis for reducing the dimension from 3D to 2D is combined. Even though the Kirchhoff assumption was developed for small strain and linear material laws, the deformation of thin plates made of isotropic non-linear material was investigated in a numerical experiment. Finally a heavily deformed shell without any change in thickness arises. This way of modeling leads to a two-dimensional strain tensor essentially depending on the first two fundamental forms of the deformed mid surface. Minimizing the resulting deformation energy one ends up with a nonlinear equation system defining the unknown displacement vector U. The aim of this thesis was to apply the incremental Newton technique with a conformal, C^1-continuous finite element discretization. For this the computation of the second derivative of the energy functional is the key difficulty and the most time consuming part of the algorithm. The practicability and fast convergence are demonstrated by different numerical experiments.

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Regmi, Gaurav. "EFFECTS OF ADDITION OF LARGE PERCENTAGES OF FLY ASH ON LIQUEFACTION BEHAVIOR OF SAND." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1461.

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The liquefaction resistance of a saturated medium sand with varying amount of non-plastic type F fly ash was evaluated by conducting cyclic triaxial tests. The test results were used to evaluate the effect of addition of various percentages of fly ash on the liquefaction resistance of Ottawa sand. The effect of cyclic shear stress and confining pressure on liquefaction resistance of the sand-fly ash mixtures was the main scope of this research. In addition, the Young's Modulus and Damping Ratio for sand-fly ash mixtures were also determined. A comprehensive experimental program was conducted in which 50 stress controlled cyclic triaxial tests were performed on a clean sand, sand containing 25%, 30%, 50% and 70% fly ash at a constant relative density of 50%. The results show that sand containing 25% fly ash has the highest liquefaction resistance under cyclic loading in comparison to clean sand and sand containing 30%, 50% and 70% fly ash. The cyclic resistance goes on decreasing as the fly ash content further increases. The test result also shows that the liquefaction resistance of the clean sand and sand containing 70% fly ii ash is almost same. The test results were also examined in terms of the conceptual framework of Thevanayagam (2000). The effects on liquefaction resistance were also measured in terms of pore water pressure generation and deformation of the sample. As the confining pressure increases, shear stress required to cause initial liquefaction of the sample also increases. Modulus of Elasticity was seen to increase with increase in confining pressure and decrease with increase in axial strain for all cases of sand-fly ash mixtures used in these tests. The damping ratio of the sample increases with the increase in axial strain upto about 1% and then it either decreases or remains constant thereafter. There was no clear correlation of damping ratio with confining pressure.

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Al-Quraishi, Ali Abdul Hussain. "The Deformation and Fracture Energy of Natural Rubber Under High Strain Rates." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1185471043.

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Bondsman, Benjamin. "Numerical modeling and experimental investigation of large deformation under static and dynamic loading." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104227.

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Small kinematics assumption in classical engineering has been in the center of consideration in structural analysis for decennaries. In the recent years the interest for sustainable and optimized structures, lightweight structures and new materials has grown rapidly as a consequence of desire to archive economical sustainability. These issues involve non-linear constitutive response of materials and can only be accessed on the basis of geometrically and materially non-linear analysis. Numerical simulations have become a conventional tool in modern engineering and have proven accuracy in computation and are on the verge of superseding time consuming and costly experiments.\newlineConsequently, this work presents a numerical computational framework for modeling of geometrically non-linear large deformation of isotropic and orthotropic materials under static and dynamic loading. The numerical model is applied on isotropic steel in plane strain and orthotropic wood in 3D under static and dynamic loading. In plane strain Total Lagrangian, Updated Lagrangian, Newmark-$\beta$ and Energy Conserving Algorithm time-integration methods are compared and evaluated. In 3D, a Total Lagrangian static approach and a Total Lagrangian based dynamic approach with Newmark-$\beta$ time-integration method is proposed to numerically predict deformation of wood under static and dynamic loading. The numerical model's accuracy is validated through an experiment where a knot-free pine wood board under large deformation is studied. The results indicate accuracy and capability of the numerical model in predicting static and dynamic behaviour of wood under large deformation. Contrastingly, classical engineering solution proves its inaccuracy and incapability of predicting kinematics of the wood board under studied conditions.
Små kinematikantaganden inom klassisk ingenjörsteknik har varit centralt för konstruktionslösningar under decennier. Under de senaste åren har intresset för hållbara och optimerade strukturer, lättviktskonstruktioner och nya material ökat kraftigt till följd av önskan att uppnå ekonomisk hållbarhet. Dessa nya konstruktionslösningar involverar icke-linjär konstitutiv respons hos material och kan endast studeras baserad på geometriskt och materiellt olinjär analys. Numeriska simuleringar har blivit ett konventionellt verktyg inom modern ingenjörsteknik och visat sig ge noggrannhet i beräkning och kan på sikt ersätta tidskrävande och kostsamma experiment.\newlineDetta examensarbete presenterar ett numeriskt beräkningsramverk för modellering av geometrisk olinjäritet med stora deformationer hos isotropa och ortotropa material vid statisk och dynamisk belastning. Den numeriska modellen appliceras på isotropiskt stål i plantöjning och ortotropisk trä i 3D vid statisk och dynamisk belastning. I fallet med plantöjning jämförs och utvärderas den Totala Lagrangianen, Uppdaterade Lagrangianen, Newmark-$\beta$ och Energi Konserverings Algoritm metoderna. I 3D föreslås en statisk Total Lagrangian metod och en dynamisk Total Lagrangian-baserad metod med Newmark-$\beta$ tidsintegreringsmetod för att numeriskt förutse statisk och dynamisk deformation hos trä. Den numeriska modellens noggrannhet valideras genom ett experiment där en kvistfri furuplanka studeras under stora deformationer. Resultaten bekräftar noggrannhet och förmåga hos den numeriska modellen att förutse statiska och dynamiska processer hos trä vid stora deformationer. Däremot, visar klassisk ingenjörslösning brist på förmåga att förutse trä plankans kinematik under studerade förhållanden.

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Wu, Xianping Kalidindi Surya Doherty R. D. "Prediction of crystallographic texture evolution and anisotropic stress-strain response during large plastic deformation in alpha-titanium alloys /." Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1122.

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Giardina, Ronald J. Jr. "On The Ramberg-Osgood Stress-Strain Model And Large Deformations of Cantilever Beams." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2377.

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In this thesis the Ramberg-Osgood nonlinear model for describing the behavior of many diﬀerent materials is investigated. A brief overview of the model as it is currently used in the literature is undertaken and several misunderstandings and possible pitfalls in its application is pointed out, especially as it pertains to more recent approaches to ﬁnding solutions involving the model. There is an investigation of the displacement of a cantilever beam under a combined loading consisting of a distributed load across the entire length of the beam and a point load at its end and new solutions to this problem are provided with a mixture of numerical techniques, which suggest strong mathematical consistency within the model for all theoretical assumptions made. A physical experiment was undertaken and the results prove to be inaccurate when using parameters derived from tensile tests, but when back calculating parameters from the beam test the model has a 14.40% error at its extreme against the experimental data suggesting the necessity for further testing.

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上田, 恭平. "砂の力学モデルとしての多重せん断モデルの大変形解析の定式化およびその適用性に関する研究." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120801.

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Beese, Allison M. "Experimental investigation and constitutive modeling of the large deformation behavior of anisotropic steel sheets undergoing strain-induced phase transformation." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67576.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 139-146).
The strain-induced phase transformation from austenite to martensite is responsible for the high strength and ductility of TRansformation-Induced Plasticity (TRIP)- assisted steels. The large deformation behavior of conventional steels is governed by crystallographic slip. In the case of TRIP steels, the phase transformation provides an additional microstructural deformation mechanism, which has a particularly strong effect on the strain hardening response at the macroscopic level. This thesis work develops a new plasticity model for TRIP steels that accounts for the effect of phase transformation. In particular, the large deformation behavior of 1.5mm thick stainless steel 301LN sheets at room temperature is studied in detail. Several techniques for quantifying the martensite volume fraction are evaluated including micrography, X-ray diffraction, neutron diffraction, magnetic saturation, and magnetic permeability measurements. The latter is then used to measure the evolution of the martensite content throughout mechanical experiments. The experimental program for different stress states includes experiments for uniaxial tension, uniaxial compression, equi-biaxial tension, pure shear, and transverse plane strain tension. The resulting experimental data demonstrate the influence of both the stress triaxiality and Lode angle parameter on the austenite-to-martensite transformation kinetics. A stress-state dependent transformation kinetics evolution equation is proposed which describes the martensite content as a function of plastic strain, the stress triaxiality, and the Lode angle parameter. Furthermore, a phenomenological plasticity model is developed comprising an anisotropic yield function, an isotropic hardening law, and a nonlinear kinematic hardening law with initial back stress. The isotropic hardening law expresses the increase in deformation resistances as a function of the plastic strain and the martensite content and is directly coupled with the stress-state dependent transformation kinetics equation. As a result, the model is able to describe the experimentally observed effect of stress state on the macroscopic hardening response. The constitutive model is implemented into a finite element program and used to simulate all experiments performed. The model predictions agree well with the experimental results for a wide range of stress states and for both specimens with homogeneous and heterogeneous stress and strain fields.
by Allison M. Beese.
Ph.D.

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Balg, Martina, and Arnd Meyer. "Fast simulation of (nearly) incompressible nonlinear elastic material at large strain via adaptive mixed FEM." Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-96915.

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The main focus of this work lies in the simulation of the deformation of mechanical components which consist of nonlinear elastic, incompressible material and that are subject to large deformations. Starting from a nonlinear formulation one can derive a discrete problem by using linearisation techniques and an adaptive mixed finite element method. This turns out to be a saddle point problem that can be solved via a Bramble-Pasciak conjugate gradient method. With some modifications the simulation can be improved.

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Schmidt, Hansjörg [Verfasser], Arnd [Akademischer Betreuer] Meyer, Lutz [Gutachter] Tobiska, and Thomas [Gutachter] Apel. "Anisotropic Viscoelasticity at Large Strain Deformations / Hansjörg Schmidt ; Gutachter: Lutz Tobiska, Thomas Apel ; Betreuer: Arnd Meyer." Chemnitz : Technische Universität Chemnitz, 2018. http://d-nb.info/1214821030/34.

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21

Hapsari, Gemala. "Identification of inelastic cyclic behaviour of thin metal sheets under very large strain from instrumented micro forming process." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD010.

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Le succès de l'industrialisation des micro-produits dépend des processus de conception et de fabrication. Une étape cruciale est la caractérisation du matériau utilisé dans les simulations numériques. Bien qu’il confère certaines propriétés mécaniques au matériau, l’essai de traction est loin de représenter la déformation complète subie par le matériau. Par conséquent, un autre test, Micro Incremental Deformation (Micro InDef), test présentant une déformation non homogène et riche en information, est développé sur la base du micro formage incrémental mono-point (µSPIF).Pour modéliser la formabilité du matériau (en particulier l'endommagement de matériaux), le modèle de Lemaitre est choisi en raison de sa capacité à modéliser le comportement du matériau en s'appuyant sur la mécanique des milieux continus et la thermodynamique de processus irréversibles. Dans cette étude, le Micro InDef test en tant que test de caractérisation de matériau est validé. De plus, en utilisant une méthode d’identifiabilité, il est prouvé que les paramètres matériaux identifiés sont des paramètres physiques, et non un simple lissage mathématique. Une fois le modèle de Lemaitre identifié, des tests expérimentaux et des simulations éléments finis sont effectués sur des tests de traction, des tests de cisaillement, des courbes limites de formage et des essais hors plan, afin de vérifier la fiabilité et l'adaptabilité de notre identification.Cette étude est finalement appliquée à un projet industriel dans le domaine des connecteurs, qui utilise principalement les alliages de cuivre comme matériau constitutifs
The success of micro product's industrialization depends on the conception, design and manufacturing process. A crucial step is the characterization of the material used in the numerical simulations. Although it gives some mechanical properties of material, tensile test is far from representing the complete deformation produced in the material. Therefore another test, Micro Incremental Deformation (Micro InDef), test which has non homogeneous deformation and which is rich in charactérization data is developped, based on Micro Single Point Incremental Forming (µSPIF).To modelise the limit of formability (especially the damage of materials), Lemaitre's constitutive model is chosen due to its possibility to define the material behaviour by using continuum mechanics and thermodynamics of irreversible processes. Within this study, Micro InDef as material characterization test is validated. Moreover, the material parameters identified are proven to be physical parameters, instead of only mathematical fitting, using an identifiability method. Once Lemaitre's model is identified, experimental tests and finite element simulations are performed on tensile tests, shearing tests, forming limit tests and out-of-plane tests, to verify the reliability and adaptability of our identification.This study is applied in an industrial project within the connector domain, which use copper alloys

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Kajberg, Jörgen. "Displacement field measurement using digital speckle photography for characterisation of materials subjected to large deformations and high strain rates /." Luleå, 2003. http://epubl.luth.se/1402-1544/2003/35.

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Ren, Honghao. "Experimental and numerical analysis of orthotropic deformations of wood using Finite Strain Theory (large deformations) and the Finite Element Method (FEM) in 2D." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104778.

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This thesis involves the derivation of a constitutive model under large deformationtheory using Updated Lagrange method applied on an orthotropic material.Thefollowing aspects are included in this thesis work: introduction, theory, FEM implementation, derivation of constitutive model, calibration, result, discussion, conclusion and the future work. This thesis studies the deformation behavior of wood, which is widely used as aconstruction material, in an advanced and more detailed way by analyzing the mechanical properties of wood from both, the application in laboratory and theoreticalcalculation under large deformation theory. A non-linear elastic constitutive model is proposed, derived and calibrated using asimple inverse analysis procedure. The calibration process was performed to identify8 constitutive parameters A1 − A8 of the constitutive model by performing inverseanalysis against relevant experimental data acquired using the Aramis system. Theresults in the comparison were extracted from the specimen when it is both intangential orientation and radial orientation. The project work will be dedicated to the development of a Finite Element Method(FEM) code implemented in MATLAB scripts which was directly used to study themechanical properties of the orthotropic wood material when hyper-elastic behavioris assumed. The results will contain three parts: 1) study of the influence of pith location onthe load required to deform the specimen specimen, 2) reaction force comparisonof the model results against experimental results, and, 3) comparison of the GreenLagrangian strain pattern over the specimen between the experimental data and themodel’s results.

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Wang, Ruoya. "Novel theoretical and experimental frameworks for multiscale quantification of arterial mechanics." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47718.

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The mechanical behavior of the arterial wall is determined by the composition and structure of its internal constituents as well as the applied traction-forces, such as pressure and axial stretch. The purpose of this work is to develop new theoretical frameworks and experimental methodologies to further the understanding of arterial mechanics and role of the various intrinsic and extrinsic mechanically motivating factors. Specifically, residual deformation, matrix organization, and perivascular support are investigated in the context of their effects on the overall and local mechanical behavior of the artery. We propose new kinematic frameworks to determine the displacement field due to residual deformations previously unknown, which include longitudinal and shearing residual deformations. This allows for improved predictions of the local, intramural stresses of the artery. We found distinct microstructural differences between the femoral and carotid arteries from non-human primates. These arteries are functionally and mechanically different, but are geometrically and compositionally similar, thereby suggesting differences in their microstructural alignments, particularly of their collagen fibers. Finally, we quantified the mechanical constraint of perivascular support on the coronary artery by mechanically testing the artery in-situ before and after surgical exposure.

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Li, Tianyu. "On the Formulation of a Hybrid Discontinuous Galerkin Finite Element Method (DG-FEM) for Multi-layered Shell Structures." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/82962.

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A high-order hybrid discontinuous Galerkin finite element method (DG-FEM) is developed for multi-layered curved panels having large deformation and finite strain. The kinematics of the multi-layered shells is presented at first. The Jacobian matrix and its determinant are also calculated. The weak form of the DG-FEM is next presented. In this case, the discontinuous basis functions can be employed for the displacement basis functions. The implementation details of the nonlinear FEM are next presented. Then, the Consistent Orthogonal Basis Function Space is developed. Given the boundary conditions and structure configurations, there will be a unique basis function space, such that the mass matrix is an accurate diagonal matrix. Moreover, the Consistent Orthogonal Basis Functions are very similar to mode shape functions. Based on the DG-FEM, three dedicated finite elements are developed for the multi-layered pipes, curved stiffeners and multi-layered stiffened hydrofoils. The kinematics of these three structures are presented. The smooth configuration is also obtained, which is very important for the buckling analysis with large deformation and finite strain. Finally, five problems are solved, including sandwich plates, 2-D multi-layered pipes, 3-D multi-layered pipes, stiffened plates and stiffened multi-layered hydrofoils. Material and geometric nonlinearities are both considered. The results are verified by other papers' results or ANSYS.
Master of Science

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Crabbé, Blandine. "Gradient damage models in large deformation." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX085/document.

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Les modèles d'endommagement à gradient, aussi dénommés modèles à champs de phases, sont désormais largement utilisés pour modéliser la rupture fragile et ductile, depuis l'initiation de l'endommagement jusqu'à la propagation d'une fissure. Cependant, la majorité des études disponibles dans la littérature ne concerne que le cadre des petites déformations, et très peu d'études poussées ont été menées afin d'étudier leur pertinence dans un contexte de grandes déformations. Ce serait pourtant d'un intérêt primordial, notamment pour l'industrie pneumatique, qui deviendrait alors capable de prédire plus précisément l'initiation de l'endommagement dans ses structures.Dans la première partie de ce travail, nous établissons des solutions analytiques d'évolution de l'endommagement (homogène et localisée) pour des matériaux visqueux, en petites et en grandes déformations. En petites déformations, les modèles rhéologiques de Maxwell et Poynting-Thomson sont étudiés, et en grandes déformations, les modèles de Maxwell et Zener sont choisis. Une étude sur l'évolution de l'endommagement dans un cas purement hyperélastique est aussi menée.A cette première partie analytique succède une partie numérique, qui détaille l'implémentation des modèles d'endommagement à gradient dans des codes éléments finis en grandes déformations. De même qu'en petites déformations, une stratégie de minimisation alternée est adoptée pour résoudre successivement les problèmes d'endommagement et de déplacement. Le matériau suit une loi de Mooney-Rivlin quasi-incompressible, et une méthode mixte en déplacement-pression est utilisée. Des tests en 2D et 3D sont effectués, qui mettent en évidence la capacité des modèles à initier de l'endommagement en grandes déformations.Les modèles d'endommagement utilisés pour la seconde partie ne sont cependant capables d'initier de l'endommagement que dans les zones où la déformation est importante, c'est-à-dire dans les zones de forte contrainte déviatorique. Il a toutefois été montré que certains matériaux polymères, quasi-incompressibles, s'endommagent dans les zones de forte pression hydrostatique. Par conséquent, la recherche et l'étude d'un modèle d'endommagement capable d'initier de l'endommagement dans les zones de forte pression, pour des matériaux quasi-incompressibles lorsqu'ils sont sains, fait l'objet d'une troisième partie.Enfin, la croissance brusque de cavités dans un matériau hyperélastique, appelée phénomène de cavitation, est étudiée, ainsi que son interaction avec l'endommagement. Dans un premier temps, nous considérons la cavitation comme une simple bifurcation hyperélastique d'un matériau néo-hookéen compressible isotrope, et déterminons l'expression analytique de l'élongation critique pour laquelle la cavitation fait son apparition. Dans un second temps, nous montrons qu'il y a une compétition entre la cavitation et l'endommagement, et qu'en fonction de la valeur du ratio des élongations critiques respectives pour chaque phénomène, deux types de rupture apparaissent
Gradient damage models, also known as phase-field models, are now widely used to model brittle and ductile fracture, from the onset of damage to the propagation of a crack in various materials. Yet, they have been mainly studied in the framework of small deformation, and very few studies aims at proving their relevance in a finite deformation framework. This would be more helpful for the tyre industry that deals with very large deformation problems, and has to gain insight into the prediction of the initiation of damage in its structures.The first part of this work places emphasis on finding analytical solutions to unidimensional problems of damaging viscous materials in small and large deformation.In all the cases, the evolution of damage is studied, both in the homogeneous and localised cases. Having such solutions gives a suitable basis to implement these models and validate the numerical results.A numerical part naturally follows the first one, that details the specificities of the numerical implementation of these non local models in large deformation. In order to solve the displacement and damage problems, the strategy of alternate minimisation (or staggered algorithm) is used. When solved on the reference configuration, the damage problem is the same as in small deformation, and consists in a bound constraint minimisation. The displacement problem is non linear, and a mixed finite element method is used to solve a displacement-pressure problem. A quasi-incompressible Mooney-Rivlin law is used to model the behaviour of the hyperelastic material. Various tests in 2D and 3D are performed to show that gradient damage models are perfectly able to initiate damage in sound, quasi-incompressible structures, in large deformation.In the simulations depicted above, it should be noted that the damage laws combined to the hyperelastic potential results in an initiation of damage that takes place in zones of high deformation, or in other words, in zones of high deviatoric stress. However, in some polymer materials, that are known to be quasi-incompressible, it has been shown that the initiation of damage can take place in zones of high hydrostatic pressure. This is why an important aspect of the work consists in establishing a damage law such that the material be incompressible when there is no damage, and the pressure play a role in the damage criterion. Such a model is exposed in the third part.Finally, the last part focuses on the cavitation phenomenon, that can be understood as the sudden growth of a cavity. We first study it as a purely hyperelastic bifurcation, in order to get the analytical value of the critical elongation for which cavitation occurs, in the case of a compressible isotropic neo-hookean material submitted to a radial displacement. We show that there is a competition between the cavitation phenomenon and the damage, and that depending on the ratio of the critical elongation for damage and the critical elongation for cavitation, different rupture patterns can appear

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27

Boyce, Mary Cunningham. "Large inelastic deformation of glassy polymers." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14909.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaves 126-130.
by Mary Cunningham Boyce.
Ph.D.

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28

Tuzun, Aydin. "Large Deformation Analysis Of Flexible Multibody Systems." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614821/index.pdf.

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Large displacement and large strain problems of mechanical systems can be solved mainly by four methods. These are Floating Frame of Reference, Incremental Finite Element, Large Rotation Vector and Absolute Nodal Coordinate Formulations (ANCF). Due to exact rigid body representation, simple mass matrix structure and non-incremental formulation, ANCF is more convenient in analyzing flexible multibody systems. However, it is limited to problems with regular boundaries, currently. The aim of the thesis is to improve the current ANCF in order to handle various problems with irregular boundaries. For this purpose, firstly meshfree ANCF has been developed to analyze flexible multibody systems. Verification of the developed meshfree formulation has been performed for beam type structures and accurate results have been obtained. Then, &ldquo
ANCF with Virtual Element Mapping Method&rdquo
has been proposed to overcome the boundary problems of the current formulations. The proposed method has been implemented to plane stress, plane strain, plate/shell and 3D solid finite elements. Verification of the proposed method has been performed by using the patch test problems available in the literature. Besides, it has been verified by various flexible multibody problems with large deformations. Additionally, shape function polynomials for thin plate assumption have been derived. It is observed that developed formulations and methods can be useful not only for flexible multibody systems but also for structural mechanics problems subjected to large deformations and/or rotations. The proposed methods and formulations are more efficient than the current formulations in the literature due to extended shape limits of finite elements.

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29

Paradinas, Salsón Teresa. "Simplification, approximation and deformation of large models." Doctoral thesis, Universitat de Girona, 2011. http://hdl.handle.net/10803/51293.

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The high level of realism and interaction in many computer graphic applications requires techniques for processing complex geometric models. First, we present a method that provides an accurate low-resolution approximation from a multi-chart textured model that guarantees geometric fidelity and correct preservation of the appearance attributes. Then, we introduce a mesh structure called Compact Model that approximates dense triangular meshes while preserving sharp features, allowing adaptive reconstructions and supporting textured models. Next, we design a new space deformation technique called *Cages based on a multi-level system of cages that preserves the smoothness of the mesh between neighbouring cages and is extremely versatile, allowing the use of heterogeneous sets of coordinates and different levels of deformation. Finally, we propose a hybrid method that allows to apply any deformation technique on large models obtaining high quality results with a reduced memory footprint and a high performance.
L’elevat nivell de realisme i d’interacció requerit en múltiples aplicacions gràfiques fa que siguin necessàries tècniques pel processament de models geomètrics complexes. En primer lloc, presentem un mètode de simplificació que proporciona una aproximació precisa de baixa resolució d'un model texturat que garanteix fidelitat geomètrica i una correcta preservació de l’aparença. A continuació, introduïm el Compact Model, una nova estructura de dades que permet aproximar malles triangulars denses preservant els trets més distintius del model, permetent reconstruccions adaptatives i suportant models texturats. Seguidament, hem dissenyat *Cages, un esquema de deformació basat en un sistema de caixes multi-nivell que conserva la suavitat de la malla entre caixes veïnes i és extremadament versàtil, permetent l'ús de conjunts heterogenis de coordenades i diferents nivells de deformació. Finalment, proposem un mètode híbrid que permet aplicar qualsevol tècnica de deformació sobre models complexes obtenint resultats d’alta qualitat amb una memòria reduïda i un alt rendiment.

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30

Derian, Edward J. "Large deformation dynamic bending of composite beams." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45678.

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The large deformation response of composite beams subjected to a dynamic axial load was studied. The beams were loaded with a moderate amount of eccentricity to promote bending. The study was primarily experimental but some finite element results were obtained. Both the deformation and the failure of the beams were of interest. The static response of the beams was also studied in order to determine the difference between the static and dynamic failure. Twelve different laminate types were tested. The beams tested were 23 in. by 2 in. and generally 30 plies thick. The beams were loaded dynamically with a gravity-driven impactor traveling at 19.6 ft./sec. and quasi-static tests were done on identical beams in a displacement controlled manner. For laminates of practical interest, the failure modes under static and dynamic loadings were identical. Failure in most of the laminate types occurred in a single event involving 40% to 50% of the plies. However, failure in laminates with 30° or 15° off axis plies occurred in several events. All laminates exhibited bimodular properties. The compressive flexural moduli in some laminates was measured to be 1/2 the tensile flexural modulus. No simple relationship could be found among the measured ultimate failure strains of the different laminate types. Using empirically determined flexural properties, a finite element analysis was reasonably accurate in predicting the static and dynamic deformation response.

Master of Science

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31

Priestley, Daniel. "Modeling multidimensional large strain consolidation of tailings." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39809.

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Mine sites generate large volumes of tailings materials, requiring storage in tailings impoundments. Large strain consolidation of tailings materials represents a major factor in determining how a tailings impoundment will behave over time. Being able to accurately model these phenomena ensures that the effects of long term consolidation may be considered in the design of future tailings impoundments. SoilVision Systems has created an internal version of the SVOFFICE 2009 finite element modeling software capable of evaluating these scenarios. Prior to this research, preliminary benchmarks have been established, but the software had not yet been applied to multidimensional scenarios to benchmark the results. The goal of this research was to first benchmark the software against literature case studies. Following this, the software could then be applied to multidimensional tailings impoundments to study how the modeling could be performed and what factors require further consideration. Benchmarking of the software showed that the software is capable of recreating a wide variety of case studies from the literature. Further test were used to determine the effects of various material parameters on the material. Applications to multidimensional scenarios show that the software is capable of analyzing a wide variety of scenarios and considering numerous factors not found in other software packages. While the software does require additional functionality, it has been found to be a viable tool for examining multidimensional consolidation effects in tailings impoundments.

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32

Weise, Martina. "Elastic Incompressibility and Large Deformations." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-140113.

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This thesis investigates the numerical simulation of three-dimensional, mechanical deformation problems in the context of large deformations. The main focus lies on the prediction of non-linearly elastic, incompressible material. Based on the equilibrium of forces, we present the weak formulation of the large deformation problem. The discrete version can be derived by using linearisation techniques and an adaptive mixed finite element method. This problem turns out to be a saddle point problem that can, among other methods, be solved via the Bramble-Pasciak conjugate gradient method or the minimal residual algorithm. With some modifications the resulting simulation can be improved but we also address remaining limitations. Some numerical examples show the capability of the final FEM software. In addition, we briefly discuss the special case of linear elasticity with small deformations. Here we directly derive a linear weak formulation with a saddle point structure and apply the adaptive mixed finite element method. It is shown that the presented findings can also be used to treat the nearly incompressible case.

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33

Dressler, Bernhard. "Modélisation numérique des coques en grandes transformations : mise en oeuvre dans un environnement orienté objet." Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0522.

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Ce mémoire est consacré à la dynamique des coques en grandes rotations. La théorie bidimensionnelle des coques est déduite du principe des travaux virtuels d'un milieu continu tridimensionnel en introduisant la cinématique de Mindlin. On obtient un système d'équations non-linéaires qui est linéarise par rapport aux déplacements de la surface moyenne ainsi que par rapport aux paramètres de rotation. La paramétrisation des grandes rotations par le vecteur de rotation est comparée à la paramétrisation directe par la matrice de rotation. En vue d'une discrétisation en éléments finis isoparamétriques on utilise des objets tensoriels intrinsèques qui sont ramenés a une configuration de référence aplatie. Cette configuration aplatie est identifiée à l'élément de référence. En dehors d'une loi de comportement hyper élastique on présente deux lois élastoplastiques en grandes transformations supposant que les déformations locales restent petites. Les efforts résultants sont obtenus ou par une intégration numérique dans l'épaisseur ou a partir d'une loi de comportement globale qui est directement formulée en efforts résultants. L’implémentation numérique est effectuée dans un environnement de programmation orientée objet qui a été développe pour l'analyse non-linéaire par la méthode des éléments finis. En particulier, on regarde le rôle des grandes rotations dans le calcul de la matrice de rigidité tangente. Des résultats numériques confirment l'efficacité de cette approche.

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Evcim, Mehmet. "Large Deformation Analysis Of Shells Under Impulsive Loading." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611647/index.pdf.

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In this thesis large deformation behavior of shell structures under high intensity transient loading conditions is investigated by means of finite element method. For this purpose an explicit finite element program is developed with interactive user interface. The developed program deals with geometric and material nonlinearities which stem from large deformation elastic - plastic behavior. Results of the developed code are compared with the experimental data taken from the literature and simulation results of the commercial finite element program Ls-Dyna. Moreover, sensitivity study is carried out for mesh size, element type and material model parameters. After the comparison and verification of the obtained results, it is concluded that converged and reasonable results are achieved.

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35

Ma, Jianfeng. "Meshless method for modeling large deformation with elastoplasticity." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/402.

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36

Derisi, Bijan. "Development of thermoplastic composite tubes for large deformation." Thesis, Connect to online version, 2008. http://proquest.umi.com/pqdweb?did=1675143241&sid=1&Fmt=2&clientId=10306&RQT=309&VName=PQD.

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37

RIOS, GABRIEL EMILIANO BARRIENTOS. "NONLINEAR DYNAMICS OF FLEXIBLE STRUCTURES WITH LARGE DEFORMATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19770@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
É apresentado o modelo não-linear de barras proposto por Simo para o estudo do comportamento dinâmico de estruturas espaciais. A formulação das equações do movimento é feita em um sistema inercial de modo a simplificar o operador de inércia e o material é considerado como elástico linear. Carregamos não – conservativos são considerados de modo que a integração das equações é feita na forma fraca. As partes flexíveis, que são necessariamente estruturas unidimensionais, são descritas por um modelo de barras que generaliza os modelos clássicos de Euler-Bernouilli e de Timoshenko. Implementa-se um programa computacional baseado nesta teoria na linguagem Matlab. O modelo de barras discretiza-se espacialmente usando elementos finitos e integra-se o sistema de equações resultante linearizado usando o método de Newton-Raphson, associado ao esquema de integração de Newmark. Incorpora-se os efeitos de amortecimento interno e cargas seguidoras, assim como elementos lineares quadráticos. Se incorpora à programação o tratamento de juntas esféricas através do método de multiplicadores de Lagrange, que permitem estudar alguns tipos de sistemas de multicorpos flexíveis. O programa é testadopor uma série de exemplos e comparações com resultados clássicos para mostrar a sua versatilidade e também as limitações dos modelos clássicos. Também se apresenta o modelo usado no programa computacional SAMCEF, e mostra-se a potencialidade deste programa em base a uma série de exemplos que incluem problemas de flexibilidade e choque em sistemas multicorpos.
It is presented a theory to treat multibody problems with rigid or flexible parts that treats the overall motion and the deformations in the same way using na inertial reference frame. The essential part of the model is the treatment of nonlinear rods that are flexible parts of the multibody systems. A code was construcetd in the platform MATBLAB and it was widely tested thorough comparisons with results found in the literature that acted as benchmark problems. The results are very good.

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38

Eterovic, Adrian Luis. "Finite element analysis of large deformation contact problems." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13063.

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39

Wan, Deborah Jo-May 1974. "On elastic-plastic large deformation analysis of beams." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/10076.

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40

Abu-Saman, Awni. "Large plastic deformation and shear localization of crystals." Doctoral thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/4954.

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41

鄭榕明 and Yung-ming Cheng. "Large strain elasto-plastic soil-structure interaction analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31232528.

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42

Cheng, Yung-ming. "Large strain elasto-plastic soil-structure interaction analysis /." Hong Kong : University of Hong Kong, 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13212758.

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43

Traina, Zachary J. "A large strain piezoelectric microactuator by folding assembly." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39890.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (leaves 65-68).
In-plane amplification of thin film piezoelectric strain has been previously demonstrated using mechanical flexures fabricated at the micro scale. This new work presents a method by which that amplification can be increased, along with a method to reduce parasitic out of plane bending present in prior designs. Fabricated actuator triplets demonstrated peak unblocked displacement of 15 [mu]m, 3% total contraction by length, with an estimated blocking force of [approx.] -9.2 [mu]N. Methods of arraying one such cell massively in series and in parallel are also presented, with the long term goal of creating a large strain, efficient, and low power macro scale actuator from individual micro scale components.
by Zachary J. Traina.
S.M.

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44

Neal, Devin Michael. "Large-strain piezoelectric actuators using controlled structural buckling." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55282.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59-60).
Buckling is a highly nonlinear and singular phenomenon in thin beams, and is usually an undesired characteristic that must be prevented from occurring in engineered systems. Buckling, however, can be a useful mechanism for gaining extremely large displacement amplification, since a infinitesimal displacement in the axial direction of the beam may lead to a large deflection in the middle of the beam. This thesis presents a novel large-strain piezoelectric actuator exploiting the buckling of a structure with imbedded piezoelectric stack actuators. The realization of this buckling actuator began by rethinking the paradigm of where PZT stacks are placed in traditional flexure-based displacement amplification mechanisms. Although the free displacement of a PZT stack is only 0.1% of the stack length, the buckling mechanism can produce a large bipolar displacement that is approximately 150 times larger than the original PZT displacement. Furthermore, the structural buckling produces a pronounced nonlinearity in output impedance; the effective stiffness viewed from the output port varies as a function of output displacement, which can be a useful property for those applications where actuator stiffness needs to vary. Buckling is controlled with phased activation of the input units and either 1) a strategically placed redirecting stiffness or 2) multiple buckling units working in parallel.
by Devin Michael Neal.
S.M.

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45

Millereau, Pierre Michel. "Large Strain and Fracture of Multiple Network Elastomers." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066082/document.

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Durant ce travail, nous avons étudié les propriétés mécaniques et de fracture d'élastomères à réseaux multiples synthétisés par des étapes successives de gonflement/polymérisation inspirées de l'architecture moléculaire développée par Gong pour les doubles réseaux hydrogels. Une méthode de synthèse plus versatile a été utilisée pour varier de façon continue le pré-étirement isotrope du premier réseau λ0, qui contrôle le module d'Young et le durcissement. Dans le cas d'une dilution importante du premier réseau (<10%), une scission moléculaire apparaît à grande déformation dans le réseau pré-étiré sans rompre le matériau. Le taux de dilution contrôle la quantité d’endommagement et donc la pente de la courbe contrainte-déformation. Finalement, pour les systèmes les plus dilués (<3%), une striction est observée au-dessus d’un seuil de contrainte. Changer le taux de réticulant du premier réseau ou les monomères utilisés ont conduit par ailleurs à l’obtention de comportements mécaniques similaires. L’énergie de fracture Γ est une fonction croissante de λ0. Des techniques de visualisation locale comme la Corrélation d’Image Numérique et l’intégration de molécules méchanoluminescentes ont été utilisées pour décrire une zone d’endommagement en tête de fissure dont la taille augmente avec λ0. Enfin, le mécanisme de renforcement des élastomères à réseaux multiples a pu être partiellement décrit dans le contexte du modèle de Brown sur les doubles réseaux
We investigated systematically the mechanical and fracture properties of multiple network elastomers synthesized by successive swelling/polymerization steps inspired by the molecular architecture of Gong’s double network gels. A more versatile synthesis method was used to vary continuously the isotropic degree of prestretching λ0 of the first network resulting in a wider range of mechanical behaviours, where λ0 controls the Young’s modulus at small strain and the strain hardening at large strain. If the first network is diluted enough (<10%) molecular bond breakage occurs in this prestretched network at high strain while avoiding sample failure. The degree of dilution controls the amount of damage and therefore the slope of the stress-strain curve. Finally, for the most diluted systems (<3%), a yield stress and a necking phenomenon was observed. Changing the degree of crosslinking of the first network or the monomers used led to the same qualitative mechanical behaviour. The fracture energy Γ was shown to be an increasing function of λ0 however different regimes could be distinguished with macroscopic fracture occurring before or after bulk damage was detected. Visualisation techniques such as Digital Image Correlation and embedded mechanoluminescent molecules were used to map a damage zone in front of the crack tip, the size of which increased with λ0. Finally, the toughening mechanism of the multiple network elastomers could be understood in a nearly quantitative way within the framework of Brown's model of fracture of double network gels

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46

Bergström, Jörgen S. (Jörgen Stefan) 1969. "Large strain time-dependent behavior of elastomeric materials." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9794.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.
Includes bibliographical references (p. 248-254).
The mechanical behavior of elastomeric materials is known to be rate-dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response. Based on a detailed experimental investigation a new constitutive model for the time-dependence of unfilled elastomers has been developed. The foundation of the model is that the mechanical behavior can be decomposed into two parts: an equilibrium network corresponding to the state that is approached in long time stress relaxation tests; and a second network capturing the non-linear rate-dependent deviation from the equilibrium state. The time-dependence of the second network is further assumed to be governed by the reputational motion of molecules having the ability to significantly change conformation and thereby relaxing the overall stress state. To model the behavior of particle filled elastomers the newly developed constitutive framework is then extended to include filler interactions by amplification of the first strain invariant. In an effort to examine some of the assumptions that are common in the constitutive modeling of particle filled elastomers, a detailed series of micromechanical models were constructed using two- and three-dimensional finite elP.ment simulations. The results indicate that the effect of filler particles can be accurately predicted using stochastic three-dimensional simulations suggesting that successful modeling mainly requires a rigorous treatment of the composite nature of the microstructure and not molecular level concepts such as alteration of mobility or effective crosslinking density in the elastomeric phase of the material. A direct comparison between the new model and experimental data for a number of different elastomers the observed behavior.
by Jörgen S. Bergström.
Ph.D.

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47

Ouyang, Xin. "CONSTITUTIVE EQUATIONS OF RUBBER UNDER LARGE TENSILE STRAIN AND HIGH STRAIN RATES." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1154146622.

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48

Holsgrove, Stephen Clive. "Large deformation, large roation elasto-plastic shell analysis with particular application to tubular members and joints." Thesis, Kingston University, 1987. http://eprints.kingston.ac.uk/20511/.

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The ultimate strength assessment of steel tubular members is of the utmost importance to the design and maintenance of many structures including large offshore platforms. Ultimate strength assessments I using numerical solutions must model both nonlinear material and geometric behaviour. The latter must consider large displacements, very often large rotations, and possibly even large strains. These numerical solutions must be computationally efficient and be capable of running on generally available computer hardware, i.e. minicomputers. To achieve this efficiency, attention must be paid to programming considerations, and a new suite of data management modules has been developed and is described in this thesis, which minimise disk storage and speed program development. In addition, the structural modelling was carried out almost exclusively using the Semiiaaf thin shell element. The work described in this thesis considers most of the components which contribute to the numerical ultimate strength analysis of steel tubular members. Theoretically, attention has been focused in two areas, namely the geometric nonlinearity and the automatic solution of the resulting nonlinear equations. A detailed study has been carried out to understand fully the main methods of accounting for geometric nonlinearity from fundamentals of continuum mechanics. The study has considered both the Green-Lagrange and Logarithmic strain measures with a Total Lagrangian, Updated Lagrangian and Eulerian description of motion. These formulations have been included in the Semiiaaf shell element, firstly using a continuum mechanics based approach, and secondly using the more orthodox stress resultant approach. At all stages within the thesis attention is drawn to the effects of the approximations which have been made and their resulting limitations in the respective formulations. The solution of the nonlinear equations is also covered in detail using Newton-type algorithms coupled with line searches. The solution algorithms have been derived for a constrained environment where a modified version of the generalised arc-length constraint has been used. The inclusion of material nonlinearity has been well developed previously but has been included for completeness. To demonstrate the performance and limitations of the theory presented, several carefully chosen numerical examples have been included which include the analysis of tubular steel T and X joints connections and residual strength assessment of a dented pipeline riser. Where possible, results have been compared with experimental tests. The thesis concludes that for general engineering structures, the Total Lagrangian approach based on the stress resultant model gives good engineering results, even in the presence of moderately large rotations. Of the alternative formulations the Updated Lagrangian layered approach is probably the most effective for large rotations and small to moderate strains.

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Lei, Fulin. "Modeling of articular cartilage optimization, large deformation, and microstructure /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.21 Mb., 176 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3220728.

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Cheung, Chip. "Large deformation of textile fabrics using finite element method." Ohio : Ohio University, 1988. http://www.ohiolink.edu/etd/view.cgi?ohiou1182782321.

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Dissertations / Theses on the topic 'Large deformation large strain'

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