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Li, Yichen. "Phase-field Modeling of Phase Change Phenomena." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99148.
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The phase-field method has become a popular numerical tool for moving boundary problems in recent years. In this method, the interface is intrinsically diffuse and stores a mixing energy that is equivalent to surface tension. The major advantage of this method is its energy formulation which makes it easy to incorporate different physics. Meanwhile, the energy decay property can be used to guide the design of energy stable numerical schemes.
In this dissertation, we investigate the application of the Allen-Cahn model, a member of the phase-field family, in the simulation of phase change problems. Because phase change is usually accompanied with latent heat, heat transfer also needs to be considered. Firstly, we go through different theoretical aspects of the Allen-Cahn model for nonconserved interfacial dynamics. We derive the equilibrium interface profile and the connection between surface tension and mixing energy. We also discuss the well-known convex splitting algorithm, which is linear and unconditionally energy stable. Secondly, by modifying the free energy functional, we give the Allen-Cahn model for isothermal phase transformation. In particular, we explain how the Gibbs-Thomson effect and the kinetic effect are recovered. Thirdly, we couple the Allen-Chan and heat transfer equations in a way that the whole system has the energy decay property. We also propose a convex-splitting-based numerical scheme that satisfies a similar discrete energy law. The equations are solved by a finite-element method using the deal.ii library. Finally, we present numerical results on the evolution of a liquid drop in isothermal and non-isothermal settings. The numerical results agree well with theoretical analysis.Master of Science
Phase change phenomena, such as freezing and melting, are ubiquitous in our everyday life. Mathematically, this is a moving boundary problem where the phase front evolves based on the local temperature. The phase change is usually accompanied with the release or absorption of latent heat, which in turn affects the temperature. In this work, we develop a phase-field model, where the phase front is treated as a diffuse interface, to simulate the liquid-solid transition. This model is consistent with the second law of thermodynamics. Our finite-element simulations successfully capture the solidification and melting processes including the interesting phenomenon of recalescence.
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Loginova, Irina. "Phase-field modeling of diffusion controlled phase transformations." Doctoral thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3626.
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Diffusion controlled phase transformations are studied bymeans of the phase-field method. Morphological evolution ofdendrites, grains and Widmanst\"atten plates is modeled andsimulated.
Growth of dendrites into highly supersaturated liquids ismodeled for binary alloy solidification. Phase-field equationsthat involve both temperature and solute redistribution areformulated. It is demonstrated that while at low undercoolingheat diffusion does not affect the growth of dendrites, i.e.solidification is nearly isothermal, at high cooling rates thesupersaturation is replaced by the thermal undercooling as thedriving force for growth.
In experiments many crystals with different orientationsnucleate. The growth of randomly oriented dendrites, theirsubsequent impingement ant formation of grain boundaries arestudied in two dimensions using the FEM on adaptive grids.
The structure of dendrites is determined by growthconditions and physical parameters of the solidifying material.Effects of the undercooling and anisotropic surface energy onthe crystal morphology are investigated. Transition betweenseaweeds, doublons and dendrites solidifying out of puresubstance is studied and compared to experimental data. Two-and three-dimensional simulations are performed in parallel onadaptive and uniform meshes.
A phase-field method based on the Gibbs energy functional isformulated for ferrite to austenite phase transformation inFe-C. In combination with the solute drag model, transitionbetween diffusion controlled and massive transformations as afunction of C concentration and temperature is established byperforming a large number of one dimensional calculations withreal physical parameters. In two dimensions, growth ofWidmanstaetten plates is governed by the highly anisotropicsurface energy. It is found that the plate tip can beapproximated as sharp, in agreement with experiments.
Keywords:heat and solute diffusion, solidification,solid-solid phase transformation, microstructure, crystalgrowth, dendrite, grain boundary, Widmanstaetten plate,phase-field, adaptive mesh generation, FEM.
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Abdollahi, Amir. "Phase-field modeling of fracture in ferroelectric materials." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285833.
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The unique electro-mechanical coupling properties of ferroelectrics make them ideal materials for use in micro-devices as sensors, actuators and transducers. Nevertheless, because of the intrinsic brittleness of ferroelectrics, the optimal design of the electro-mechanical devices is strongly dependent on the understanding of the fracture behavior in these materials. Fracture processes in ferroelectrics are notoriously complex, mostly due to the interactions between the crack tip stress and electric fields and the localized switching phenomena in this zone (formation and evolution of domains of different crystallographic variants). Phase-field models are particularly interesting for such a complex problem, since a single partial differential equation governing the phase-field accomplishes at once (1) the tracking of the interfaces in a smeared way (cracks, domain walls) and (2) the modeling of the interfacial phenomena such as domain-wall energies or crack face boundary conditions. Such a model has no difficulty for instance in describing the nucleation of domains and cracks or the branching and merging of cracks. Furthermore, the variational nature of these models makes the coupling of multiple physics (electrical and mechanical fields in this case) very natural.
The main contribution of this thesis is to propose a phase-field model for the coupled simulation of the microstructure formation and evolution, and the nucleation and propagation of cracks in single crystal ferroelectric materials. The model naturally couples two existing energetic phase-field approaches for brittle fracture and ferroelectric domain formation and evolution. The finite element implementation of the theory is described. Simulations show the interactions between the microstructure and the crack under mechanical and electro-mechanical loadings. Another objective of this thesis is to encode different crack face boundary conditions into the phase-field framework since these conditions strongly affect the fracture behavior of ferroelectrics. The smeared imposition of these conditions are discussed and the results are compared with that of sharp crack models to validate the proposed approaches. Simulations show the effects of different conditions, electro-mechanical loadings and media filling the crack gap on the crack propagation and the microstructure of the material. In a third step, the coupled model is modified by introducing a crack non-interpenetration condition in the variational approach to fracture accounting for the asymmetric behavior in tension and compression. The modified model makes it possible to explain anisotropic crack growth in ferroelectrics under Vickers indentation loading. This model is also employed for the fracture analysis of multilayer ferroelectric actuators, which shows the potential of the model for future application. The coupled phase-field model is also extended to polycrystals by introducing realistic polycrystalline microstructures in the model. Inter- and trans-granular crack propagation modes are observed in the simulations. Finally and for completeness, the phase-field theory is extended for the simulation of conducting cracks and some preliminary simulations are also performed in three dimensions. Salient features of the crack propagation phenomenon predicted by the simulations of this thesis are directly compared with experimental observations.Los materiales ferroeléctricos poseen únicas propiedades electro-mecánicas y por eso se utilizan para los micro-dispositivos como sensores, actuadores y transductores. No obstante, debido a la fragilidad intrínseca de los ferroeléctricos, el diseño óptimo de los dispositivos electro-mecánicos es altamente dependiente de la comprensión del comportamiento de fractura en estos materiales. Los procesos de fractura en ferroeléctricos son notoriamente complejos, sobre todo debido a las interacciones entre campos de tensión y eléctricos y los fenómenos localizados en zona de fractura (formación y evolución de los dominios de las diferentes variantes cristalográficas). Los modelos de campo de fase son particularmente útiles para un problema tan complejo, ya que una sola ecuación diferencial parcial que gobierna el campo de fase lleva a cabo a la vez (1) el seguimiento de las interfaces de una manera suave (grietas, paredes de dominio) y (2) la modelización de los fenómenos interfaciales como las energías de la pared de dominio o las condiciones de las caras de grieta. Tal modelo no tiene ninguna dificultad, por ejemplo en la descripción de la nucleación de los dominios y las grietas o la ramificación y la fusión de las grietas. Además, la naturaleza variacional de estos modelos facilita el acoplamiento de múltiples físicas (campos eléctricos y mecánicos en este caso). La principal aportación de esta tesis es la propuesta de un modelo campo de fase para la simulación de la formación y evolución de la microestructura y la nucleación y propagación de grietas en materiales ferroeléctricos. El modelo aúna dos modelos de campo de fase para la fractura frágil y para la formación de dominios ferroeléctricos. La aplicación de elementos finitos a la teoría es descrita. Las simulaciones muestran las interacciones entre la microestructura y la fractura del bajo cargas mecánicas y electro-mecánicas. Otro de los objetivos de esta tesis es la codificación de diferentes condiciones de contorno de grieta porque estas condiciones afectan en gran medida el comportamiento de la fractura de ferroeléctricos. La imposición de estas condiciones se discuten y se comparan con los resultados de modelos clasicos para validar los modelos propuestos. Las simulaciones muestran los efectos de diferentes condiciones, cargas electro-mecánicas y medios que llena el hueco de la grieta en la propagación de las fisuras y la microestructura del material. En un tercer paso, el modelo se modifica mediante la introducción de una condición que representa el comportamiento asimétrico en tensión y compresión. El modelo modificado hace posible explicar el crecimiento de la grieta anisotrópica en ferroeléctricos. Este modelo también se utiliza para el análisis de la fractura de los actuadores ferroeléctricos, lo que demuestra el potencial del modelo para su futura aplicación. El modelo se extiende también a policristales mediante la introducción de microestructuras policristalinas realistas en el modelo. Modos de fractura inter y trans-granulares de propagación se observan en las simulaciones. Por último y para completar, la teoría del campo de fase se extiende para la simulación de las grietas conductivas y algunas simulaciones preliminares también se realizan en tres dimensiones. Principales características del fenómeno de la propagación de la grieta predicho por las simulaciones de esta tesis se comparan directamente con las observaciones experimentales.
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Asp, Grönhagen Klara. "Phase-field modeling of surface-energy driven processes." Doctoral thesis, KTH, Metallografi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11036.
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Surface energy plays a major role in many phenomena that are important in technological and industrial processes, for example in wetting, grain growth and sintering. In this thesis, such surface-energy driven processes are studied by means of the phase-field method. The phase-field method is often used to model mesoscale microstructural evolution in materials. It is a diffuse interface method, i.e., it considers the surface or phase boundary between two bulk phases to have a non-zero width with a gradual variation in physical properties such as energy density, composition and crystalline structure. Neck formation and coarsening are two important diffusion-controlled features in solid-state sintering and are studied using our multiphase phase-field method. Inclusion of Navier-Stokes equation with surface-tension forces and convective phase-field equations into the model, enables simulation of reactive wetting and liquid-phase sintering. Analysis of a spreading liquid on a surface is investigated and is shown to follow the dynamics of a known hydrodynamic theory. Analysis of important capillary phenomena with wetting and motion of two particles connected by a liquid bridge are studied in view of important parameters such as contact angles and volume ratios between the liquid and solid particles. The interaction between solute atoms and migrating grain boundaries affects the rate of recrystallization and grain growth. The phenomena is studied using a phase-field method with a concentration dependent double-well potential over the phase boundary. We will show that with a simple phase-field model it is possible to model the dynamics of grain-boundary segregation to a stationary boundary as well as solute drag on a moving boundary. Another important issue in phase-field modeling has been to develop an effective coupling of the phase-field and CALPHAD methods. Such coulping makes use of CALPHAD's thermodynamic information with Gibbs energy function in the phase-field method. With the appropriate thermodynamic and kinetic information from CALPHAD databases, the phase-field method can predict mictrostructural evolution in multicomponent multiphase alloys. A phase-field model coupled with a TQ-interface available from Thermo-Calc is developed to study spinodal decomposition in FeCr, FeCrNi and TiC-ZrC alloys.QC 20100622
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Bush, Joshua. "Phase Field Modeling of Thermotransport in Multicomponent Systems." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5152.
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Nuclear and gas turbine power plants, computer chips, and other devices and industries are running hotter than ever for longer than ever. With no apparent end to the trend, the potential arises for a phenomenon known as thermotransport to cause undesirable changes in these high temperature materials. The diffuse-interface method known as the phase-field model is a useful tool in the simulation and prediction of thermotransport driven microstructure evolution in materials. The objective of this work is to develop a phase-field model using practical and empirical properties of thermodynamics and kinetics for simulating the interdiffusion behavior and microstructural evolution of single and multiphase binary alloy system under composition and/or temperature gradients. Simulations are carried out using thermodynamics and kinetics of real systems, such as the U-Zr solid metallic fuel, with emphasis on the temperature dependencies of the kinetics governing diffusional interactions in single-phase systems and microstructural evolution in the presence of multiple driving forces in multi-phase systems.
A phase field model is developed describing thermotransport in the γ phase of the U-Zr alloy, a candidate for advanced metallic nuclear fuels. The model is derived using thermodynamics extracted from the CALPHAD database and temperature dependent kinetic parameters associated with thermotransport from the literature. Emphasis is placed upon the importance of the heat of transport, Q*, and atomic mobility, β. Temperature dependencies of each term are estimated from empirical data obtained directly from the literature, coupled with the textbook phenomenological formulae of each parameter. A solution is obtained via a finite volume approach with the aid of the FiPy® partial differential equation solver. Results of the simulations are described based on individual flux contributions from the gradients of both composition and temperature, and are found to be remarkably similar to experimental results from the literature.
In an additional effort the thermotransport behavior of a binary two-phase alloy is modeled, for the first time, via the phase-field method for a two-phase (γ + β) U-Zr system. The model is similarly built upon CALPHAD thermodynamics describing the γ and β phases of the U-Zr system and thermotransport parameters for the γ phase from literature. A parametric investigation of how the heats of transport for U and Zr in the β phase affect the redistribution is performed, and the interplay between system kinetics and thermodynamics are examined. Importantly, a strict control over the microstructure that is placed into the temperature gradient (at t=0) is used to eliminate the randomness associated with microstructural evolution from an initially unstable state, allowing an examination of exactly how the β phase thermotransport parameters affect the redistribution behavior of the system. Results are compared to a control scenario in which the system evolves only in the presence of thermodynamic driving forces, and the kinetic parameters that are associated with thermotransport are negligible. In contrast to the single-phase simulations, in the presence of a large thermodynamic drive for phase transformation and stability, the constituent redistribution caused by the thermotransport effect is comparatively smaller.ID: 031001396; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed June 3, 2013).; Thesis (M.S.M.S.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 50-53).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Asp, Grönhagen Klara. "Phase-field modeling of surface-energy driven processes." Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11036.
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Ullbrand, Jennifer. "Phase field modeling of Spinodal decomposition in TiAlN." Licentiate thesis, Linköpings universitet, Nanostrukturerade material, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-79611.
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TiAlN thin films are used commercially in the cutting tool industry as wear protection of the inserts. During cutting, the inserts are subjected to high temperatures (~ 900 ° C and sometimes higher). The objective of this work is to simulate the material behavior at such high temperatures. TiAlN has been studied experimentally at least for two decades, but no microstructure simulations have so far been performed. In this thesis two models are presented, one based on regular solution and one that takes into account clustering effects on the thermodynamic data. Both models include anisotropic elasticity and lattice parameters deviation from Vegard’s law. The input parameters used in the simulations are ab initio calculations and experimental data.Methods for extracting diffusivities and activation energies as well as Young’s modulus from phase field results are presented. Specifically, strains, von Mises stresses, energies, and microstructure evolution have been studied during the spinodal decomposition of TiAlN. It has been found that strains and stresses are generated during the decomposition i.e. von Mises stresses ranging between 5 and 7.5 GPa are typically seen. The stresses give rise to a strongly composition dependent elastic energy that together with the composition dependent gradient energy determine the decomposed microstructure. Hence, the evolving microstructure depends strongly on the global composition. Morphologies ranging from isotropic, round domains to entangled outstretched domains can be achievedby changing the Al content. Moreover, the compositional wavelength of the evolved domains during decomposition is also composition dependent and it decreases with increasing Al content. Comparing the compositional wavelength evolution extracted from simulations and small angle X-ray scattering experiments show that the decomposition of TiAlN occurs in two stages; first an initial stage of constant wavelength and then a second stage with an increasing wavelength are observed. This finding is characteristic for spinodal decomposition and offers conclusive evidence that an ordering transformation occurs. The Young’s modulus evolution for Ti 0.33 Al 0.67 N shows an increase of 5% to ~398 GPa during the simulated decomposition.
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Winkler, Benjamin [Verfasser], and Falko [Akademischer Betreuer] Ziebert. "Modeling crawling cellular motility with a phase field approach." Freiburg : Universität, 2019. http://d-nb.info/1193423104/34.
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Shen, Chen. "The fundamentals and applications of phase field method in quantitative microstructural modeling." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1080249965.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xx, 217 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Yunzhi Wang, Dept. of Materials Science and Engineering. Includes bibliographical references (p. 209-217).
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Omatuku, Emmanuel Ngongo. "Phase field modeling of dynamic brittle fracture at finite strains." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/30172.
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Fracture is the total or partial separation of an initially intact body through the propagation of one or several cracks. Computational methods for fracture mechanics are becoming increasingly important in dealing with the nucleation and propagation of these cracks. One method is the phase field approach, which approximates sharp crack discontinuities with a continuous scalar field, the so-called phase field. The latter represents the smooth transition between the intact and broken material phases. The evolution of the phase field due to external loads describes the fracture process. An original length scale is used to govern the diffusive approximation of sharp cracks. This method further employs a degradation function to account for the loss of the material stiffness during fracture by linking the phase field to the body’s bulk energy. To prevent the development of unrealistic crack patterns and interpenetration of crack faces under compression, this study uses the anisotropic split of the bulk energy, as proposed by Amor et al. [5], to model the different fracture behavior in tension, shear and compression. This research is part of a larger project aimed at the modeling of Antarctic sea ice dynamics. One aspect of this project is the modeling of the gradual break-up of the consolidated ice during spring. As a first step, this study reviews a phase field model used for dynamic brittle fracture at finite strains. Subsequently, this model is implemented into the in-house finite element software SESKA to solve the benchmark tension and shear tests on a single-edge notched block. The implementation adopts the so-called monolithic scheme, which computes the displacement and phase field solutions simultaneously, with a Newmark time integration scheme. The results of the solved problems demonstrate the capabilities of the implemented dynamic phase field model to capture the nucleation and propagation of cracks. They further confirm that the choice of length-scale and mesh size influences the solutions. In this regard, a small value of the length-scale converges to the sharp crack topology and yields a larger stress value. On the other hand, a large length-scale parameter combined with a too coarse mesh size can yield unrealistic results.
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Haas, Robert. "Modeling and analysis for general non-isothermal convective phase field systems." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983793018.
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Nigro, Claudio F. "Phase field modeling of flaw-induced hydride precipitation kinetics in metals." Licentiate thesis, Malmö högskola, Institutionen för materialvetenskap och tillämpad matematik (MTM), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-7787.
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Hydrogen embrittlement can manifest itself as hydride formation in structures when in contact with hydrogen-rich environments, e.g. in space and nuclear power applications. To supplant experimentation, modeling of such phenomena is beneficial to make life prediction reduce cost and increase the understanding. In the present work, two different approaches based on phase field theory are employed to study the precipitation kinetics of a second phase in a metal, with a special focus on the application of hydride formation in hexagonal close-packed metals. For both presented models, a single component of the non-conserved order parameter is utilized to represent the microstructural evolution. Throughout the modelling the total free energy of the system is minimized through the time-dependent Ginzburg-Landau equation, which includes a sixth order Landau potential in the first model, whereas one of fourth order is used for the second model. The first model implicitly incorporates the stress field emanating from a sharp crack through the usage of linear elastic fracture mechanics and the governing equation is solved numerically for both isotropic and anisotropic bodies by usage of the finite volume method. The second model is applied to plate and notched cantilever geometries, and it includes an anisotropic expansion of the hydrides that is caused by the hydride precipitation. For this approach, the mechanical and phase transformation aspects are coupled and solved simultaneously for an isotropic material using the finite element method. Depending on the Landau potential coefficients and the crack-induced hydrostatic stress, for the first model the second-phase is found to form in a confined region around the crack tip or in the whole material depending on the material properties. From the pilot results obtained with the second model, it is shown that the applied stress and considered anisotropic swelling induces hydride formation in preferential directions and it is localized in high stress concentration areas. The results successfully demonstrate the ability of both approaches to model second-phase formation kinetics that is triggered by flaw-induced stresses and their capability to reproduce experimentally observed hydride characteristics such as precipitation location, shape and direction.
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Cox, Jordan Jeffrey. "U-Pu-Zr Alloy Design by Ternary Potts-Phase Field Modeling." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5300.
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U-Pu-Zr nuclear fuels experience a redistribution of constituents and a number of phase transformations when subjected to the thermal gradient present in nuclear reactors. This redistribution and phase separation leads to several undesirable fuel performance issues. In an effort to better understand how different alloys compositions are affected by this thermal gradient, we utilize the recently introduced Hybrid Potts-phase Field Method to study the U-Pu-Zr system. The recently introduced Hybrid method couples microstructural and compositional evolutions of a system so that the two phenomena can be studied together rather than separately, as is frequently done. However, simulation of the U-Pu-Zr system required several adaptations to the modeling framework. First the model was adapted to incorporate a thermodynamic database for free energy calculations, as well as thermal diffusion (the Soret effect). These abilities were tested in the Al-Si system. Second, the modeling framework was expanded to simulate three component systems such that ternary U-Pu-Zr alloys could be studied.Simulations capture constituent redistribution and the appropriate phase transformations as compared to experimentally irradiated a U-16Pu-23Zr (at%) nuclear fuel. Additional simulations analyze constituent redistribution over the entire spectrum of U-Pu-Zr compositions. Analysis of these simulation results indicate alloys that are likely to experience minimal constituent redistribution and fewer phase boundaries, such that their fuel performance should be improved. The outcomes of the work include a coupled microstructural-compositional modeling framework for ternary alloys and suggestions of U-Pu-Zr alloys that could lead to improved fuel performance.
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Hou, Yue. "Computational Analysis of Asphalt Binder based on Phase Field Method." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/47783.
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The mechanical performance evaluation of asphalt binder has always been a challenging issue for pavement engineers. Recently, the Phase Field Method (PFM) has emerged as a powerful computational tool to simulate the microstructure evolution of asphalt binder. PFM analyzes the structure from the free energy aspect and can provide a view of the whole microstructure evolution process. In this dissertation, asphalt binder performance is analyzed by PFM in three aspects: first, the relationship between asphalt chemistry and performance is investigated. The components of asphalt are simplified to three: asphaltene, resin and oil. Simulation results show that phase separation will occur under certain thermal conditions and result in an uneven distribution of residual thermal stress. Second, asphalt cracking is analyzed by PFM. The traditional approach to analyze crack propagation is Classic Fracture Mechanics first proposed by Griffith, which needs to clearly depict the crack front conditions and may cause complex cracking topologies. PFM describes the microstructure using a phase-field variable which assumes positive one in the intact solid and negative one in the crack void. The fracture toughness is modeled as the surface energy stored in the diffuse interface between the intact solid and crack void. To account for the growth of cracks, a non-conserved Allen-Cahn equation is adopted to evolve the phase-field variable. The energy based formulation of the phase-field method handles the competition between the growth of surface energy and release of elastic energy in a natural way: the crack propagation is a result of the energy minimization in the direction of the steepest descent. Both the linear elasticity and phase-field equation are solved in a unified finite element frame work, which is implemented in the commercial software COMSOL. Different crack mode simulations are performed for validation. It was discovered that the onset of crack propagation agrees very well with the Griffith criterion and experimental results. Third, asphalt self-healing phenomenon is studied based on the Atomic Force Microscopy (AFM) technology. The self-healing mechanism is simulated in two ways: thermodynamic approach and mechanical approach. Cahn-Hilliard dynamics and Allen-Cahn dynamics are adopted, respectively.Ph. D.
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Bhogireddy, Venkata Sai Pavan Kumar. "Phase Field modeling of sigma phase transformation in duplex stainless steels : Using FiPy-Finite Volume PDE solver." Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161712.
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Duplex Stainless Steels (DSS) are used extensively in various industrial applications where the properties of both austenite and ferrite steels are required. Higher mechanical strength and superior corrosion resistance are the advantages of DSS. One of the main drawbacks for Duplex steels is precipitation of sigma phase and other intermetallic phases adversely affecting the mechanical strength and the corrosion behavior of the steels. The precipitation of these secondary phases and the associated brittleness can be due to improper heat treatment. The instability in the microstructure of Duplex stainless steels can be studied by understanding the phase transformations especially the ones involving sigma phase. To reduce the time and effort to be put in for experimental work, computational simulations are used to get an initial understanding on the phase transformations. The present thesis work is on the phase transformations involving sigma phase for Fe-Cr system and Fe-Cr-Ni system using theoretical approach in 1D and 2D geometries. A phase field model is implemented for the microstructural evolution in DSS in combination with thermodynamic data collected from the Thermo-Calc software. The Wheeler Boettinger McFadden (WBM) model is used for Gibbs energy interpolation of the system. FiPy- Finite volume PDE solver written in python is used to simulate the phase transformation conditions first in Fe-Cr system for ferrite-austenite and ferrite-sigma phase transformations. It is then repeated for Fe-Cr-Ni ternary system. In the present study a model was developed for deriving Gibbs energy expression for sigma phase based on the common tangent condition. This model can be used to describe composition constrained phases and stoichiometric phases using the WBM model in phase field modeling. Cogswell’s theory of using phase order variable instead of an interpolating polynomial in the expression for Gibbs energy of whole system is also tried.
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Schlueter, Alexander [Verfasser], and Charlotte [Akademischer Betreuer] Kuhn. "Phase Field Modeling of Dynamic Brittle Fracture / Alexander Schlueter ; Betreuer: Charlotte Kuhn." Kaiserslautern : Technische Universität Kaiserslautern, 2018. http://d-nb.info/116213397X/34.
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Zhang, Tao [Verfasser]. "Phase-field Modeling of Phase Changes and Mechanical Stresses in Electrode Particles of Secondary Batteries / Tao Zhang." Karlsruhe : KIT Scientific Publishing, 2021. http://nbn-resolving.de/urn:nbn:de:101:1-2021090215420514095759.
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Rao, Weifeng. "Computer Modeling and Simulation of Morphotropic Phase Boundary Ferroelectrics." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28493.
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Phase field modeling and simulation is employed to study the underlying mechanism of enhancing electromechanical properties in single crystals and polycrystals of perovskite-type ferroelectrics around the morphotropic phase boundary (MPB). The findings include:
(I) Coherent phase decomposition near MPB in PZT is investigated. It reveals characteristic multidomain microstructures, where nanoscale lamellar domains of tetragonal and rhombohedral phases coexist with well-defined crystallographic orientation relationships and produce coherent diffraction effects.
(II) A bridging domain mechanism for explaining the phase coexistence observed around MPBs is presented. It shows that minor domains of metastable phase spontaneously coexist with and bridge major domains of stable phase to reduce total system free energy, which explains the enhanced piezoelectric response around MPBs.
(III) We demonstrate a grain size- and composition-dependent behavior of phase coexistence around the MPBs in polycrystals of ferroelectric solid solutions. It shows that grain boundaries impose internal mechanical and electric boundary conditions, which give rise to the grain size effect of phase coexistence, that is, the width of phase coexistence composition range increases with decreasing grain sizes.
(IV) The domain size effect is explained by the domain wall broadening mechanism. It shows that, under electric field applied along the nonpolar axis, without domain wall motion, the domain wall broadens and serves as embryo of field-induced new phase, producing large reversible strain free from hysteresis.
(V) The control mechanisms of domain configurations and sizes in crystallographically engineered ferroelectric single crystals are investigated. It reveals that highest domain wall densities are obtained with intermediate magnitude of electric field applied along non-polar axis of ferroelectric crystals.
(VI) The domain-dependent internal electric field associated with the short-range ordering of charged point defects is demonstrated to stabilize engineered domain microstructure. The internal electric field strength is estimated, which is in agreement with the magnitude evaluated from available experimental data.
(VII) The poling-induced piezoelectric anisotropy in untextured ferroelectric ceramics is investigated. It is found that the maximum piezoelectric response in the poled ceramics is obtained along a macroscopic nonpolar direction; and extrinsic contributions from preferred domain wall motions play a dominant role in piezoelectric anisotropy and enhancement in macroscopic nonpolar direction.
(VIII) Stress effects on domain microstructure are investigated for the MPB-based ferroelectric polycrystals. It shows that stress alone cannot pole the sample, but can be utilized to reduce the strength of poling electric field.
(IX) The effects of compressions on hysteresis loops and domain microstructures of MPB-based ferroelectric polycrystals are investigated. It shows that longitudinal piezoelectric coefficient can be enhanced by compressions, with the best value found when compression is about to initiate the depolarization process.Ph. D.
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Perevoshchikova, Nataliya. "Modeling of austenite to ferrite transformation in steels." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0342/document.
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La thèse porte sur la modélisation de la transformation de l'austénite en ferrite dans les aciers en mettant l'accent sur les conditions thermodynamiques et cinétiques aux interfaces alpha/gamma en cours de croissance de la ferrite. Dans une première partie, la thèse se concentre sur la description des équilibres thermodynamiques entre alpha et gamma à l'aide de la méthode CalPhad. Nous avons développé un nouvel algorithme hybride combinant la construction d'une enveloppe convexe avec la méthode classique de Newton-Raphson. Nous montrons ses possibilités pour des aciers ternaire Fe-C-Cr et quaternaire Fe-C-Cr-Mo dans des cas particulièrement difficiles. Dans un second chapitre, un modèle à interface épaisse a été développé. Il permet de prédire l'ensemble du spectre des conditions à l'interface alpha/gamma au cours de la croissance de la ferrite, de l'équilibre complet au paraéquilibre avec des cas intermédiaires des plus intéressants. Nous montrons que de nombreux régimes cinétiques particuliers dans les systèmes Fe-C-X peuvent être prévus avec un minimum de paramètres d'ajustement, principalement le rapport entre les diffusivités de l'élément substitutionnel dans l'interface épaisse et dans le volume d'austénite. Le troisième chapitre porte sur l'étude d'un modèle de champ de phase. Une analyse approfondie des conditions à l'interface données par le modèle est réalisée en utilisant la technique des développements asymptotiques. En utilisant les connaissances fournies par cette analyse, le rôle de la mobilité intrinsèque d'interface sur la cinétique et les régimes de croissance est étudié, à la fois dans le cas simple d'alliages binaires Fe-C et dans le cas plus complexe d'alliages Fe-C-MnTransformation in steels focusing on the thermodynamic and kinetics conditions at the alpha/gamma interfaces during the ferrite growth. The first chapter deals with the determination of thermodynamic equilibria between alpha and gamma with CalPhad thermodynamic description. We have developed a new hybrid algorithm combining the construction of a convex hull to the more classical Newton-Raphson method to compute two phase equilibria in multicomponent alloys with two sublattices. Its capabilities are demonstrated on ternary Fe-C-Cr and quaternary Fe-C-Cr-Mo steels. In the second chapter, we present a thick interface model aiming to predict the whole spectrum of conditions at an alpha/gamma interface during ferrite growth, from full equilibrium to paraequilibrium with intermediate cases as the most interesting feature. The model, despite its numerous simplifying assumptions to facilitate its numerical implementation, allows to predict some peculiar kinetics in Fe-C-X systems with a minimum of fitting parameters, mainly the ratio between the diffusivities of the substitutional element inside the thick interface and in bulk austenite. The third chapter deals with the phase field model of austenite to ferrite transformation in steels. A thorough analysis on the conditions at the interface has been performed using the technique of matched asymptotic expansions. Special attention is given to clarify the role of the interface mobility on the growth regimes both in simple Fe-C alloys and in more complex Fe-C-Mn alloys
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Zhu, Benqiang. "Phase-field modeling of microstructure evolution in low-carbon steels during intercritical annealing." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52176.
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Intercritical annealing is used widely in the steel industry to produce advanced high strength steels for automotive applications, e.g. dual-phase steels. A phase-field model is develop to describe microstructure evolution during intercritical annealing of low-carbon steels. The phase-field model consists of individual sub-models for ferrite recrystallization, austenite formation and austenite to ferrite transformation. In particular, a Gibbs-energy dissipation model is coupled to the phase-field model to describe the effects of solutes on migration of austenite/ferrite interfaces. The model is applied to a low-carbon steel with a cold-rolled pearlite/ferrite microstructure suitable for industrial production of dual-phase steels (DP600 grade). The sub-model parameters, e.g. nucleation parameters and interface mobilities, are tuned using experimental data. The interaction of concurrent ferrite recrystallization and austenite formation is investigated using the developed model. The simulation results reveal that ferrite recrystallization can be inhibited by the pinning effect of austenite particles and concurrent ferrite recrystallization can lead to intragranular distribution of austenite in the final microstructure. The transition of austenite morphology from a network structure to a banded structure with increasing heating rates is replicated by the phase-field model. The model is validated using a simulated industrial intercritical-annealing cycle. Moreover, the developed phase-field model is used to describe cyclic phase transformations in the intercritical region for a plain-carbon steel and a manganese-alloyed low-carbon steel. The consideration of Gibbs-energy dissipation in the phase-field model rationalizes the existence of stagnant stages during cyclic phase transformations in the manganese-alloyed low-carbon steel. In summary, the developed model provides a single tool that is able to describe various physical phenomena occurring in an entire intercritical-annealing cycle. Phase-field modeling can be a promising approach for developing process models for advanced steels in the future.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Diewald, Felix [Verfasser], and Ralf [Akademischer Betreuer] Müller. "Phase Field Modeling of Static and Dynamic Wetting / Felix Diewald ; Betreuer: Ralf Müller." Kaiserslautern : Technische Universität Kaiserslautern, 2020. http://d-nb.info/1205314733/34.
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Yeddu, Hemantha Kumar. "Martensitic Transformations in Steels : A 3D Phase-field Study." Doctoral thesis, KTH, Metallografi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95316.
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Martensite is considered to be the backbone of the high strength of many commercial steels. Martensite is formed by a rapid diffusionless phase transformation, which has been the subject of extensive research studies for more than a century. Despite such extensive studies, martensitic transformation is still considered to be intriguing due to its complex nature. Phase-field method, a computational technique used to simulate phase transformations, could be an aid in understanding the transformation. Moreover, due to the growing interest in the field of “Integrated computational materials engineering (ICME)”, the possibilities to couple the phase-field method with other computational techniques need to be explored. In the present work a three dimensional elastoplastic phase-field model, based on the works of Khachaturyan et al. and Yamanaka et al., is developed to study the athermal and the stress-assisted martensitic transformations occurring in single crystal and polycrystalline steels. The material parameters corresponding to the carbon steels and stainless steels are considered as input data for the simulations. The input data for the simulations is acquired from computational as well as from experimental works. Thus an attempt is made to create a multi-length scale model by coupling the ab-initio method, phase-field method, CALPHAD method, as well as experimental works. The model is used to simulate the microstructure evolution as well as to study various physical concepts associated with the martensitic transformation. The simulation results depict several experimentally observed aspects associated with the martensitic transformation, such as twinned microstructure and autocatalysis. The results indicate that plastic deformation and autocatalysis play a significant role in the martensitic microstructure evolution. The results indicate that the phase-field simulations can be used as tools to study some of the physical concepts associated with martensitic transformation, e.g. embryo potency, driving forces, plastic deformation as well as some aspects of crystallography. The results obtained are in agreement with the experimental results. The effect of stress-states on the stress-assisted martensitic microstructure evolution is studied by performing different simulations under different loading conditions. The results indicate that the microstructure is significantly affected by the loading conditions. The simulations are also used to study several important aspects, such as TRIP effect and Magee effect. The model is also used to predict some of the practically important parameters such as Ms temperature as well as the volume fraction of martensite formed. The results also indicate that it is feasible to build physically based multi-length scale model to study the martensitic transformation. Finally, it is concluded that the phase-field method can be used as a qualitative aid in understanding the complex, yet intriguing, martensitic transformations.QC 20120525
Hero-m
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Ankit, Kumar [Verfasser]. "Phase-field modeling of microstructural pattern formation in alloys and geological veins / Kumar Ankit." Karlsruhe : KIT Scientific Publishing, 2016. http://www.ksp.kit.edu.
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Alaimo, Francesco [Verfasser], Axel [Gutachter] Voigt, and Igor [Gutachter] Aronson. "Phase Field Crystal Modeling of Active Matter / Francesco Alaimo ; Gutachter: Axel Voigt, Igor Aronson." Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226900887/34.
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Zhang, Tao [Verfasser], and M. [Akademischer Betreuer] Kamlah. "Phase-field Modeling of Phase Changes and Mechanical Stresses in Electrode Particles of Secondary Batteries / Tao Zhang ; Betreuer: M. Kamlah." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1193126711/34.
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Zuo, Yinan [Verfasser], Bai-Xiang [Akademischer Betreuer] Xu, and Yuri [Akademischer Betreuer] Genenko. "Phase field modeling of ferroelectrics with point defects / Yinan Zuo ; Bai-Xiang Xu, Yuri Genenko." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1122286201/34.
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Handler, Matthew Dane. "Development of stable operator splitting numerical algorithms for phase-field modeling and surface diffusion applications." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35068.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (leaves 35-37).
Implicit, explicit and spectral algorithms were used to create Allen-Cahn and Cahn-Hilliard phase field models. Individual terms of the conservation equations were approached by different methods using operator splitting techniques found in previous literature. In addition, dewetting of gold films due to surface diffusion was modeled to present the extendability and efficiency of the spectral methods derived. The simulations developed are relevant to many real systems and are relatively light in computational load because they take large time steps to drive the model into equilibrium. Results were analyzed by their relevancy to real world applications and further work in this field is outlined.
by Matthew Dane Handler.
S.B.
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Wei, Xiupeng. "Multiscale modeling and simulation of material phase change problems: ice melting and copper crystallization." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/904.
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The primary objective of this work is to propose a state-of-the-art physics based multiscale modeling framework for simulating material phase change problems. Both ice melting and copper crystallization problems are selected to demonstrate this multiscale modeling and simulation. The computational methods employed in this thesis include: classical molecular dynamics, finite element method, phase-field method, and multiscale (nano/micro coupling) methods.
Classical molecular dynamics (MD) is a well-known method to study material behaviors at atomic level. Due to the limit of MD, it is not realistic to provide a complete molecular model for simulations at large length and time scales. Continuum methods, including finite element methods, should be employed in this case.
In this thesis, MD is employed to study phase change problems at the nanoscale. In order to study material phase change problems at the microscale, a thermal wave method one-way coupling with the MD and a phase-field method one-way coupling with MD are proposed. The thermal wave method is more accurate than classical thermal diffusion for the study of heat transfer problems especially in crystal based structures. The second model is based on the well-known phase-field method. It is modified to respond to the thermal propagation in the crystal matrix by the thermal wave method, as well as modified to respond to temperature gradients and heat fluxes by employing the Dual-Phase-Lag method. Both methods are coupled with MD to obtain realistic results.
It should be noted that MD simulations can be conducted to obtain material/thermal properties for microscopic and/or macroscopic simulations for the purpose of hierarchical/sequential multiscale modeling. These material parameters include thermal conductivity, specific heat, latent heat, and relaxation time. Other type of interfacial parameters that occur during the phase change process, such as nucleus shape, interfacial energy, interfacial thickness, etc., are also obtained by MD simulation since these have so far been too difficult to measure experimentally.
I consider two common phase change phenomena, ice melting and copper crystallization, in this thesis. For the case of ice melting, MD is first employed to study its phase change process and obtain thermal properties of ice and water. Several potential models are used. I conduct simulations of both bulk ice and ice/water contacting cases. It is found that various potential models result in similar melting phenomena, especially melting speed. Size effects are also studied and it is found that the melting time is longer for larger bulk ice segments but that the average melting speed is size dependent. There is no size effect for the melting speed at ice/water interface at the nanoscale if the same temperature gradient is applied. The melting speed of ice should depend on the temperature gradient. To study ice melting at the microscale, the thermal wave model is employed with parameters obtained from MD simulations. It is found that ice melting speed is scale, for both length scale and time scale, dependent.
For the case of copper crystallization, an EAM potential is first employed to conduct MD simulations for studying the copper crystallization process at the nanoscale. I obtain thermal properties and interfacial parameters, including thermal diffusion coefficient, latent heat, relaxation time, interfacial thickness, interfacial energy and the anisotropy coefficients, and nucleus shape etc. A central symmetry parameter is used to identify an atom in solid state or liquid state. And then an initial nucleus shape is obtained and used as the input for microscale simulation, in which the phase-field method is used to study copper crystallization at the microscale.
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Shi, Rongpei. "Variant Selection during Alpha Precipitation in Titanium Alloys- A Simulation Study." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397655766.
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Rathi, Pankaj Jaiprakash. "Theoretical Modeling of Morphology Development in Blends of Semicrystalline Polymers Undergoing Photopolymerization." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1251397199.
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Wang, Shuai [Verfasser], Bai-Xiang [Akademischer Betreuer] Xu, and Wolfgang [Akademischer Betreuer] Kleemann. "Phase-Field Modeling of Relaxor Ferroelectrics and Related Composites / Shuai Wang ; Bai-Xiang Xu, Wolfgang Kleemann." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1177241668/34.
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Salman, Oguz Umut. "Modeling of spatio-temporal dynamics and patterning mechanisms of martensites by phase-field and lagrangian methods." Paris 6, 2009. http://www.theses.fr/2009PA066221.
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Paranjape, Harshad Madhukar. "Modeling of Shape Memory Alloys: Phase Transformation/Plasticity Interaction at the Nano Scale and the Statistics of Variation in Pseudoelastic Performance." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417605178.
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Ankit, Kumar [Verfasser], and B. [Akademischer Betreuer] Nestler. "Phase-field modeling of microstructural pattern formation in alloys and geological veins / Kumar Ankit. Betreuer: B. Nestler." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1081722258/34.
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Fromm, Bradley S. "Linking phase field and finite element modeling for process-structure-property relations of a Ni-base superalloy." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45789.
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Establishing process-structure-property relationships is an important objective in the paradigm of materials design in order to reduce the time and cost needed to develop new materials. A method to link phase field (process-structure relations) and microstructure-sensitive finite element (structure-property relations) modeling is demonstrated for subsolvus polycrystalline IN100. A three-dimensional (3D) experimental dataset obtained by orientation imaging microscopy performed on serial sections is utilized to calibrate a phase field model and to calculate inputs for a finite element analysis. Simulated annealing of the dataset realized through phase field modeling results in a range of coarsened microstructures with varying grain size distributions that are each input into the finite element model. A rate dependent crystal plasticity constitutive model that captures the first order effects of grain size, precipitate size, and precipitate volume fraction on the mechanical response of IN100 at 650°C is used to simulate stress-strain behavior of the coarsened polycrystals. Model limitations and ideas for future work are discussed.
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Veluvali, Pavan Laxmipathy [Verfasser], and B. [Akademischer Betreuer] Nestler. "Phase-field modeling of unidirectionally solidified microstructures under diffusive-convective regime / Pavan Laxmipathy Veluvali ; Betreuer: B. Nestler." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1238148123/34.
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Bhowmick, Sauradeep. "Advanced Smoothed Finite Element Modeling for Fracture Mechanics Analyses." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623240613376967.
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Tahir, Abdul Malik. "Alloy element redistribution during sintering of powder metallurgy steels." Doctoral thesis, KTH, Fysiokemisk strömningsmekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145251.
Full textAbstract:
Homogenization of alloying elements is desired during sintering of powder metallurgy components. The redistribution processes such as penetration of liquid phase into the interparticle/grain boundaries of solid particles and subsequent solid-state diffusion of alloy element(s) in the base powder, are important for the effective homogenization of alloy element(s) during liquid phase sintering of the mixed powders. The aim of this study is to increase the understanding of alloy element redistribution processes and their effect on the dimensional properties of the compact by means of numerical and experimental techniques. The phase field model coupled with Navier-Stokes equations is used for the simulations of dynamic wetting of millimeter- and micrometer-sized metal drops and liquid phase penetration into interparticle boundaries. The simulations of solid particle rearrangement under the action of capillary forces exerted by the liquid phase are carried out by using the equilibrium equation for a linear elastic material. Thermodynamic and kinetic calculations are performed to predict the phase diagram and the diffusion distances respectively. The test materials used for the experimental studies are three different powder mixes; Fe-2%Cu, Fe-2%Cu-0.5%C, and Fe-2%(Cu-2%Ni-1.5%Si)-0.5%C. Light optical microscopy, energy dispersive X-ray spectroscopy and dilatometry are used to study the microstructure, kinetics of the liquid phase penetration, solid-state diffusion of the Cu, and the dimensional changes during sintering. The wetting simulations are verified by matching the spreading experiments of millimeter-sized metal drops and it is observed that wetting kinetics is much faster for a micrometer-sized drop compared to the millimeter-sized drop. The simulations predicted the liquid phase penetration kinetics and the motion of solid particles during the primary rearrangement stage of liquid phase sintering in agreement with the analytical model. Microscopy revealed that the C addition delayed the penetration of the Cu rich liquid phase into interparticle/grain boundaries of Fe particles, especially into the grain boundaries of large Fe particles, and consequently the Cu diffusion in Fe is also delayed. We propose that the relatively lower magnitude of the sudden volumetric expansion in the master alloy system could be due to the continuous melting of liquid forming master alloy particles.QC 20140515
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Cajuhi, Tuanny Verfasser], Lorenzis Laura [Akademischer Betreuer] De, and Pietro [Akademischer Betreuer] [Lura. "Fracture in porous media : phase-field modeling, simulation and experimental validation / Tuanny Cajuhi ; Laura De Lorenzis, Pietro Lura." Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1180601521/34.
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Sridhar, Ashish [Verfasser], and Marc-André [Akademischer Betreuer] Keip. "Phase-field modeling of microstructure and fracture evolution in magneto-electro-mechanics / Ashish Sridhar ; Betreuer: Marc-André Keip." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/1232727903/34.
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Aldakheel, Fadi [Verfasser], and Christian [Akademischer Betreuer] Miehe. "Mechanics of nonlocal dissipative solids : gradient plasticity and phase field modeling of ductile fracture / Fadi Aldakheel ; Betreuer: Christian Miehe." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1118370228/34.
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Hizir, Fahri Erinc. "Phase-field modeling of liquids splitting between separating surfaces and its application to high-resolution roll-based printing technologies." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104230.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages ).
In roll-based printing systems, controlled release of liquid ink to the substrate surface is achieved through the transport of the liquid ink through a series of ink transfer rollers in the form of splitting liquid bridges. An in-depth understanding of the liquid transport process through the ink transfer rollers is essential for advancing the roll-based printing technology and achieving the highest quality printing. In this study, the phase-field method is investigated to characterize the liquid bridges in roll-based printing systems. Phase-field models of two-phase flow systems are being used increasingly often in a variety of applications ranging from microfluidics to turbulent flows. However, there are limited implementations of the phase-field method to simulate the liquid ink transport in roll-based printing systems. There are advantages of the phase-field method over other methods that are generally used for simulating the liquid transport in roll-based printing systems such as the volume of fluid method and the moving mesh methods. This study demonstrates that the phase-field method is an effective tool to simulate the liquid ink transport in roll-based printing systems that facilitates the treatment of certain characteristics of the ink flows such as moving and deforming interfaces, topology changes, and slipping contact lines. In the phase-field simulations described in this study, the liquid ink transport between the rollers is approximated as the stretching and splitting of liquid bridges with pinned or moving contact lines between vertically separating surfaces. The interface separating the liquid and the surrounding air is represented as a diffuse interface with finite thickness across which the two phases mix. First, the simulation conditions that yield accurate results are determined by examining the effect of the phase-field parameters and the mesh characteristics on the simulation results. The simulation results show that a sharp interface limit is approached when the capillary width is decreased keeping the mobility proportional to the capillary width squared. This limit best represents real interfaces having molecular thickness in the micron-scale flows investigated. Close to the sharp interface limit, the mobility changes over a specified range are observed to have no significant influence on the simulation results. The computational mesh is segmented into regions of varying mesh fineness or adaptive mesh refinement is implemented to reduce the computational cost of resolving thin interfaces in the simulations. The simulation results are validated against data reported in existing studies of liquid ink transport in roll-based printing systems for selected capillary width and mobility values. Next, the liquid ink transport from the axisymmetric cells on the surface an ink-metering roller to the surface of stamp features is simulated. The function of the cells on an ink-metering roller is to control the amount of liquid ink delivered to the stamp surface. The resolution of printing is limited by the width of the cell openings, since uniform inking of the stamp requires the width of the cell openings to be smaller than the size of the stamp features. The cell geometries explored in the simulations are selected to enable printing with higher resolution than the current industry standards. Increasing the resolution of printing would improve the performance of printed products and expand their range of functionality. The results of the simulations indicate that under negligible inertial effects and in the absence of gravity, the amount of liquid ink transferred from a cell with low surface wettability to a stamp with high surface wettability increases as the cell sidewall steepness and the cell surface wettability decrease, and the stamp surface wettability and the capillary number increase. The amount of liquid ink removed from the cell does not change significantly as the cell depth increases above a certain value. High-resolution printing strategies, which indicate how the printing parameters should be manipulated to more precisely control the printed layer thickness, to eliminate printing defects, and to minimize cell clogging, are derived by analyzing the simulation results. The cells with different sidewall inclination angles are used to represent the cells with irregular surface topography on novel materials and novel roller designs that could be used for stamp inking during high-resolution roll-based printing, such as the pores on porous materials and the cells fabricated with poor control over cell geometry due to manufacturing difficulties at small length scales. The variations in the printed layer thickness with the cell sidewall inclination angle is found to be significant (~10-100 nm for cells with 2-[mu]m opening width) indicating that the variations in cell geometry should be minimized when designing advanced rollers for use in high-resolution roll-based printing.
by Fahri Erinc Hizir.
Ph. D.
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Ma, Ning. "Theory and modeling of microstructural evolution in polycrystalline materials solute segregation, grain growth and phase transformation /." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1111774761.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xvii, 181 p.; also includes graphics (some col.). Includes bibliographical references (p. 168-181). Available online via OhioLINK's ETD Center
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Zhao, Ying [Verfasser], Bai-Xiang [Akademischer Betreuer] Xu, and Kerstin [Akademischer Betreuer] Weinberg. "Phase-Field Modeling of Electro-Chemo-Mechanical Behavior of Li-ion Battery Electrodes / Ying Zhao ; Bai-Xiang Xu, Kerstin Weinberg." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1136719350/34.
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Mennerich, Christian [Verfasser]. "Phase-field modeling of multi-domain evolution in ferromagnetic shape memory alloys and of polycrystalline thin film growth / Christian Mennerich." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.
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Santoki, Jay [Verfasser], and B. [Akademischer Betreuer] Nestler. "Phase-field modeling on the diffusion-driven processes in metallic conductors and lithium-ion batteries / Jay Santoki ; Betreuer: B. Nestler." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1225401070/34.
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Vakili, Samad [Verfasser], Fathollah [Gutachter] Varnik, and Dierk [Gutachter] Raabe. "Multi-phase-field modeling of structure formation in metallic foams / Samad Vakili ; Gutachter: Fathollah Varnik, Dierk Raabe ; Fakultät für Maschinenbau." Bochum : Ruhr-Universität Bochum, 2021. http://d-nb.info/1228627487/34.
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Schänzel, Lisa-Marie [Verfasser], and Christian [Akademischer Betreuer] Miehe. "Phase field modeling of fracture in rubbery and glassy polymers at finite thermo-viscoelastic deformations / Lisa-Marie Schänzel. Betreuer: Christian Miehe." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2015. http://d-nb.info/1069107409/34.
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Li, Tianyi. "Gradient-damage modeling of dynamic brittle fracture : variational principles and numerical simulations." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX042/document.
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Une bonne tenue mécanique des structures du génie civil en béton armé sous chargements dynamiques sévères est primordiale pour la sécurité et nécessite une évaluation précise de leur comportement en présence de propagation dynamique de fissures. Dans ce travail, on se focalise sur la modélisation constitutive du béton assimilé à un matériau élastique-fragile endommageable. La localisation des déformations sera régie par un modèle d'endommagement à gradient où un champ scalaire réalise une description régularisée des phénomènes de rupture dynamique. La contribution de cette étude est à la fois théorique et numérique. On propose une formulation variationnelle des modèles d'endommagement à gradient en dynamique. Une définition rigoureuse de plusieurs taux de restitution d'énergie dans le modèle d'endommagement est donnée et on démontre que la propagation dynamique de fissures est régie par un critère de Griffith généralisé. On décrit ensuite une implémentation numérique efficace basée sur une discrétisation par éléments finis standards en espace et la méthode de Newmark en temps dans un cadre de calcul parallèle. Les résultats de simulation de plusieurs problèmes modèles sont discutés d'un point de vue numérique et physique. Les lois constitutives d'endommagement et les formulations d'asymétrie en traction et compression sont comparées par rapport à leur aptitude à modéliser la rupture fragile. Les propriétés spécifiques du modèle d'endommagement à gradient en dynamique sont analysées pour différentes phases de l'évolution de fissures : nucléation, initiation, propagation, arrêt, branchement et bifurcation. Des comparaisons avec les résultats expérimentaux sont aussi réalisées afin de valider le modèle et proposer des axes d'améliorationIn civil engineering, mechanical integrity of the reinforced concrete structures under severe transient dynamic loading conditions is of paramount importance for safety and calls for an accurate assessment of structural behaviors in presence of dynamic crack propagation. In this work, we focus on the constitutive modeling of concrete regarded as an elastic-damage brittle material. The strain localization evolution is governed by a gradient-damage approach where a scalar field achieves a smeared description of dynamic fracture phenomena. The contribution of the present work is both theoretical and numerical. We propose a variationally consistent formulation of dynamic gradient damage models. A formal definition of several energy release rate concepts in the gradient damage model is given and we show that the dynamic crack tip equation of motion is governed by a generalized Griffith criterion. We then give an efficient numerical implementation of the model based on a standard finite-element spatial discretization and the Newmark time-stepping methods in a parallel computing framework. Simulation results of several problems are discussed both from a computational and physical point of view. Different damage constitutive laws and tension-compression asymmetry formulations are compared with respect to their aptitude to approximate brittle fracture. Specific properties of the dynamic gradient damage model are investigated for different phases of the crack evolution: nucleation, initiation, propagation, arrest, kinking and branching. Comparisons with experimental results are also performed in order to validate the model and indicate its further improvement
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Nguyen, Thanh Tung. "Modeling of complex microcracking in cement based materials by combining numerical simulations based on a phase-field method and experimental 3D imaging." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1152/document.
Full textAbstract:
Une approche combinant simulation numérique et expérimentation est développée pour modéliser la microfissuration complexe dans des matériaux hétérogènes cimentaires. Le modèle numérique proposé a permis de prévoir précisément en 3D l'initiation et la propagation des microfissures à l'échelle de la microstructure réelle d'un échantillon soumis à un chargement de compression. Ses prévisions ont été validées par une comparaison directe avec le réseau de fissures réel caractérisé par des techniques d'imagerie 3D. Dans une première partie, nous développons et testons les outils de simulation numérique. Plus précisément, la méthode de champ de phase est appliquée pour simuler la microfissuration dans des milieux fortement hétérogènes et ses avantages pour ce type de modélisation sont discutés. Ensuite, une extension de cette méthode est proposée pour tenir compte d'un endommagement interfacial, notamment aux interfaces inclusion/matrice. Dans une deuxième partie, les méthodes expérimentales utilisées et développées au cours de cette thèse sont décrites. Les procédures utilisées pour obtenir l'évolution du réseau de fissures 3D dans les échantillons à l'aide de microtomographie aux rayons X et d'essais mécaniques in-situ sont présentées. Ensuite, les outils de traitement d'image utilisant la corrélation d'images volumiques, pour extraire les fissures des images en niveaux de gris avec une bonne précision, sont détaillés. Dans une troisième partie, les prévisions du modèle numérique sons comparées avec les données expérimentales d'un matériau modèle en billes de polystyrène expansé intégrées dans une matrice de plâtre dans un premier temps, et, dans un second temps, d'un béton léger plus complexe. Plus précisément, nous utilisons les données expérimentales pour identifier les paramètres microscopiques inconnus par une approche inverse, et utilisons les déplacements expérimentaux déterminés par corrélation d'images volumiques pour définir des conditions limites à appliquer sur les bords de sous-domaines dans l'échantillon pour les simulations. Les comparaisons directes de réseaux de microfissures 3D et de leur évolution montrent une très bonne capacité prédictive du modèle numériqueAn approach combining numerical simulations and experimental techniques is developed to model complex microcracking in heterogeneous cementitious materials. The proposed numerical model allowed us to predict accurately in 3D the initiation and the propagation of microcracks at the scale of the actual microstructure of a real sample subjected to compression. Its predictions have been validated by a direct comparison with the actual crack network characterized by 3D imaging techniques. In a first part, the numerical simulation tools are developed and tested. More specifically, the phase-field method is applied to microcracking simulations in highly heterogeneous microstructures and its advantages for such simulations are discussed. Then, the technique is extended to account for interfacial cracking, possibly occurring at inclusion/matrix interfaces. In a second part, the experimental methods used and developed in this work are described. The procedures to obtain the evolution of the 3D crack network within the samples by means of X-rays computed microtomography and in-situ mechanical testing are presented. Then, we focus on the developed image processing tools based on digital volume correlation to extract with good accuracy the cracks from the grey level images. In a third part, we compare the predictions of the numerical model with experimental results obtained, first, with a model material made of expanded polystyrene beads embedded in a plaster matrix, and second, to a more complex lightweight concrete. More precisely, we use the experimental data to identify by inverse approaches the local microstructural parameters, and use the experimental displacements measured by digital volume correlation to define boundary conditions to be applied on sub-domains within the sample for the simulations. The obtained direct comparisons of 3D microcrack networks and their evolutions demonstrate the very good predictive capability of the numerical model