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Fundamental Studies Of Strengthening Mechanisms In Metals Using Dislocation Dynamics
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Book Synopsis Fundamental Studies of Strengthening Mechanisms in Metals Using Dislocation Dynamics by :
Download or read book Fundamental Studies of Strengthening Mechanisms in Metals Using Dislocation Dynamics written by and published by . This book was released on 2006 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: A distributed dislocation method has been developed to quantify the elastic fields of inclusion eigenstrain problems in 2D and 3D (Lerma et al. 2003). The inclusions can be of any shape or size and the eigertstrains can be arbitrarily assigned, i.e. constant or non-constant within the inclusion. The method works well for material or field points inside or outside the inclusion domain, and is straightforward to apply. The method is based on discretizing the inclusion-matrix interface into a mesh of small regions of misfit represented in the method by dislocation loops with appropriately assigned Burgers vectors. The method works well for relatively far points from the inclusion although it also works for relatively close points at the expense of increasing the mesh density, i.e. the computational time involved. It was shown that, with increasing mesh density, the method converges into known analytical solutions for some specialized geometry and misfits. Recently, we have developed a new distributed-dislocation method for modeling eigenstrain problems such as gamma prime inclusions/particles in nickel-base superalloys. Here the dislocation loops representing the misfit are distributed throughout the volume of the inclusion with the dislocation lines themselves lying on the inclusion-matrix interface.
Book Synopsis Dislocation Dynamics and Plasticity by : Taira Suzuki
Download or read book Dislocation Dynamics and Plasticity written by Taira Suzuki and published by Springer Science & Business Media. This book was released on 2013-03-07 with total page 237 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the 1950s the direct observation of dislocations became possible, stimulat ing the interest of many research workers in the dynamics of dislocations. This led to major contributions to the understanding of the plasticity of various crys talline materials. During this time the study of metals and alloys of fcc and hcp structures developed remarkably. In particular, the discovery of the so-called in ertial effect caused by the electron and phonon frictional forces greatly influenced the quantitative understanding of the strength of these metallic materials. Statis tical studies of dislocations moving through random arrays of point obstacles played an important role in the above advances. These topics are described in Chaps. 2-4. Metals and alloys with bcc structure have large Peierls forces compared to those with fcc structure. The reasons for the delay in studying substances with bcc structure were mostly difficulties connected with the purification techniques and with microscopic studies of the dislocation core. In the 1970s, these difficulties were largely overcome by developments in experimental techniques and computer physics. Studies of dislocations in ionic and covalent bonding materials with large Peierls forces provided infonnation about the core structures of dislocations and their electronic interactions with charged particles. These are the main subjects in Chaps. 5-7.
Book Synopsis Dislocation Dynamics of Face-centered Cubic Metals and Alloys by : Ryan B. Sills
Download or read book Dislocation Dynamics of Face-centered Cubic Metals and Alloys written by Ryan B. Sills and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Face-centered cubic (FCC) metals and alloys--such as aluminum, copper, and austenitic stainless steel--are ubiquitous in the automotive, aerospace, and oil and gas industries. To further our understanding of the nature of plastic deformation in these materials, we have utilized dislocation dynamics (DD) simulations. We begin with a study of time integration in dislocation dynamics, examining the time-step-limiting aspects of DD, and developing a new subcycling-based time integrator that improves efficiency 100-fold. We then utilize this time integrator to study the basics of plasticity in pure, single crystalline copper. DD simulations were run over a wide range of strain rates and initial dislocation densities, examining how the yield strength and hardening rate vary, and making comparisons against the available experimental data. A detailed study on the contribution of binary dislocation junctions to hardening is then presented, showing that these junctions are an essential ingredient for hardening to occur. We then go on to study the most common strengthening mechanisms employed in FCC metals: solid solution strengthening and precipitation strengthening. After deriving the suitable chemical potential for the solute atoms comprising a solid solution, the influence of an "atmosphere" of solutes surrounding a dislocation on the stress field and line tension of the dislocation are examined, showing that these effects are generally small. The drag force exerted on dislocations by their atmospheres is then studied. We find these drag forces are often larger than those due to lattice friction, and can influence plasticity in FCC materials significantly. To study precipitation strengthening, a new algorithm for simulating dislocation-precipitate interactions is developed, which allows for ellipsoidal inclusions with arbitrary aspect ratio and arbitrary misfit. The new formulation is used to study Orowan looping in overaged aluminum-copper alloys, which have plate-like precipitates. The results and methods presented here constitute a broad set of advancements towards a more sound understanding of plastic deformation in FCC metals and alloys.
Book Synopsis The Plasticity of Metals at the Sub-micrometer Scale and Dislocation Dynamics in a Thin Film by : Seok Woo Lee
Download or read book The Plasticity of Metals at the Sub-micrometer Scale and Dislocation Dynamics in a Thin Film written by Seok Woo Lee and published by Stanford University. This book was released on 2011 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanotechnology has played a significant role in the development of useful engineering devices and in the synthesis of new classes of materials. For the reliable design of devices and for structural applications of materials with micro- or nano-sized features, nanotechnology has always called for an understanding of the mechanical properties of materials at small length scales. Thus, it becomes important to develop new experimental techniques to allow reliable mechanical testing at small scales. At the same time, the development of computational techniques is necessary to interpret the experimentally observed phenomena. Currently, microcompression testing of micropillars, which are fabricated by focused-ion beam (FIB) milling, is one of the most popular experimental methods for measuring the mechanical properties at the micrometer scale. Also, dislocation dynamics codes have been extensively developed to study the local evolution of dislocation structures. Therefore, we conducted both experimental and theoretical studies that shed new light on the factors that control the strength and plasticity of crystalline materials at the sub-micrometer scale. In the experimental work, we produced gold nanopillars by focused-ion beam milling, and conducted microcompression tests to obtain the stress-strain curves. Firstly, the size effects on the strength of gold nanopillars were studied, and "Smaller is Stronger" was observed. Secondly, we tried to change the dislocation densities to control the strength of gold nanopillars by prestraining and annealing. The results showed that prestraining dramatically reduces the flow strength of nanopillars while annealing restores the strength to the pristine levels. Transmission electron microscopy (TEM) revealed that the high dislocation density (~1015 m-2) of prestrained nanopillars significantly decreased after heavy plastic deformation. In order to interpret this TEM observation, potential dislocation source structures were geometrically analyzed. We found that the insertion of jogged dislocations before relaxation or enabling cross-slip during plastic flow are prerequisites for the formation of potentially strong natural pinning points and single arm dislocation sources. At the sub-micron scale, these conditions are most likely absent, and we argue that mobile dislocation starvation would occur naturally in the course of plastic flow. Two more outstanding issues have also been studied in this dissertation. The first involves the effects of FIB milling on the mechanical properties. Since micropillars are made by FIB milling, the damage layer at the free surface is always formed and would be expected to affect the mechanical properties at a sub-micron scale. Thus, pristine gold microparticles were produced by a solid-state dewetting technique, and the effects of FIB milling on both pristine and prestrained microparticles were examined via microcompression testing. These experiments revealed that FIB milling significantly reduces the strength of pristine microparticles, but does not alter that of prestrained microparticles. Thus, we confirmed that if there are pre-existing mobile-dislocations present in the crystal, FIB milling does not affect the mechanical properties. The second issue is the scaling law commonly used to describe the strength of micropillars as a function of sample size. For the scaling law, the power-law approximation has been widely used without understanding fundamental physics in it. Thus, we tried to analyze the power-law approximation in a quantitative manner with the well-known single arm source model. Material parameters, such as the friction stress, the anisotropic shear modulus, the magnitude of Burgers vector and the dislocation density, were explored to understand their effects on the scaling behavior. Considering these effects allows one to rationalize the observed material-dependent power-law exponents quantitatively. In another part of the dissertation, a computational study of dislocation dynamics in a free-standing thin film is described. We improved the ParaDiS (Parallel Dislocation Simulator) code, which was originally developed at the Lawrence Livermore National Laboratory, to deal with the free surface of a free-standing thin film. The spectral method was implemented to calculate the image stress field in a thin film. The faster convergence in the image stress calculation were obtained by employing Yoffe's image stress, which removes the singularity of the traction at the intersecting point between a threading dislocation and free surface. Using this newly developed code, we studied the stability of dislocation junctions and jogs, which are the potential dislocation sources, in a free standing thin film of a face-centered-cubic metal and discussed the creation of a dislocation source in a thin film. In summary, we have performed both microcompression tests and dislocation dynamics simulations to understand the dislocation mechanisms at the sub-micron scale and the related mechanical properties of metals. We believe that these experimental and computational studies have contributed to the enhancement of our fundamental knowledge of the plasticity of metals at the sub-micron scale.
Book Synopsis Fundamental Aspects of Dislocation Interactions by : G. Kostorz
Download or read book Fundamental Aspects of Dislocation Interactions written by G. Kostorz and published by Elsevier. This book was released on 2013-09-03 with total page 471 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamental Aspects of Dislocation Interactions: Low-Energy Dislocation Structures III covers the papers presented at a European Research Conference on Plasticity of Materials-Fundamental Aspects of Dislocation Interactions: Low-Energy Dislocation Structures III, held on August 30-September 4, 1992 in Ascona, Switzerland. The book focuses on the processes, technologies, reactions, transformations, and approaches involved in dislocation interactions. The selection first offers information on work softening and Hall-Petch hardening in extruded mechanically alloyed alloys and dynamic origin of dislocation structures in deformed solids. Discussions focus on stress-strain behavior in relation to composition, structure, and annealing; comparison of stress-strain curves with work softening theory; sweeping and trapping mechanism; and model of dipolar wall structure formation. The text then ponders on plastic instabilities and their relation to fracture and dislocation and kink dynamics in f.c.c. metals studied by mechanical spectroscopy. The book takes a look at misfit dislocation generation mechanisms in heterostructures and evolution of dislocation structure on the interfaces associated with diffusionless phase transitions. Discussions focus on dislocation representation of a wall of elastic domains; equation of equilibrium of an elastic domain; transformation of dislocations; and theoretical and experimental background. The selection is a valuable reference for readers interested in dislocation interactions.
Download or read book Scientific Bulletin written by and published by . This book was released on 1976 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Strengthening Mechanisms in Crystal Plasticity by : Ali Argon
Download or read book Strengthening Mechanisms in Crystal Plasticity written by Ali Argon and published by Oxford University Press on Demand. This book was released on 2008 with total page 425 pages. Available in PDF, EPUB and Kindle. Book excerpt: Technologically important metals and alloys have been strengthened throughout history by empirical means. The scientific bases of the central mechanisms of such forms of strengthening, developed over the past several decades are presented here through mechanistic models and associated experimental results.
Book Synopsis The Plasticity of Metals at the Sub-micrometer Scale and Dislocation Dynamics in a Thin Film by : Seok Woo Lee
Download or read book The Plasticity of Metals at the Sub-micrometer Scale and Dislocation Dynamics in a Thin Film written by Seok Woo Lee and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanotechnology has played a significant role in the development of useful engineering devices and in the synthesis of new classes of materials. For the reliable design of devices and for structural applications of materials with micro- or nano-sized features, nanotechnology has always called for an understanding of the mechanical properties of materials at small length scales. Thus, it becomes important to develop new experimental techniques to allow reliable mechanical testing at small scales. At the same time, the development of computational techniques is necessary to interpret the experimentally observed phenomena. Currently, microcompression testing of micropillars, which are fabricated by focused-ion beam (FIB) milling, is one of the most popular experimental methods for measuring the mechanical properties at the micrometer scale. Also, dislocation dynamics codes have been extensively developed to study the local evolution of dislocation structures. Therefore, we conducted both experimental and theoretical studies that shed new light on the factors that control the strength and plasticity of crystalline materials at the sub-micrometer scale. In the experimental work, we produced gold nanopillars by focused-ion beam milling, and conducted microcompression tests to obtain the stress-strain curves. Firstly, the size effects on the strength of gold nanopillars were studied, and "Smaller is Stronger" was observed. Secondly, we tried to change the dislocation densities to control the strength of gold nanopillars by prestraining and annealing. The results showed that prestraining dramatically reduces the flow strength of nanopillars while annealing restores the strength to the pristine levels. Transmission electron microscopy (TEM) revealed that the high dislocation density (~1015 m-2) of prestrained nanopillars significantly decreased after heavy plastic deformation. In order to interpret this TEM observation, potential dislocation source structures were geometrically analyzed. We found that the insertion of jogged dislocations before relaxation or enabling cross-slip during plastic flow are prerequisites for the formation of potentially strong natural pinning points and single arm dislocation sources. At the sub-micron scale, these conditions are most likely absent, and we argue that mobile dislocation starvation would occur naturally in the course of plastic flow. Two more outstanding issues have also been studied in this dissertation. The first involves the effects of FIB milling on the mechanical properties. Since micropillars are made by FIB milling, the damage layer at the free surface is always formed and would be expected to affect the mechanical properties at a sub-micron scale. Thus, pristine gold microparticles were produced by a solid-state dewetting technique, and the effects of FIB milling on both pristine and prestrained microparticles were examined via microcompression testing. These experiments revealed that FIB milling significantly reduces the strength of pristine microparticles, but does not alter that of prestrained microparticles. Thus, we confirmed that if there are pre-existing mobile-dislocations present in the crystal, FIB milling does not affect the mechanical properties. The second issue is the scaling law commonly used to describe the strength of micropillars as a function of sample size. For the scaling law, the power-law approximation has been widely used without understanding fundamental physics in it. Thus, we tried to analyze the power-law approximation in a quantitative manner with the well-known single arm source model. Material parameters, such as the friction stress, the anisotropic shear modulus, the magnitude of Burgers vector and the dislocation density, were explored to understand their effects on the scaling behavior. Considering these effects allows one to rationalize the observed material-dependent power-law exponents quantitatively. In another part of the dissertation, a computational study of dislocation dynamics in a free-standing thin film is described. We improved the ParaDiS (Parallel Dislocation Simulator) code, which was originally developed at the Lawrence Livermore National Laboratory, to deal with the free surface of a free-standing thin film. The spectral method was implemented to calculate the image stress field in a thin film. The faster convergence in the image stress calculation were obtained by employing Yoffe's image stress, which removes the singularity of the traction at the intersecting point between a threading dislocation and free surface. Using this newly developed code, we studied the stability of dislocation junctions and jogs, which are the potential dislocation sources, in a free standing thin film of a face-centered-cubic metal and discussed the creation of a dislocation source in a thin film. In summary, we have performed both microcompression tests and dislocation dynamics simulations to understand the dislocation mechanisms at the sub-micron scale and the related mechanical properties of metals. We believe that these experimental and computational studies have contributed to the enhancement of our fundamental knowledge of the plasticity of metals at the sub-micron scale.
Book Synopsis Strengthening Methods in Crystals by : Sir Robin Nicholson
Download or read book Strengthening Methods in Crystals written by Sir Robin Nicholson and published by Halsted Press. This book was released on 1972 with total page 648 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fundamentals of Creep in Metals and Alloys by : Michael E. Kassner
Download or read book Fundamentals of Creep in Metals and Alloys written by Michael E. Kassner and published by Elsevier. This book was released on 2004-04-06 with total page 289 pages. Available in PDF, EPUB and Kindle. Book excerpt: * Numerous line drawings with consistent format and units allow easy comparison of the behavior of a very wide range of materials * Transmission electron micrographs provide a direct insight in the basic microstructure of metals deforming at high temperatures * Extensive literature review of over 1000 references provide an excellent reference document, and a very balanced discussion Understanding the strength of materials at a range of temperatures is critically important to a huge number of researchers and practitioners from a wide range of fields and industry sectors including metallurgists, industrial designers, aerospace R&D personnel, and structural engineers. The most up-to date and comprehensive book in the field, Fundamentals of Creep in Metals and Alloys discusses the fundamentals of time-dependent plasticity or creep plasticity in metals, alloys and metallic compounds. This is the first book of its kind that provides broad coverage of a range of materials not just a sub-group such as metallic compounds, superalloys or crystals. As such it presents the most balanced view of creep for all materials scientists. The theory of all of these phenomena are extensively reviewed and analysed in view of an extensive bibliography that includes the most recent publications in the field. All sections of the book have undergone extensive peer review and therefore the reader can be sure they have access to the most up-to-date research, fully interrogated, from the world’s leading investigators. · Numerous line drawings with consistent format and units allow easy comparison of the behavior of a very wide range of materials· Transmission electron micrographs provide a direct insight in the basic microstructure of metals deforming at high temperatures· Extensive literature review of over 1000 references provide an excellent reference document, and a very balanced discussion
Book Synopsis TMS 2019 148th Annual Meeting & Exhibition Supplemental Proceedings by : & The Minerals, Metals Materials Society
Download or read book TMS 2019 148th Annual Meeting & Exhibition Supplemental Proceedings written by & The Minerals, Metals Materials Society and published by Springer. This book was released on 2019-02-26 with total page 1731 pages. Available in PDF, EPUB and Kindle. Book excerpt: This collection features papers presented at the 148th Annual Meeting & Exhibition of The Minerals, Metals & Materials Society.
Book Synopsis Fundamental Aspects of Dislocation Theory by : John Arthur Simmons
Download or read book Fundamental Aspects of Dislocation Theory written by John Arthur Simmons and published by . This book was released on 1970 with total page 752 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Metal Matrix Composites by : Minoru Taya
Download or read book Metal Matrix Composites written by Minoru Taya and published by Elsevier. This book was released on 2016-01-11 with total page 275 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal Matrix Composites: Thermomechanical Behavior discusses metal matrix composites, elaborating on that consists of two phases—fiber as reinforcement and metal as matrix. This book focuses on polymer matrix composites, including topics in metal matrix composites ranging from processing to fracture mechanics. The three basic types of composite materials—dispersion-strengthened, particle-reinforced, and fiber (whisker)-reinforced, are also described in detail. Dispersion-strengthened is characterized by a microstructure consisting of an elemental matrix within which fine particles are uniformly dispersed, while particle-reinforced is indicated by dispersed particles of greater than 1.0 μm diameter with a volume fraction of 5 to 40%. Fiber (whisker)-reinforced provides a distinguishing microstructural feature of fiber-reinforced materials, such as that the reinforcing fiber has one long dimension, while the reinforcing particles of the other two types do not. This publication serves as a reference data book to students and researchers aiming to acquire knowledge of the thermomechanical behavior of metal matrix composites.
Book Synopsis Fundamentals of Strength by : Paul Follansbee
Download or read book Fundamentals of Strength written by Paul Follansbee and published by Springer Nature. This book was released on 2022-07-28 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt: This second edition updates and expands on the class-tested first edition text, augmenting discussion of dynamic strain aging and austenitic stainless steels and adding a section on analysis of nickel-base superalloys that shows how the mechanical threshold stress (MTS) model, an internal state variable constitutive formulation, can be used to de-convolute synergistic effects. The new edition retains a clear and rigorous presentation of the theory, mechanistic basis, and application of the MTS model. Students are introduced to critical competencies such as crystal structure, dislocations, thermodynamics of slip, dislocation–obstacle interactions, deformation kinetics, and hardening through dislocation accumulation. The model described in this volume facilitates readers’ understanding of integrated computational materials engineering (ICME), presenting context for the transition between length scales characterizing the mesoscale (mechanistic) and the macroscopic. Presenting readers a model buttressed by detailed examples and applications, the textbook is ideal for students, practitioners, and materials researchers.
Download or read book Research in Progress written by and published by . This book was released on 1969 with total page 746 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Effects of Grain Boundary Structure in Discrete Simulations of Multiscale Dislocation Dynamics by : Nathaniel Burbery
Download or read book Effects of Grain Boundary Structure in Discrete Simulations of Multiscale Dislocation Dynamics written by Nathaniel Burbery and published by . This book was released on 2017 with total page 251 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research develops a multiscale approach to study the defect-driven evolution of the microstructure in polycrystalline FCC metals, by using atomic-informed models to reproduce multi-grain, microscale simulations with discrete dislocation dynamics (DD). The dynamically evolving dislocation and grain boundary (GB) microstructure dictate the non-linear ‘plastic’ response of polycrystalline metals during deformation. The processes of intercrystalline plastic coupling are generally a consequence of multi-dislocation pile up interactions with GBs, however such effects are beyond feasible limits of conventional atomic simulations or experimental studies. More accurate computational models of the discrete micro-macro scale dislocation and GB dynamics could be applied to elucidate the fundamental mechanisms and reduce the dependence on costly experimental testing. This work expands upon the physics-based single crystal DD framework by using molecular dynamics simulations to develop structure-property models that compensate for the variable characteristics of GB interfaces. This research involved studies with a broad set of equilibrium, non-equilibrium and metastable atomic bicrystals. The results showed that the intercrystalline strength was strongly influenced by the ‘GB shape’ characteristics of the structural free volume, in addition to the intrinsic energy. Defect interaction studies verified the realistic conditions for the observation of structural multiplicity, and showed the significance of intermediate ‘transitory’ GB states. Observation of the slip transmission process showed that the GB dislocations acted as pinning sites, so that the intercrystalline plasticity resembled Orowan-type obstacle bypassing. A novel multi-orientation approach was developed to provide a control routine for modelling atomistic dislocation dynamics that enabled a self-consistent multiscale comparison with DD simulations. Insights regarding dislocation core construction and Burgers vector analysis played an integral role in the development of atomically accurate DD representations of the GB dislocation structures. A world-first 3D polycrystal DD approach was implemented to provide a discrete representation of the dislocation structure of high angle GBs, through the culmination of the atomistic insights and many years of concerted code development. This robust, versatile implementation enables tailor-made polycrystal simulation specimens with arbitrary shape, grain orientation and size to be generated from common .stl files. The unique, comprehensive modelling framework provides a realistic reproduction of key intercrystalline slip mechanisms including GB sliding, dissociation and absorption, dislocation transmission and reflection. As such, the present work provides a novel contribution of relevance, particularly, to the developing sector of GB engineered nanocrystalline materials.
Book Synopsis Crystal Plasticity Finite Element Methods by : Franz Roters
Download or read book Crystal Plasticity Finite Element Methods written by Franz Roters and published by John Wiley & Sons. This book was released on 2011-08-04 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.
