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Author: Prita Pant
Publisher:
ISBN:
Category : Deformations (Mechanics)
Languages : en
Pages : 410
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Book Description
Author: Prita Pant
Publisher:
ISBN:
Category : Deformations (Mechanics)
Languages : en
Pages : 410
Get Book Here
Book Description
Author: Oliver Kraft
Publisher:
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 250
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Book Description
The mechanical properties of small volumes of materials (such as thin films and patterned structures) can be very different from larger volumes, especially in the area of dislocation behavior. This text contains a selection of 31 papers from the April 2001 symposium devoted to new methods of dislocation modeling. Topics include mechanisms of plastic deformation in heteroepitaxial, multilayered, and polycrystalline thin films; as well as in 3D mesostructures such as epitaxial islands, semiconducting devices, and microcrystallites. The organizers of the symposium had the particular aim of stimulating exchange between experimental work, theoretical modeling, and numerical simulations. Annotation copyrighted by Book News Inc., Portland, OR.
Author: G. Kostorz
Publisher: Elsevier
ISBN: 1483274926
Category : Technology & Engineering
Languages : en
Pages : 471
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Book Description
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.
Author: Ray Stuart Fertig
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Single-crystal films were simulated using three-dimensional discrete dislocation dynamics simulations, where an initial distribution of dislocation loops was allowed to move naturally in response to successive applied strains. The types of interactions that stopped threading dislocations (threads) were identified and the relative fraction of threads stopped in each interaction was determined. An inhomogeneous stress field in the film evolved as the dislocation structure evolved. Threads were observed to interact primarily in regions of low stress. The simulations were used as a virtual test bed for understanding dislocation behavior in thin films. The intuition gained from the simulations led to the construction of three models, which are discussed in detail. First, a model was developed to determine the capture cross-section of a thread, such that if another thread was within its capture cross-section the two threads would interact. Second, a statistical model was constructed to evaluate the effect of stress inhomogeneity on the local concentration of threads. Finally, results from the simulations and analytical models were used to construct a model of strain hardening in thin films based on fundamental behavior of dislocations in thin films.
Author: Seok Woo Lee
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 186
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Book Description
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.
Author: Oliver Kraft
Publisher: Cambridge University Press
ISBN: 9781107412163
Category : Technology & Engineering
Languages : en
Pages : 238
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Book Description
The mechanical properties of small volumes of materials such as thin films and patterned structures can be very different from the mechanical properties of those same materials in bulk. Many explanations of the mechanical behaviors of such small volumes have depended on simplified models of dislocation behavior. However, recent developments in dislocation modeling have made it possible to understand dislocation behavior in much more detail than before. A wide range of topics is presented in these proceedings, including mechanisms of plastic deformation in heteroepitaxial, multilayered and polycrystalline thin films, as well as three-dimensional mesostructures such as epitaxial islands, semiconducting devices and microcrystallites. Experimental, theoretical and numerical simulations are addressed. Topics include: dislocation and deformation mechanisms in thin metal films and multilayers; discrete dislocations - observations and simulations; dislocations and deformation mechanisms in thin films and small structures; dislocations in small structures; dislocations and deformation in epitaxial layers; dislocation fundamentals -observations, calculations and simulations.
Author: L. B. Freund
Publisher: Cambridge University Press
ISBN: 9781139449823
Category : Technology & Engineering
Languages : en
Pages : 772
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Book Description
Thin film mechanical behavior and stress presents a technological challenge for materials scientists, physicists and engineers. This book provides a comprehensive coverage of the major issues and topics dealing with stress, defect formation, surface evolution and allied effects in thin film materials. Physical phenomena are examined from the continuum down to the sub-microscopic length scales, with the connections between the structure of the material and its behavior described. Theoretical concepts are underpinned by discussions on experimental methodology and observations. Fundamental scientific concepts are embedded through sample calculations, a broad range of case studies with practical applications, thorough referencing, and end of chapter problems. With solutions to problems available on-line, this book will be essential for graduate courses on thin films and the classic reference for researchers in the field.
Author: Christopher Robert Weinberger
Publisher:
ISBN:
Category :
Languages : en
Pages : 352
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Book Description
Author: L. Kubin
Publisher: Oxford University Press (UK)
ISBN: 019852501X
Category : Science
Languages : en
Pages : 320
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Book Description
In the past twenty years, new experimental approaches, improved models and progress in simulation techniques brought new insights into long-standing issues concerning dislocation-based plasticity in crystalline materials. Dislocation dynamics simulations are becoming accessible to a wide range of users. This book presents to students and researchers in materials science and mechanical engineering a comprehensive coverage of the physical body of knowledge on whichthey are based. This includes classical studies, which are too often ignored, recent experimental and theoretical advances, as well as a discussion of selected applications on various topics.
Author: Peter M. Anderson
Publisher: Cambridge University Press
ISBN: 1316785106
Category : Technology & Engineering
Languages : en
Pages : 721
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Book Description
Theory of Dislocations provides unparalleled coverage of the fundamentals of dislocation theory, with applications to specific metal and ionic crystals. Rather than citing final results, step-by-step developments are provided to offer an in-depth understanding of the topic. The text provides the solid theoretical foundation for researchers to develop modeling and computational approaches to discrete dislocation plasticity, yet it covers important experimental observations related to the effects of crystal structure, temperature, nucleation mechanisms, and specific systems. This new edition incorporates significant advances in theory, experimental observations of dislocations, and new findings from first principles and atomistic treatments of dislocations. Also included are new discussions on thin films, deformation in nanostructured systems, and connection to crystal plasticity and strain gradient continuum formulations. Several new computer programs and worked problems allow the reader to understand, visualize, and implement dislocation theory concepts.
