Download or read book Plasticity and Failure in Nanocrystalline BCC Metals Via Molecular Dynamics Simulation written by and published by . This book was released on 2010 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in the ability to generate extremely high pressures in dynamic experiments such as at the National Ignition Facility has motivated the need for special materials optimized for those conditions as well as ways to probe the response of these materials as they are deformed. We need to develop a much deeper understanding of the behavior of materials subjected to high pressure, especially the effect of rate at the extremely high rates encountered in those experiments. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum at pressures less than 100 GPa to investigate the processes associated with plastic deformation for strains up to 100%. We focus on 3D polycrystalline systems with typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures. We also present some results on void growth in nanocrystalline BCC metals under tension.

Download or read book Plasticity and Failure in Nanocrystalline BCC Metals Via MD Simulation written by and published by . This book was released on 2010 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in the ability to generate extremely high pressures in dynamic experiments such as at the National Ignition Facility has motivated the need for special materials optimized for those conditions as well as ways to probe the response of these materials as they are deformed. We need to develop a much deeper understanding of the behavior of materials subjected to high pressure, especially the effect of rate at the extremely high rates encountered in those experiments. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum at pressures less than 100 GPa to investigate the processes associated with plastic deformation for strains up to 100%. We focus on 3D polycrystalline systems with typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures. We also present some results on void growth in nanocrystalline BCC metals under tension.

Download or read book Characterization of Nanocomposites written by Frank Abdi and published by CRC Press. This book was released on 2017-03-31 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: These days, advanced multiscale hybrid materials are being produced in the industry, studied by universities, and used in several applications. Unlike for macromaterials, it is difficult to obtain the physical, mechanical, electrical, and thermal properties of nanomaterials because of the scale. Designers, however, must have knowledge of these properties to perform any finite element analysis or durability and damage tolerance analysis. This is the book that brings this knowledge within easy reach. What makes the book unique is the fact that its approach that combines multiscale multiphysics and statistical analysis with multiscale progressive failure analysis. The combination gives a very powerful tool for minimizing tests, improving accuracy, and understanding the effect of the statistical nature of materials, in addition to the mechanics of advanced multiscale materials, all the way to failure. The book focuses on obtaining valid mechanical properties of nanocomposite materials by accurate prediction and observed physical tests, as well as by evaluation of test anomalies of advanced multiscale nanocomposites containing nanoparticles of different shapes, such as chopped fiber, spherical, and platelet, in polymeric, ceramic, and metallic materials. The prediction capability covers delamination, fracture toughness, impact resistance, conductivity, and fire resistance of nanocomposites. The methodology employs a high-fidelity procedure backed with comparison of predictions with test data for various types of static, fatigue, dynamic, and crack growth problems. Using the proposed approach, a good correlation between the simulation and experimental data is established.

Download or read book A Quantized Crystal Plasticity Model for Nanocrystalline Metals written by Lin Li and published by . This book was released on 2011 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Nanocrystalline (NC) metals, which consist of grains or crystallites with sizes less than 100 nm, have exhibited unique mechanical and physical properties, in comparison to coarse-grained (CG) counterparts. The appealing mechanical properties, for instance, include extremely high strengths, very extended elastic-plastic transitions, and unprecedented magnitudes of recoverable plastic strain. Further, footprints of inter-granular stresses measured from diffraction experiments are distinct for NC metals vs. CG metals. In particular, recent in-situ synchrotron measurements reveal that residual lattice strains change rather modestly even after imposing macro plastic strains to ~1%. Remarkably, over the same regime, the corresponding residual peak widths decrease. These phenomena are in sharp contrast to CG metals, for which residual lattice strain and peak widths both increase with deformation. In this dissertation, a quantized crystal plasticity (QCP) model is developed to explore the aforementioned unique NC features. The QCP model employs a crystallographic description of dislocation slip plasticity; in particular, single slip events across nano scale grains impart large (~1%) increments in grain-averaged plastic shear. Therefore, plasticity does not proceed in a smooth, continuous fashion but rather via strain jumps, imparting violent grain-to-grain redistribution in stress. This discrete feature is consistent with recent Molecular Dynamics (MD) simulations, which illustrate a dramatic jump in grain-averaged shear strain when a dislocation spontaneously transverses a nano grain interior after depinning from grain boundary (GB) ledges. Finite element simulations implementing this quantized plasticity approach predict the experimental properties of enhanced strength, extended elastic-plastic strain, and recoverable plastic strain, as well as the trends in residual lattice strain and peak width mentioned, but only under certain conditions. First, the grain-to-grain distribution of critical stress for slip activation is very different from that for CG materials. In particular, no events occur below a rather large threshold stress ~ 1/grain size; and above this threshold, a very asymmetric distribution predominates, signifying that a relatively large number of easier-to-slip grains are balanced by a minority of harder-to-slip grains. Second, there exists a large residual stress state, which can be removed via post deformation. The quantized crystal plasticity provides an alternate view of NC deformation, compared to hypotheses in the literature that are centered on GB sliding or deformation of a GB phase separated from grain interior. The QCP model is capable of bridging the disparity in length and time scales between MD simulations and physical experiments, and as well establishes an insightful connection between them.

Download or read book Multiscale modeling of contact plasticity and nanoindentation in nanostructured FCC metals written by Virginie Dupont and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT Nanocrystalline thin films are materials with a grain size less than 100 nm which are commonly used to fabricate microscale electro-mechanical devices. At such small scale, nanoindentation is the only standard experimental technique to study the mechanical properties of thin films. However, it is unclear if the continuum laws commonly used in nanoindentation analysis of polycrystalline materials are still valid for nano-grained metals. It is therefore critical to better understand the behavior of nanocrystalline materials under nanoscale contact. This dissertation summarizes the results of atomistic simulations aimed at modeling the nanoindentation of nanocrystalline metal thin films for which the grain size is smaller than the indenter diameter. The nanoindentation of aluminum thin films was first studied using the Quasicontinuum method, which is a concurrent multiscale model where regions of small gradients of deformations are represented as a continuum medium by finite elements, and regions of high gradients of deformation are fully-treated atomistically. Two embeddedatom- method potentials for aluminum were used in order to study the effect of the potential on the nanoindentation behavior. The aim is to better understand the effects of a grain boundary network on the plasticity and the underlying mechanisms from an atomistic perspective. Our results show that a grain boundary network is the primary medium of plasticity at the nanoscale, via shear banding that causes flow serration. We also show that although the dislocation mechanisms are the same, the mechanisms involving grain boundaries are different depending on the interatomic potential. In a second part, abnormal grain growth in aluminum thin films under nanoindentation is studied using both the Quasicontinuum method and parallel molecular dynamics simulations. The effects of the potential, the nature of the indenter and of its size on the grain growth under nanoindentation are investigated. Our results show that the potential used, which can be related to the purity of the material, can reduce grain growth. We also show that the size and material used for the indenter both have significant effects on grain growth. More specifically, grain growth under the indenter is found to occur via atom diffusion if the indenter is of the same material as the thin film. Finally, the sample size effects were studied using parallel molecular dynamics simulations on nickel thin films and nanowires. Single crystals with different sizes are modeled in order to investigate the effects of the free boundaries as well as of the thickness of the samples. It is shown that the yield point and the incipient plasticity mechanisms are similar for all simulations. However, the hardness of the nanowires is found to decrease with the nanowire size during nanoindentation, due to the interaction of prismatic loops and dislocations with the free boundaries. This dissertation has shed light on the plastic deformation mechanisms under nanoscale contact. The results obtained will help the scientific community gain a better understanding of the behavior of nanomaterials, which will lead to the fabrication of more reliable nanodevices.

Download or read book A Molecular Dynamics Study of Nanocontact Plasticity and Dislocation Avalanches in FCC and BCC Crystals written by Javier Varillas and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study aims to investigate the underlying mechanisms which govern the development of dense defect networks in nanoscale crystal plasticity, either under contact and uniaxial loading conditions, with emphasis on the onset of intermittent avalanche phenomena. The investigation is based on a comprehensive set of massive molecular dynamics (MD) simulations performed with embedded-atom method potentials in face-centered cubic (FCC) and body-centered cubic (BCC) crystals. The first part of the thesis concerns the combined role of elasticity and plasticity in nanocontact loadings, where attention is given to the mechanisms leading to the formation of a permanent nanoimprint as well as to the onset of material pile-up at the contact vicinity. It is found that the topographical arrangement of the slip traces emitted at the surface into specific deformation patterns is a distinctive feature of the underlying dislocation glide and twinning processes occurring in FCC and BCC crystals as a function of temperature and surface orientation. A mechanistic analysis is made on the influence of the defect nucleation events in conjunction with the development of entangled defect networks upon the material hardness and its evolution towards a plateau level with increasing indenter-tip penetration. Complementary MD simulations of the uniaxial stress-strain curve of the plastically deformed region are carried out with the purpose of establishing a direct correlation between nanoscale material responses attaining under uniaxial and contact loading conditions. The results of this comparison illustrate on the key role played by defect nucleation processes on the formation of permanent nanoimprints, which differs from the conventional view in that in micro and macroscopic scales imprint formation is essentially governed by the evolutionary character of a preexisting (entangled) defect network: the greater the dislocation density, the larger the measured hardness. In overall, this work provides a fundamental insight into the understanding of why BCC surfaces are harder than FCC surfaces at the nanoscale. A statistical physics background is devised to investigate the influence of the dislocation mechanisms on the onset of avalanche events that are inherent to crystal plasticity. The analysis is predicated upon the notion in that the size distribution of such avalanches follows power-law scaling. To investigate the avalanche size distributions in cubic crystals, a group of novel MD simulations are performed where the computational cells containing a periodic arrangement of a preexisting dislocation network are subjected to uniaxial straining under displacement control at different strain rates and temperatures. Under sufficiently slow driving, the dislocation networks evolve through the emission of dislocation avalanches which do not overlap in time. This illustrates that the mobilized entangled dislocation arrangements exhibit quiescent periods during each plastic (dissipative) event, enabling comparison with experimental results which are also performed under strict displacement controlled conditions. The results illustrate on the attainment of a transitional slip size separating two power-law avalanche regimes as a function of the fundamental dislocation glide processes at the crossroads of self-organized and tuned criticality models. Detailed analyses of the MD simulations furnish specific mechanisms characterizing dislocation avalanche emission and propagation in FCC and BCC metals throughout a wide temperature range, which is central in supporting the onset of the aforementioned two power-law regimes.

Download or read book Quantification of Grain Boundary Mediated Plasticity Mechanisms in Nanocrystalline Metals written by Jason F. Panzarino and published by . This book was released on 2016 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystalline metals have been a topic of great discussion over recent years due to their exceptional strengths and novel grain boundary-mediated deformation mechanisms. Their microstructures are known to evolve through dynamic processes such as grain boundary migration and grain rotation, but how the collective interaction of these mechanisms alter the microstructure on a larger scale is not completely understood. In this thesis, we present coupled atomistic modeling and experimental tasks that aim to understand how the grain structure, grain boundaries, and associated grain boundary network change during nanocrystalline plasticity. Due to the complex three-dimensional nature of these mechanisms and the limited spatial and temporal resolution of current in-situ experimental techniques, we turn to atomistic modeling to help understand the dynamics by which these mechanisms unfold. In order to provide a quantitative analysis of this behavior, we develop a tool which fully characterizes nanocrystalline microstructures in atomistic models and subsequently tracks their evolution during molecular dynamics simulations. We then use this algorithm to quantitatively track grain structure and boundary network evolution in plastically deformed nanocrystalline Al, finding that higher testing temperature and smaller average grain size results in increased evolution of grain structure with evidence of larger scale changes to the grain boundary network also taking place. This prompts us to extend our analysis technique to include full characterization of grain boundary networks and rigorous topographical feature identification. We then employ this tool on simulations of Al subject to monotonic tension, cycling loading, and simple annealing, and find that each case results in different evolution of the grain boundary network. Finally, our computational work is complemented synergistically by experimental analyses which track surface microstructure evolution during sliding wear of nanocrystalline Ni-W thin films. These experiments track the development of a surface grain growth layer which evolves through grain boundary mediated plasticity and we are able to make direct connections between this evolution and that which was observed in our simulation work. All of the findings of this thesis are a direct result of the dynamic and collective nature by which nanocrystalline materials deform.

Download or read book Molecular Dynamics Simulation of Dislocation Mobility of a Body centered Cubic Metal written by Jinpeng Chang and published by . This book was released on 2000 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Applied Nanoindentation in Advanced Materials written by Atul Tiwari and published by John Wiley & Sons. This book was released on 2017-10-30 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research in the area of nanoindentation has gained significant momentum in recent years, but there are very few books currently available which can educate researchers on the application aspects of this technique in various areas of materials science. Applied Nanoindentation in Advanced Materials addresses this need and is a comprehensive, self-contained reference covering applied aspects of nanoindentation in advanced materials. With contributions from leading researchers in the field, this book is divided into three parts. Part one covers innovations and analysis, and parts two and three examine the application and evaluation of soft and ceramic-like materials respectively. Key features: A one stop solution for scholars and researchers to learn applied aspects of nanoindentation Contains contributions from leading researchers in the field Includes the analysis of key properties that can be studied using the nanoindentation technique Covers recent innovations Includes worked examples Applied Nanoindentation in Advanced Materials is an ideal reference for researchers and practitioners working in the areas of nanotechnology and nanomechanics, and is also a useful source of information for graduate students in mechanical and materials engineering, and chemistry. This book also contains a wealth of information for scientists and engineers interested in mathematical modelling and simulations related to nanoindentation testing and analysis.

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.

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.

Download or read book Dynamic Behavior of Materials written by Marc A. Meyers and published by John Wiley & Sons. This book was released on 1994-10-28 with total page 694 pages. Available in PDF, EPUB and Kindle. Book excerpt: Addresses fundamentals and advanced topics relevant to the behavior of materials under in-service conditions such as impact, shock, stress and high-strain rate deformations. Deals extensively with materials from a microstructure perspective which is the future direction of research today.

Download or read book Metals Abstracts written by and published by . This book was released on 1999 with total page 1014 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nanostructured Metals and Alloys written by S H Whang and published by Elsevier. This book was released on 2011-03-22 with total page 840 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tensile strength, fatigue strength and ductility are important properties of nanostructured metallic materials, which make them suitable for use in applications where strength or strength-to-weight ratios are important. Nanostructured metals and alloys reviews the latest technologies used for production of these materials, as well as recent advances in research into their structure and mechanical properties.One of the most important issues facing nanostructured metals and alloys is how to produce them. Part one describes the different methods used to process bulk nanostructured metals and alloys, including chapters on severe plastic deformation, mechanical alloying and electrodeposition among others. Part two concentrates on the microstructure and properties of nanostructured metals, with chapters studying deformation structures such as twins, microstructure of ferrous alloys by equal channel angular processing, and characteristic structures of nanostructured metals prepared by plastic deformation. In part three, the mechanical properties of nanostructured metals and alloys are discussed, with chapters on such topics as strengthening mechanisms, nanostructured metals based on molecular dynamics computer simulations, and surface deformation. Part four focuses on existing and developing applications of nanostructured metals and alloys, covering topics such as nanostructured steel for automotives, steel sheet and nanostructured coatings by spraying.With its distinguished editor and international team of contributors, Nanostructured metals and alloys is a standard reference for manufacturers of metal components, as well as those with an academic research interest in metals and materials with enhanced properties.

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.

Download or read book Magnesium Alloys and Technologies written by Karl U. Kainer and published by John Wiley & Sons. This book was released on 2006-03-06 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: The need for light-weight materials, especially in the automobile industry, created renewed interest in innovative applications of magnesium materials. This demand has resulted in increased research and development activity in companies and research institutes in order to achieve an improved property profile and better choice of alloy systems. Here, development trends and application potential in different fields like the automotive industry and communication technology are discussed in an interdisciplinary framework.

Download or read book Diffusion in Solids written by Helmut Mehrer and published by Springer Science & Business Media. This book was released on 2007-07-24 with total page 645 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book describes the central aspects of diffusion in solids, and goes on to provide easy access to important information about diffusion in metals, alloys, semiconductors, ion-conducting materials, glasses and nanomaterials. Coverage includes diffusion-controlled phenomena including ionic conduction, grain-boundary and dislocation pipe diffusion. This book will benefit graduate students in such disciplines as solid-state physics, physical metallurgy, materials science, and geophysics, as well as scientists in academic and industrial research laboratories.