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Author: Kristopher Learion Baker
Publisher:
ISBN:
Category :
Languages : en
Pages : 150
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Book Description
Atomistic simulations can illuminate detailed mechanisms of brittle and ductile fracture and plasticity. However, there are many limitations to these simulations like short timescales, small spatial scales, and limitations of the discretization. Using molecular dynamics (MD) and multiscale methods, adaptations can be made to allow MD to answer problems relevant to engineers. In the first of three examples, MD is adapted to simulate brittle fracture by changing the discretization and allowing permanent damage between particles. By changing the discretization, specific mechanisms inherent to MD can be suppressed to allow accurate, macroscopic simulations of dynamic fragmentation of brittle materials. Second, the timescale available to MD is extended in a concurrent multiscale method (CADD) combined with accelerated MD. This combined approach allows for microseconds of simulation time at experimentally achievable loading rates. The method is applied to crack opening in aluminum alloys, and the effect of the loading rate on crack growth mechanisms is observed. From the results, it is clear that crack growth mechanisms depend greatly on the rate of the far-field loading. Third, the effect of aging on fatigue crack growth is studied by varying the resistance to dislocation motion in the dislocation dynamics region of CADD. Only in a multiscale simulation like CADD, can dislocation pileups reaching microns into the material interact with the atomic-scale mechanisms at a crack tip. The results of the simulations indicated that increasing the friction force raises the fatigue crack threshold. Also, a transition from stage I fatigue crack growth to stage II fatigue crack growth occurs by dislocations shielding dislocation nucleation on the primary slip plane. These observations support the conclusion that the fatigue crack growth threshold is controlled by the spacing between obstacles to dislocation glide, which is consistent with experimental observations.
Author: Kristopher Learion Baker
Publisher:
ISBN:
Category :
Languages : en
Pages : 150
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Book Description
Atomistic simulations can illuminate detailed mechanisms of brittle and ductile fracture and plasticity. However, there are many limitations to these simulations like short timescales, small spatial scales, and limitations of the discretization. Using molecular dynamics (MD) and multiscale methods, adaptations can be made to allow MD to answer problems relevant to engineers. In the first of three examples, MD is adapted to simulate brittle fracture by changing the discretization and allowing permanent damage between particles. By changing the discretization, specific mechanisms inherent to MD can be suppressed to allow accurate, macroscopic simulations of dynamic fragmentation of brittle materials. Second, the timescale available to MD is extended in a concurrent multiscale method (CADD) combined with accelerated MD. This combined approach allows for microseconds of simulation time at experimentally achievable loading rates. The method is applied to crack opening in aluminum alloys, and the effect of the loading rate on crack growth mechanisms is observed. From the results, it is clear that crack growth mechanisms depend greatly on the rate of the far-field loading. Third, the effect of aging on fatigue crack growth is studied by varying the resistance to dislocation motion in the dislocation dynamics region of CADD. Only in a multiscale simulation like CADD, can dislocation pileups reaching microns into the material interact with the atomic-scale mechanisms at a crack tip. The results of the simulations indicated that increasing the friction force raises the fatigue crack threshold. Also, a transition from stage I fatigue crack growth to stage II fatigue crack growth occurs by dislocations shielding dislocation nucleation on the primary slip plane. These observations support the conclusion that the fatigue crack growth threshold is controlled by the spacing between obstacles to dislocation glide, which is consistent with experimental observations.
Author: Sixie Huang
Publisher:
ISBN:
Category :
Languages : en
Pages : 96
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Book Description
"The mechanical behavior of Metallic Nanolayered Composites (MNCs) is governed by their underlying microstructure. In this dissertation, the roles of the interlayer spacing (grain size, d) and the intralayer biphase spacing (layer thickness, h) on mechanical response of Cu/Nb MNCs are examined by Molecular Dynamics (MD) simulations. The study of the strength of MNCs show that small changes in both d and h play a profound role in the relative plastic contributions from grain boundary sliding and dislocation glide. The interplay of d and h leads to a very broad transition region from grain boundary sliding dominated flow, where the strength of the material is weak and insensitive to changes in h, to grain boundary dislocation emission and glide dominated flow, where the strength of the material is strong and sensitive to changes in h. The study of the fracture behavior of MNCs shows that cracks in Cu and Nb layers may exhibit different propagation paths and distances under the same external loading. Interfaces can improve the fracture resistance of the Nb layer in Cu/Nb MNCs by providing mobile dislocation sources to generate the plastic strain at the crack tip necessary for crack blunting. Increasing the layer thickness can further enhance the fracture resistance of both Cu and Nb layers, since the critical stress for activating dislocation motion decreases with increasing the layer thickness. A novel atomistic-informed interface-dislocation dynamics (I-DD) model has been developed to study Metal-Ceramic Nanolayered Composites (MCNCs) based on the key deformation process and microstructure features revealed by MD simulations. The I-DD predicted results match well with the prior experimental results where both yield stress and strain hardening rate increase as the layer thickness decreases. This I-DD model shows great potential in predicting and optimizing the mechanical properties of MNCs"--Abstract, page iv.
Author: Siegfried Schmauder
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 3110412454
Category : Science
Languages : en
Pages : 346
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Book Description
This book presents current spatial and temporal multiscaling approaches of materials modeling. Recent results demonstrate the deduction of macroscopic properties at the device and component level by simulating structures and materials sequentially on atomic, micro- and mesostructural scales. The book covers precipitation strengthening and fracture processes in metallic alloys, materials that exhibit ferroelectric and magnetoelectric properties as well as biological, metal-ceramic and polymer composites. The progress which has been achieved documents the current state of art in multiscale materials modelling (MMM) on the route to full multi-scaling. Contents: Part I: Multi-time-scale and multi-length-scale simulations of precipitation and strengthening effects Linking nanoscale and macroscale Multiscale simulations on the coarsening of Cu-rich precipitates in α-Fe using kinetic Monte Carlo, Molecular Dynamics, and Phase-Field simulations Multiscale modeling predictions of age hardening curves in Al-Cu alloys Kinetic Monte Carlo modeling of shear-coupled motion of grain boundaries Product Properties of a two-phase magneto-electric composite Part II: Multiscale simulations of plastic deformation and fracture Niobium/alumina bicrystal interface fracture Atomistically informed crystal plasticity model for body-centred cubic iron FE2AT ・ finite element informed atomistic simulations Multiscale fatigue crack growth modeling for welded stiffened panels Molecular dynamics study on low temperature brittleness in tungsten single crystals Multi scale cellular automata and finite element based model for cold deformation and annealing of a ferritic-pearlitic microstructure Multiscale simulation of the mechanical behavior of nanoparticle-modified polyamide composites Part III: Multiscale simulations of biological and bio-inspired materials, bio-sensors and composites Multiscale Modeling of Nano-Biosensors Finite strain compressive behaviour of CNT/epoxy nanocomposites Peptide・zinc oxide interaction
Author: Silvia Elena Barbosa
Publisher: Academic Press
ISBN: 0128122579
Category : Technology & Engineering
Languages : en
Pages : 337
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Book Description
Starch-Based Materials in Food Packaging: Processing, Characterization and Applications comprises an experimental approach related to the processing and characterization of biopolymers derived from different starches. The book includes fundamental knowledge and practical applications, and it also covers valuable experimental case studies. The book not only provides a comprehensive overview concerning biodegradable polymers, but also supplies the new trends in their applications in food packaging. The book is focused toward an ecological proposal to partially replace synthetics polymers arising from non-renewable sources for specific applications. This tender implies the protection of natural resources. Thus, the use of starch as feedstock to develop biodegradable materials is a good and promissory alternative. With the contributions and collaboration of experts in the development and study of starch based materials, this book demonstrates the versatility of this polysaccharide and its potential use. Brings the latest advances in the development of biomaterials from different starches, applying several technologies at laboratory and semi-industrial scales Examines the effect of formulations and processing conditions on structural and final properties of starch-based materials (blends and composites) Discusses the potential applications of starch materials in different fields, especially in food packaging Includes chapters on active and intelligent food packages
Author: James A. Stewart
Publisher:
ISBN: 9781267496461
Category : Lubrication and lubricants
Languages : en
Pages : 202
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Book Description
Molybdenum disulphide (MoS2) is a layered, hexagonal crystal that has a very low coefficient of friction. Due to this low coefficient of friction, MoS2 has become a well-known solid lubricant and liquid lubricant additive. As such, nanoparticles of MoS2 have been proposed as an additive to traditional liquid lubricants to provide frictional properties that are sensitive to different temperature and pressure regimes. However, to properly design these MoS2 nanoparticles to be sensitive to different temperature and pressure regimes, it is necessary to understand the mechanical response of crystalline MoS2 under mechanical loading. Specifically, the fundamental mechanism associated with the nucleation and interaction of defects as well as intralayer fracture. This thesis addressed the mechanical response of crystalline MoS2 via contact deformation (nanoindentation) simulations, which is representative of the loading conditions experienced by these nanoparticles during synthesis and application. There are two main tasks to this thesis. First, a Mo-S interatomic potential (a combination of the reactive empirical bond-order (REBO) interatomic potential and the Lennard-Jones 12-6 interatomic potential) that has been parameterized specifically to investigate the tribological properties of MoS2 was implemented into the classical molecular simulation package, LAMMPS, and refined to provide improved predictions for the mechanical properties of MoS2 via molecular statics calculations. Second, using this newly implemented interatomic potential, molecular statics calculations were performed to investigate the mechanical response of MoS2 via nanoindentation with specific focus on the nucleation of defects. Nanoindentation force - displacement curves were compared to the Hertzian contact theory prediction. It was shown that MoS2 does not follow the Hertzian prediction due it anisotropic nature. In addition, it was shown that the initial sudden force drop event in the force - displacement curves corresponds to plastic deformation. It was hypothesized that the mechanism associated with plastic failure of MoS 2 was the occurrence of broken bonds. However, it was proven that this initial plastic yield does not correspond to the occurrence of broken bonds in the MoS2 lattice; instead, a permanent slip occurred within or between the MoS2 layers.
Author: Akarsh Verma
Publisher: Springer Nature
ISBN: 9811930929
Category : Technology & Engineering
Languages : en
Pages : 395
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Book Description
This book describes the forcefields/interatomic potentials that are used in the atomistic-scale and molecular dynamics simulations. It covers mechanisms, salient features, formulations, important aspects and case studies of various forcefields utilized for characterizing various materials (such as nuclear materials and nanomaterials) and applications. This book gives many help to students and researchers who are studying the forcefield potentials and introduces various applications of atomistic-scale simulations to professors who are researching molecular dynamics.
Author: Bourama Toni
Publisher: Springer Science & Business Media
ISBN: 1461463459
Category : Mathematics
Languages : en
Pages : 296
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Book Description
This volume contains the invited contributions to the Spring 2012 seminar series at Virginia State University on Mathematical Sciences and Applications. It is a thematic continuation of work presented in Volume 24 of the Springer Proceedings in Mathematics & Statistics series. Contributors present their own work as leading researchers to advance their specific fields and induce a genuine interdisciplinary interaction. Thus all articles therein are selective, self-contained, and are pedagogically exposed to foster student interest in science, technology, engineering and mathematics, stimulate graduate and undergraduate research, as well as collaboration between researchers from different areas. The volume features new advances in mathematical research and its applications: anti-periodicity; almost stochastic difference equations; absolute and conditional stability in delayed equations; gamma-convergence and applications to block copolymer morphology; the dynamics of collision and near-collision in celestial mechanics; almost and pseudo-almost limit cycles; rainbows in spheres and connections to ray, wave and potential scattering theory; null-controllability of the heat equation with constraints; optimal control for systems subjected to null-controllability; the Galerkin method for heat transfer in closed channels; wavelet transforms for real-time noise cancellation; signal, image processing and machine learning in medicine and biology; methodology for research on durability, reliability, damage tolerance of aerospace materials and structures at NASA Langley Research Center. The volume is suitable and valuable for mathematicians, scientists and research students in a variety of interdisciplinary fields, namely physical and life sciences, engineering and technology including structures and materials sciences, computer science for signal, image processing and machine learning in medicine.
Author: Murat Tiryakioğlu
Publisher: Springer
ISBN: 3030060349
Category : Technology & Engineering
Languages : en
Pages : 386
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Book Description
This book contains a collection of papers on the science, engineering, and technology of shape casting, with contributions from researchers worldwide. Among the topics that are addressed are the structure-property-performance relationships, modeling of casting processes, and the effect of casting defects on the mechanical properties of cast alloys.
Author: A. S. Argon
Publisher: Cambridge University Press
ISBN: 0521821843
Category : Science
Languages : en
Pages : 535
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Book Description
A physical, mechanism-based presentation of the plasticity and fracture of polymers, covering industrial scale applications through to nanoscale biofluidic devices.
Author: G.C. Sih
Publisher: Springer Science & Business Media
ISBN: 1402050623
Category : Science
Languages : en
Pages : 467
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Book Description
For the first time, a book is being edited to address how results from one scale can be shifted or related to another scale, say from macro to micro or vice versa. The new approach retains the use of the equilibrium mechanics within a scale level such that cross scale results can be connected by scale invariant criteria. Engineers in different disciplines should be able to understand and use the results.
