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Author: Dmitrii Ilin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In the present work, we establish a one-way coupled crystal plasticity - hydrogen diffusion analysis and use this approach to study the hydrogen transport in artificial polycrystalline aggregates of 316L steel with different grain geometries and crystallographic orientation. The data about stress/strain fields computed at the microstructure scaleutilizing the crystal plasticity concept are transferred to the in-house diffusion code which was developed using a new numerical scheme for solving parabolic equations. In the case of initial uniform hydrogen content, the heterogeneity of the mechanical fields is shownto induce a redistribution of hydrogen in the microstructure. The effect of strain rate is clearly revealed. In the second part, hydrogen transport across grain boundaries is investigatedconsidering the specific diffusivity and segregation properties of these interfaces. Using a discrete atomic layer model, the retarding impact of grain boundaries is demonstrated on bicrystals and bamboo type membranes with and without external mechanical loading. To reproduce the effects observed in the atomistic simulations into the crystal plasticity - hydrogen diffusion model, a new physically based multi-scale method is proposed. Using this new approach we study the effect of grain boundary trapping kinetics on hydrogen diffusion and reveal a new grain boundary diffusion regime which has notbeen reported before.
Author: Dmitrii Ilin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
In the present work, we establish a one-way coupled crystal plasticity - hydrogen diffusion analysis and use this approach to study the hydrogen transport in artificial polycrystalline aggregates of 316L steel with different grain geometries and crystallographic orientation. The data about stress/strain fields computed at the microstructure scaleutilizing the crystal plasticity concept are transferred to the in-house diffusion code which was developed using a new numerical scheme for solving parabolic equations. In the case of initial uniform hydrogen content, the heterogeneity of the mechanical fields is shownto induce a redistribution of hydrogen in the microstructure. The effect of strain rate is clearly revealed. In the second part, hydrogen transport across grain boundaries is investigatedconsidering the specific diffusivity and segregation properties of these interfaces. Using a discrete atomic layer model, the retarding impact of grain boundaries is demonstrated on bicrystals and bamboo type membranes with and without external mechanical loading. To reproduce the effects observed in the atomistic simulations into the crystal plasticity - hydrogen diffusion model, a new physically based multi-scale method is proposed. Using this new approach we study the effect of grain boundary trapping kinetics on hydrogen diffusion and reveal a new grain boundary diffusion regime which has notbeen reported before.
Author: Bachir Osman Hoch
Publisher:
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Languages : en
Pages : 0
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The diffusion of hydrogen in metals is a key factor for understanding the basic mechanisms of hydrogen embrittlement. However, the contribution of grain boundaries to the hydrogen diffusion is not well established. In this this work, we first investigated the effects of a heterogeneous grain boundary networks on the effective diffusivity in polycrystalline materials, using finite elements modeling. To do so, hydrogen diffusion through heterogeneous materials, modeled by a ternary continuum composite media, was simulated. We showed, by characterizing the grain-boundary connectivity, that there are strong correlations between the grain-boundary connectivity parameters and the effective diffusivity. It was found also that these correlations are more significant for nanocrystalline materials. Moreover, by using a homogenization method, it was evidenced that the percolation behavior of the effective diffusivity is controlled by the grain-boundary network evolution, without exhibiting the same percolation threshold than the latter. A second approach, using EBSD-based microstructures, was conducted to evaluate the effect of microstructural constraints on the grain boundary connectivity and to compare the effective diffusivity numerically obtained with experimental data on polycrystalline nickel from literature. In parallel, experimental analyses were performed to analyze the effects of the grain boundaries on the local hydrogen concentration. This highlighted the significant impact of grain-boundary character on the hydrogen distribution around grain boundaries, which can not be explained by the only diffusion process.
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Author: Prasanna Kumar Bhargav Indurthi
Publisher:
ISBN:
Category : Hydrogen
Languages : en
Pages : 170
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Author:
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ISBN:
Category :
Languages : en
Pages : 10
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In this study, hydrogen diffusion impacts the performance of solid-state hydrogen storage materials and contributes to the embrittlement of structural materials under hydrogen-containing environments. In atomistic simulations, the diffusion energy barriers are usually calculated using molecular statics simulations where a nudged elastic band method is used to constrain a path connecting the two end points of an atomic jump. This approach requires prior knowledge of the "end points". For alloy and defective systems, the number of possible atomic jumps with respect to local atomic configurations is tremendous. Even when these jumps can be exhaustively studied, it is still unclear how they can be combined to give an overall diffusion behavior seen in experiments. Here we describe the use of molecular dynamics simulations to determine the overall diffusion energy barrier from the Arrhenius equation. This method does not require information about atomic jumps, and it has additional advantages, such as the ability to incorporate finite temperature effects and to determine the pre-exponential factor. As a test case for a generic method, we focus on hydrogen diffusion in bulk aluminum. We find that the challenge of this method is the statistical variation of the results. However, highly converged energy barriers can be achieved by an appropriate set of temperatures, output time intervals (for tracking hydrogen positions), and a long total simulation time. Our results help elucidate the inconsistencies of the experimental diffusion data published in the literature. The robust approach developed here may also open up future molecular dynamics simulations to rapidly study diffusion properties of complex material systems in multidimensional spaces involving composition and defects.
Author: Mahesh Naalla
Publisher:
ISBN:
Category : Hydrogen
Languages : en
Pages : 138
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Author: G. Alefeld
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 420
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Author: Ioan R. Ionescu
Publisher: John Wiley & Sons
ISBN: 1119687543
Category : Science
Languages : en
Pages : 243
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Book Description
Chronicling the 11th US France Mechanics and physics of solids at macro- and nano-scales symposium, organized by ICACM (International Center for Applied Computational Mechanics) in Paris, June 2018, this book addresses the breadth of issues raised. It covers a comprehensive range of scientific and technological topics (from elementary plastic events in metals and materials in harsh environments to bio-engineered and bio-mimicking materials), offering a representative perspective on state-of-the-art research and materials. Expounding on the issues related to mesoscale modeling, the first part of the book addresses the representation of plastic deformation at both extremes of the scale between nano- and macro- levels. The second half of the book examines the mechanics and physics of soft materials, polymers and materials made from fibers or molecular networks.
Author: D.J. Fisher
Publisher: Trans Tech Publications Ltd
ISBN: 3038266507
Category : Technology & Engineering
Languages : en
Pages : 266
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Book Description
The Monte Carlo method, largely the brainchild of Stanislaw Ulam and first implemented by John von Neumann, depends upon the use of digital computers and is therefore very much a product of post-WW2 technological developments; even though one could argue that the Buffons Needle estimate was an ancestor of the technique. The probabilistic nature of the method makes it a good choice for modeling those physical phenomena which involve similarly random motions at the atomic scale; a particularly good example being that of mass diffusion. The present volume comprises a compilation of selected Monte Carlo studies of diffusion in borides, carbides, diamond, graphene, graphite, hydrides, ice, metals, oxides, semiconductors, sulfides, zeolites and other materials. General aspects of diffusion are also covered. The 516 entries cover the period from 1966 to 2014.
Author: Siegfried Schmauder
Publisher: Springer
ISBN: 9789811068836
Category : Science
Languages : en
Pages : 0
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This book provides a comprehensive reference for the studies of mechanical properties of materials over multiple length and time scales. The topics include nanomechanics, micromechanics, continuum mechanics, mechanical property measurements, and materials design. The handbook employs a consistent and systematic approach offering readers a user friendly reference ideal for frequent consultation. It is appropriate for an audience at of graduate students, faculties, researchers, and professionals in the fields of Materials Science, Mechanical Engineering, Civil Engineering, Engineering Mechanics, and Aerospace Engineering.
Author: Urban Engberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 68
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