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Simulation and Modeling of Glasses: ...

Alix-Williams, Darius D.

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Simulation and Modeling of Glasses: Analysis of Structure and Mechanical Response at Various Length Scales.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Simulation and Modeling of Glasses: Analysis of Structure and Mechanical Response at Various Length Scales./
作者:	Alix-Williams, Darius D.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
面頁冊數:	196 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-07, Section: B.
Contained By:	Dissertations Abstracts International81-07B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27606993
ISBN:	9781687994820

Simulation and Modeling of Glasses: Analysis of Structure and Mechanical Response at Various Length Scales.
Alix-Williams, Darius D.

Simulation and Modeling of Glasses: Analysis of Structure and Mechanical Response at Various Length Scales. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 196 p.

Source: Dissertations Abstracts International, Volume: 81-07, Section: B.

Thesis (Ph.D.)--The Johns Hopkins University, 2019.

This item must not be sold to any third party vendors.

We use simulation and theoretical modeling to study the structure and mechanical behavior of glasses. We propose a computational methodology for measuring effective temperature in simulated glasses using thermodynamic integration. A glass is decomposed into coupled thermal subsystems containing the slow configurational and fast kinetic/vibrational degrees of freedom. The inherent structure contains the slow degrees of freedom and is obtained from energy minimization in simulation. The fast degrees of freedom are determined from the difference between the internal energy and inherent structure energy at a given temperature. We analyze subsystem energy fluctuations at different length scales throughout the quench. We integrate parameters derived from energy fluctuations with respect to reservoir temperature to determine the effective temperature. Above the glass transition the effective temperatures of simulated glasses prepared at different quench rates are all in equilibrium with the reservoir; however, systems fall out of equilibrium in order of decreasing quench rate below it.We then simulate plasticity in sheared glasses and develop a model for the growth of shear bands as a function of applied strain. Shear bands are modeled as pulled fronts that propagate into an unsteady state. Effective temperature shear-transformation-zone (ET-STZ) theory models the structural state of material on either side of the front. Simulated shear bands broaden to encompass the entire simulation cell or to finite width within the simulation cell. Our model captures this behavior both at the early and late stages of band broadening. In the early stages the rate of band broadening is solely a function of strain rate within the band. This result suggests that a single timescale related to the shear rate inside the band dominates material response at low strain, but this is counterbalanced by thermal relaxation which sets the band width at large strain.We conclude with a study of a parameter optimization protocol which seeks to minimize the difference in model response between a molecular dynamics (MD) simulation of shear deformation in a metallic glass and a continuum mechanics (CM) model for glassy plasticity based on ET-STZ theory. The optimizer searches for the best parameters to linearly map a coarse-grained MD initial potential energy field onto an effective temperature field used as the initial state of the CM model. We explore the optimal mapping parameters recovered as we vary the comparison metric used by the optimizer when evaluating the difference between MD and CM model response.

ISBN: 9781687994820Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Shear banding

Simulation and Modeling of Glasses: Analysis of Structure and Mechanical Response at Various Length Scales.
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520 $a We use simulation and theoretical modeling to study the structure and mechanical behavior of glasses. We propose a computational methodology for measuring effective temperature in simulated glasses using thermodynamic integration. A glass is decomposed into coupled thermal subsystems containing the slow configurational and fast kinetic/vibrational degrees of freedom. The inherent structure contains the slow degrees of freedom and is obtained from energy minimization in simulation. The fast degrees of freedom are determined from the difference between the internal energy and inherent structure energy at a given temperature. We analyze subsystem energy fluctuations at different length scales throughout the quench. We integrate parameters derived from energy fluctuations with respect to reservoir temperature to determine the effective temperature. Above the glass transition the effective temperatures of simulated glasses prepared at different quench rates are all in equilibrium with the reservoir; however, systems fall out of equilibrium in order of decreasing quench rate below it.We then simulate plasticity in sheared glasses and develop a model for the growth of shear bands as a function of applied strain. Shear bands are modeled as pulled fronts that propagate into an unsteady state. Effective temperature shear-transformation-zone (ET-STZ) theory models the structural state of material on either side of the front. Simulated shear bands broaden to encompass the entire simulation cell or to finite width within the simulation cell. Our model captures this behavior both at the early and late stages of band broadening. In the early stages the rate of band broadening is solely a function of strain rate within the band. This result suggests that a single timescale related to the shear rate inside the band dominates material response at low strain, but this is counterbalanced by thermal relaxation which sets the band width at large strain.We conclude with a study of a parameter optimization protocol which seeks to minimize the difference in model response between a molecular dynamics (MD) simulation of shear deformation in a metallic glass and a continuum mechanics (CM) model for glassy plasticity based on ET-STZ theory. The optimizer searches for the best parameters to linearly map a coarse-grained MD initial potential energy field onto an effective temperature field used as the initial state of the CM model. We explore the optimal mapping parameters recovered as we vary the comparison metric used by the optimizer when evaluating the difference between MD and CM model response.
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