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Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database./
作者:	Akhondzadeh, Shamseddin.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	153 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-07, Section: B.
Contained By:	Dissertations Abstracts International83-07B.
標題:	Yield stress. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28483303
ISBN:	9798505571682

Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database.
Akhondzadeh, Shamseddin.

Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 153 p.

Source: Dissertations Abstracts International, Volume: 83-07, Section: B.

Thesis (Ph.D.)--Stanford University, 2021.

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

Most metals are crystalline materials that can undergo significant plastic (permanent) deformation when subjected to applied loading. Plastic deformation is usually accompanied by an increase in the flow stress of the material. This phenomenon is called strain hardening and is of vital importance in many engineering applications, including aerospace, automotive, and power generation industries. Developing accurate material models to predict the plastic response and hardening behavior of metals during deformation is a prerequisite to the engineering design processes, which requires a physical understanding of the underlying deformation mechanisms. In single crystals, plastic deformation of the crystal is governed by the evolution of dislocations---line defects inside the crystalline materials which marks the boundary between the slipped and unslipped regions---moving and interacting in response to the applied loading. Dislocation dynamics (DD) simulations, which track the time-space trajectories of individual dislocation lines, provide a promising tool to establish a physical link between the dislocation microstructure evolution and the strain hardening phenomenon. However, the high computational cost of DD simulations renders the accessible length and time scales to well below those which are relevant to most engineering applications. Due to this challenge, instead of directly using DD simulations for engineering applications, we have utilized DD simulations to delineate how constitutive relations of crystal plasticity (CP) can be constructed for FCC copper, based on coarse-graining of high-throughput DD simulations. This thesis consists of three main components, and we show how they fit together into a complete, physical model like three pieces of a puzzle. The first piece is a massive DD simulation database that we were able to generate thanks to recent computational advances in DD, including the subcycling time-integration algorithm and its implementation on Graphics Processing Units (GPUs). By systematically coarse-graining the database we present a strain hardening model which consists of two components: 1) a dislocation multiplication model, which accounts for slip-free multiplication, and 2) an exponential flow-rule connecting slip system shear rate γi to the resolved shear stress τi through an exponential function. These components can be thought of as the second and third puzzle pieces. By analyzing the data, it was discovered that dislocation multiplication frequently occurs on slip systems which experience zero applied shear stress (i.e., zero Schmid factor) and have a plastic strain rate of zero; we termed such multiplication slip-free multiplication and it serves as the second puzzle piece. This finding questions the assumption of the existing phenomenological expression that multiplication ( ˙ρi) is proportional to the shear rate γi. We propose to add a correction term to the generalized Kocks-Mecking expression to account for slip-free multiplication, whose mechanistic explanation is provided. A major finding of this thesis is that DD results suggest an exponential flow-rule, in contrast to the commonly used power-law flow-rule, even in the cases where thermal fluctuations are not present. The exponential flow-rule is the third piece in the puzzle of the presented strain hardening model. We demonstrate that the observed exponential flow-rule, despite the common notion that thermal fluctuations are the responsible mechanism, can be explained by statistical properties of the dislocation links. Hence, by statistically analyzing the number density and plastic activity of links in terms of their length, we formulate a physically justified link length based flow rule which can numerically capture the exponential dependence of γi on τi.

ISBN: 9798505571682Subjects--Topical Terms:

3561163
Yield stress.

Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database.
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245 1 0 $a Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database.
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300 $a 153 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-07, Section: B.
500 $a Advisor: Cai, Wei; Darve, Eric; Lew, Adrian; Nix, William D.
502 $a Thesis (Ph.D.)--Stanford University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Most metals are crystalline materials that can undergo significant plastic (permanent) deformation when subjected to applied loading. Plastic deformation is usually accompanied by an increase in the flow stress of the material. This phenomenon is called strain hardening and is of vital importance in many engineering applications, including aerospace, automotive, and power generation industries. Developing accurate material models to predict the plastic response and hardening behavior of metals during deformation is a prerequisite to the engineering design processes, which requires a physical understanding of the underlying deformation mechanisms. In single crystals, plastic deformation of the crystal is governed by the evolution of dislocations---line defects inside the crystalline materials which marks the boundary between the slipped and unslipped regions---moving and interacting in response to the applied loading. Dislocation dynamics (DD) simulations, which track the time-space trajectories of individual dislocation lines, provide a promising tool to establish a physical link between the dislocation microstructure evolution and the strain hardening phenomenon. However, the high computational cost of DD simulations renders the accessible length and time scales to well below those which are relevant to most engineering applications. Due to this challenge, instead of directly using DD simulations for engineering applications, we have utilized DD simulations to delineate how constitutive relations of crystal plasticity (CP) can be constructed for FCC copper, based on coarse-graining of high-throughput DD simulations. This thesis consists of three main components, and we show how they fit together into a complete, physical model like three pieces of a puzzle. The first piece is a massive DD simulation database that we were able to generate thanks to recent computational advances in DD, including the subcycling time-integration algorithm and its implementation on Graphics Processing Units (GPUs). By systematically coarse-graining the database we present a strain hardening model which consists of two components: 1) a dislocation multiplication model, which accounts for slip-free multiplication, and 2) an exponential flow-rule connecting slip system shear rate γi to the resolved shear stress τi through an exponential function. These components can be thought of as the second and third puzzle pieces. By analyzing the data, it was discovered that dislocation multiplication frequently occurs on slip systems which experience zero applied shear stress (i.e., zero Schmid factor) and have a plastic strain rate of zero; we termed such multiplication slip-free multiplication and it serves as the second puzzle piece. This finding questions the assumption of the existing phenomenological expression that multiplication ( ˙ρi) is proportional to the shear rate γi. We propose to add a correction term to the generalized Kocks-Mecking expression to account for slip-free multiplication, whose mechanistic explanation is provided. A major finding of this thesis is that DD results suggest an exponential flow-rule, in contrast to the commonly used power-law flow-rule, even in the cases where thermal fluctuations are not present. The exponential flow-rule is the third piece in the puzzle of the presented strain hardening model. We demonstrate that the observed exponential flow-rule, despite the common notion that thermal fluctuations are the responsible mechanism, can be explained by statistical properties of the dislocation links. Hence, by statistically analyzing the number density and plastic activity of links in terms of their length, we formulate a physically justified link length based flow rule which can numerically capture the exponential dependence of γi on τi.
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