A discrete dislocation dynamics framework for polycrystalline materials

Polycrystalline materials with mean grain size smaller than 10nm will soften if its mean grain size is further reduced, deviating from Hall-Petch relation which states that yield strength is inversely proportional to square root of mean grain size. Besides, polycrystalline materials with identical m...

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Main Author: Chooi, Zheng Hoe
Other Authors: Wu Mao See
Format: Final Year Project
Language:English
Published: 2015
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Online Access:http://hdl.handle.net/10356/62089
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-620892023-03-04T18:41:04Z A discrete dislocation dynamics framework for polycrystalline materials Chooi, Zheng Hoe Wu Mao See School of Mechanical and Aerospace Engineering A*STAR Institute of High Performance Computing DRNTU::Engineering Polycrystalline materials with mean grain size smaller than 10nm will soften if its mean grain size is further reduced, deviating from Hall-Petch relation which states that yield strength is inversely proportional to square root of mean grain size. Besides, polycrystalline materials with identical mean grain size but different grain size distribution also shown to have different strength. These phenomena suggested that average grain size is not the only factor that determines the strength of polycrystals. This project aims to expand the current discrete dislocation dynamics (DDD) model to investigate the causes of the deviation in Hall-Petch relation. First, the DDD model was modified to allow simulations on arbitrary grain shapes. Simulation results showed that Johnson-Mehl microstructure (wider grain size distribution) is weaker than site-saturation microstructure (narrower grain size distribution), despite both having identical average grain size. This showed that grain size distribution does affect the strength of polycrystals. The presence of relatively larger grains in Johnson-Mehl microstructure allowed more dislocation pile up, resulting in higher plastic strain. Next, the DDD model was further expanded to incorporate grain boundary deformations. Using this model and removing influences of lattice dislocation, preliminary results obtained from regular hexagonal microstructure with grain size of 10nm was shown to be weaker than that of 20nm and 40nm. In this case, reducing grain size increased grain boundary density, consequently allowed more grain boundary deformation, weakening the material. Results obtained from the modified DDD framework are in line with experimental findings. Bachelor of Engineering (Mechanical Engineering) 2015-01-13T08:11:44Z 2015-01-13T08:11:44Z 2014 2014 Final Year Project (FYP) http://hdl.handle.net/10356/62089 en Nanyang Technological University 46 p. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic DRNTU::Engineering
spellingShingle DRNTU::Engineering
Chooi, Zheng Hoe
A discrete dislocation dynamics framework for polycrystalline materials
description Polycrystalline materials with mean grain size smaller than 10nm will soften if its mean grain size is further reduced, deviating from Hall-Petch relation which states that yield strength is inversely proportional to square root of mean grain size. Besides, polycrystalline materials with identical mean grain size but different grain size distribution also shown to have different strength. These phenomena suggested that average grain size is not the only factor that determines the strength of polycrystals. This project aims to expand the current discrete dislocation dynamics (DDD) model to investigate the causes of the deviation in Hall-Petch relation. First, the DDD model was modified to allow simulations on arbitrary grain shapes. Simulation results showed that Johnson-Mehl microstructure (wider grain size distribution) is weaker than site-saturation microstructure (narrower grain size distribution), despite both having identical average grain size. This showed that grain size distribution does affect the strength of polycrystals. The presence of relatively larger grains in Johnson-Mehl microstructure allowed more dislocation pile up, resulting in higher plastic strain. Next, the DDD model was further expanded to incorporate grain boundary deformations. Using this model and removing influences of lattice dislocation, preliminary results obtained from regular hexagonal microstructure with grain size of 10nm was shown to be weaker than that of 20nm and 40nm. In this case, reducing grain size increased grain boundary density, consequently allowed more grain boundary deformation, weakening the material. Results obtained from the modified DDD framework are in line with experimental findings.
author2 Wu Mao See
author_facet Wu Mao See
Chooi, Zheng Hoe
format Final Year Project
author Chooi, Zheng Hoe
author_sort Chooi, Zheng Hoe
title A discrete dislocation dynamics framework for polycrystalline materials
title_short A discrete dislocation dynamics framework for polycrystalline materials
title_full A discrete dislocation dynamics framework for polycrystalline materials
title_fullStr A discrete dislocation dynamics framework for polycrystalline materials
title_full_unstemmed A discrete dislocation dynamics framework for polycrystalline materials
title_sort discrete dislocation dynamics framework for polycrystalline materials
publishDate 2015
url http://hdl.handle.net/10356/62089
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