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Numerical Modeling of Plasticity in FCC Crystalline Materials Using Discrete Dislocation Dynamics
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.ORCID iD: 0000-0001-5059-1791
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Plasticity in crystalline solids is controlled by the microscopic line defects known as “dislocations”. Decisive role of dislocations in crystal plasticity in addition to fundamentals of plastic deformation are presented in the current thesis work. Moreover, major features of numerical modeling method “Discrete Dislocation Dynamics (DDD)” technique are described to elucidate a powerful computational method used in simulation of crystal plasticity.

First part of the work is focused on the investigation of strain rate effect on the dynamic deformation of crystalline solids. Single crystal copper is chosen as a model crystal and discrete dislocation dynamics method is used to perform numerical uniaxial tensile test on the single crystal at various high strain rates. Twenty four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1 µm subjected to periodic boundary conditions. Loading of the model crystal with the considered initial dislocation microstructure at constant strain rates ranging from 103 to 105s1 leads to a significant strain rate sensitivity of the plastic flow. In addition to the flow stress, microstructure evolution of the sample crystal demonstrates a considerable strain rate dependency. Furthermore, strain rate affects the strain induce microstructure heterogeneity such that more heterogeneous microstructure emerges as strain rate increases.

Anisotropic characteristic of plasticity in single crystals is investigated in the second part of the study. Copper single crystal is selected to perform numerical tensile tests on the model crystal along two different loading directions of [001] and [111] at two high strain rates. Effect of loading orientation on the macroscopic behavior along with microstructure evolution of the model crystal is examined using DDD method. Investigation of dynamic response of single crystal to the mechanical loading demonstrates a substantial effect of loading orientation on the flow stress. Furthermore, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Likewise, strain induced microstructure heterogeneity displays the effect of loading direction such that more heterogeneous microstructure evolve as single crystal is loaded along [111] direction. Formation of slip bands and consequently localization of plastic deformation are detected as model crystal is loaded along both directions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , x, 50 p.
Keyword [en]
Dislocations, crystal plasticity, discrete dislocation dynamics, Cu single crystal, high strain rate deformation, strain rate sensitivity, plastic anisotropy, slip band formation
National Category
Engineering and Technology Materials Engineering Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-175424ISBN: 978-91-7595-705-0 (print)OAI: oai:DiVA.org:kth-175424DiVA: diva2:860893
Presentation
2015-10-22, Sal Kuben N111, Brinellvägen 23, Materialvetenskap, KTH, Stockholm, 15:30 (English)
Opponent
Supervisors
Note

QC 20151015

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved
List of papers
1. Investigation of loading orientation effect on dynamic deformation of single crystal copper at high strain rates: Discrete dislocation dynamics study
Open this publication in new window or tab >>Investigation of loading orientation effect on dynamic deformation of single crystal copper at high strain rates: Discrete dislocation dynamics study
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Uniaxial tensile loading of copper single crystal along [001] and [111] orientations is modeled at two high strain rates of 105 and 106 s-1. Discrete dislocation dynamics method is used to study the anisotropic characteristic of plastic deformation in the model crystal. Furthermore, strain rate sensitivity of the flow stress in copper crystal is examined. Investigation of mechanical response of single crystal to the external loading demonstrates a substantial effect of loading orientation on the plastic flow. We find that at both imposed strain rates flow stress increases significantly when tensile load is applied along [111] crystallographic axis. Similarly, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Moreover, plastic flow behavior exhibits a profound strain rate sensitivity at both loading orientations which agrees well with experimental observations regarding strain rate dependency of flow stress in copper single crystal as strain rate exceeds 103 s-1. At both applied strain rates dislocations evolve into a heterogeneous microstructure and highest heterogeneity is observed as model crystal is loaded along [111] direction at strain rate of    106 s-1. Formation of slip bands and consequently localization of plastic deformation are detected for all considered cases. However, at the higher strain rate of 106 s-1, slip band formation is more pronounced for both loading orientations.

Keyword
Discrete dislocation dynamics, Crystal plasticity, Plastic anisotropy, Cu single crystal, High strain rate deformation, Slip band formation
National Category
Materials Engineering Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-175414 (URN)
Note

QS 2015

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved
2. Three-dimensional dislocation dynamics simulation of plastic deformation in copper single crystal
Open this publication in new window or tab >>Three-dimensional dislocation dynamics simulation of plastic deformation in copper single crystal
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dynamic deformation of single crystal copper at high strain rates ranging from 103 to 105 s-1 is modeled using three dimensional discrete dislocation dynamics method. Numerical uniaxial tensile test is performed on a model crystal along [0 0 1] orientation to examine the resulting macroscopic behavior along with microstructure evolution at high strain rates. Twenty-four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1  subjected to period boundary conditions. In the simulated single crystal with the considered initial dislocation microstructure, plastic flow demonstrates a significant strain rate dependency at imposed strain rates. Rate sensitivity of flow stress observed at strain rates >> 103 s-1 agrees well with the reported experimental studies on copper single crystal.  Furthermore, strain rate considerably affects the microstructure evolution of the sample crystal as a result of influence of strain rate on dislocations generation and interactions. Formation of heterogeneous microstructure is observed at all imposed strain rates. We find that heterogeneity of microstructure escalates as strain rate increases.

Keyword
Dislocation dynamics, plastic deformation, Cu single crystal, high strain rate deformation
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-175413 (URN)
Funder
Natural‐Disaster Science
Note

QS 2015

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved

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