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postgraduate thesis: Fabric evolution of two-dimensional idealized particle assemblage during shear

TitleFabric evolution of two-dimensional idealized particle assemblage during shear
Authors
Advisors
Issue Date2012
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Luo, S. [罗赛]. (2012). Fabric evolution of two-dimensional idealized particle assemblage during shear. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979972
AbstractMicrostructure or fabric definitely affects macroscopic mechanical behavior of granular material. It is also well-observed that fabric evolves with shearing or plastic deformation. In this study, a series of two-dimensional numerical direct shear tests are carried out with the discrete element method, to study the initial fabric effect on global material responses and their micro-macroscopic relations. Idealized particle assemblages are made up of mono-size elongated particles and are prepared by a “deposition” method. Elongated particle is modeled by the built-in clump logic, in which constitutive balls are joined together without further breakage. In the deposition method, there are three controlling parameters, including, deposited direction, inter-particle friction coefficient and particle number, to prepare specimens with similar initial density but different initial packing or fabric. Three types of fabric of particle assemblages are examined quantitatively and are monitored during shearing, including, particle orientations (PO), contact normal forces (NF), and void spaces (VS). These fabric distributions are described by two parameters―anisotropic degree ( ) and orientation angle ( ), with clear physical implications. An additional parameter ( ) describing the average size of voids, is used to quantify void perimeter. It is found that this parameter has a relation with the assemblage’s volumetric response. C With the systematic and meticulous quantification method, the linkage between the macroscopic and microscopic responses of particle assemblages is discussed quantitatively. The results show that the initial packing affects the shear zone thickness, initial stiffness, peak strength, and dilation rate. In the shear zone, particle orientations do not exhibit a unique state at the final stage of direct shearing. At that state, strong normal forces and strong voids are parallel to the major principal stress direction. It seems that the initial packing does not affect their final distributions. At the end of reverse shearing, strong voids and strong normal forces in the shear zone give an essentially unique state, and their preferential directions are related to the changed loading direction. However, apparent stable particle orientations are still affected by the initial fabric.
DegreeMaster of Philosophy
SubjectGranular materials - Mathematical models.
Particles - Mathematical models.
Shear (Mechanics)
Dept/ProgramCivil Engineering
Persistent Identifierhttp://hdl.handle.net/10722/181538

 

DC FieldValueLanguage
dc.contributor.advisorYan, RWM-
dc.contributor.advisorYeung, ATC-
dc.contributor.authorLuo, Sai-
dc.contributor.author罗赛-
dc.date.accessioned2013-03-03T03:21:06Z-
dc.date.available2013-03-03T03:21:06Z-
dc.date.issued2012-
dc.identifier.citationLuo, S. [罗赛]. (2012). Fabric evolution of two-dimensional idealized particle assemblage during shear. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979972-
dc.identifier.urihttp://hdl.handle.net/10722/181538-
dc.description.abstractMicrostructure or fabric definitely affects macroscopic mechanical behavior of granular material. It is also well-observed that fabric evolves with shearing or plastic deformation. In this study, a series of two-dimensional numerical direct shear tests are carried out with the discrete element method, to study the initial fabric effect on global material responses and their micro-macroscopic relations. Idealized particle assemblages are made up of mono-size elongated particles and are prepared by a “deposition” method. Elongated particle is modeled by the built-in clump logic, in which constitutive balls are joined together without further breakage. In the deposition method, there are three controlling parameters, including, deposited direction, inter-particle friction coefficient and particle number, to prepare specimens with similar initial density but different initial packing or fabric. Three types of fabric of particle assemblages are examined quantitatively and are monitored during shearing, including, particle orientations (PO), contact normal forces (NF), and void spaces (VS). These fabric distributions are described by two parameters―anisotropic degree ( ) and orientation angle ( ), with clear physical implications. An additional parameter ( ) describing the average size of voids, is used to quantify void perimeter. It is found that this parameter has a relation with the assemblage’s volumetric response. C With the systematic and meticulous quantification method, the linkage between the macroscopic and microscopic responses of particle assemblages is discussed quantitatively. The results show that the initial packing affects the shear zone thickness, initial stiffness, peak strength, and dilation rate. In the shear zone, particle orientations do not exhibit a unique state at the final stage of direct shearing. At that state, strong normal forces and strong voids are parallel to the major principal stress direction. It seems that the initial packing does not affect their final distributions. At the end of reverse shearing, strong voids and strong normal forces in the shear zone give an essentially unique state, and their preferential directions are related to the changed loading direction. However, apparent stable particle orientations are still affected by the initial fabric.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.source.urihttp://hub.hku.hk/bib/B49799721-
dc.subject.lcshGranular materials - Mathematical models.-
dc.subject.lcshParticles - Mathematical models.-
dc.subject.lcshShear (Mechanics)-
dc.titleFabric evolution of two-dimensional idealized particle assemblage during shear-
dc.typePG_Thesis-
dc.identifier.hkulb4979972-
dc.description.thesisnameMaster of Philosophy-
dc.description.thesislevelMaster-
dc.description.thesisdisciplineCivil Engineering-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b4979972-
dc.date.hkucongregation2013-

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