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dc.contributor.advisorZbib, Hussein M.
dc.creatorAskari, Hesam Aldin
dc.date.accessioned2014-09-11T17:11:38Z
dc.date.available2014-09-11T17:11:38Z
dc.date.issued2014
dc.identifier.urihttp://hdl.handle.net/2376/5087
dc.descriptionThesis (Ph.D.), School of Mechanical and Materials Engineering, Washington State Universityen_US
dc.description.abstractThe objective of this research is to investigate the mechanical response of polycrystals in different settings to identify the mechanisms that give rise to specific response observed in the deformation process. Particularly the large deformation of magnesium alloys and yield properties of copper in small scales are investigated. We develop a continuum dislocation dynamics framework based on dislocation mechanisms and interaction laws and implement this formulation in a viscoplastic self-consistent scheme to obtain the mechanical response in a polycrystalline system. The versatility of this method allows various applications in the study of problems involving large deformation, study of microstructure and its evolution, superplasticity, study of size effect in polycrystals and stochastic plasticity. The findings from the numerical solution are compared to the experimental results to validate the simulation results. We apply this framework to study the deformation mechanisms in magnesium alloys at moderate to fast strain rates and room temperature to 450 °C. Experiments for the same range of strain rates and temperatures were carried out to obtain the mechanical and material properties, and to compare with the numerical results. The numerical approach for magnesium is divided into four main steps; 1) room temperature unidirectional loading 2) high temperature deformation without grain boundary sliding 3) high temperature with grain boundary sliding mechanism 4) room temperature cyclic loading. We demonstrate the capability of our modeling approach in prediction of mechanical properties and texture evolution and discuss the improvement obtained by using the continuum dislocation dynamics method. The framework was also applied to nano-sized copper polycrystals to study the yield properties at small scales and address the observed yield scatter. By combining our developed method with a Monte Carlo simulation approach, the stochastic plasticity at small length scales was studied and the sources of the uncertainty in the polycrystalline structure are discussed. Our results suggest that the stochastic response is mainly because of a) stochastic plasticity due to dislocation substructure inside crystals and b) the microstructure of the polycrystalline material. The extent of the uncertainty is correlated to the "effective cell length" in the sampling procedure whether using simulations and experimental approach.en_US
dc.description.sponsorshipSchool of Mechanical and Materials Engineering, Washington State Universityen_US
dc.language.isoEnglish
dc.rightsIn copyright
dc.rightsPublicly accessible
dc.rightsopenAccess
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.rights.urihttp://www.ndltd.org/standards/metadata
dc.rights.urihttp://purl.org/eprint/accessRights/OpenAccess
dc.subjectMechanical engineeringen_US
dc.subjectMaterials Scienceen_US
dc.subjectDislocationsen_US
dc.subjectFatigueen_US
dc.subjectGrain boundaryen_US
dc.subjectPlasticityen_US
dc.subjectPolycrystalsen_US
dc.subjectStochastic plasticityen_US
dc.titleA CONTINUUM DISLOCATION DYNAMICS FRAMEWORK FOR PLASTICITY OF POLYCRYSTALLINE MATERIALS
dc.typeElectronic Thesis or Dissertation


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