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dc.contributor.advisorSidney Yip.en_US
dc.contributor.authorChang, Jinpeng, 1974-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Nuclear Engineering.en_US
dc.date.accessioned2005-05-17T14:37:43Z
dc.date.available2005-05-17T14:37:43Z
dc.date.copyright2003en_US
dc.date.issued2003en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/16601
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003.en_US
dc.descriptionIncludes bibliographical references (p. 199-211).en_US
dc.descriptionThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.en_US
dc.description.abstractMultiscale materials modeling has emerged in recent years as a significant concept and the only viable approach to understand the mechanical response of materials by linking modeling research at different length scales and time scales, including quantum mechanics, atomistics modeling, mesoscale modeling and continuum modeling together. The role that atomistic modeling plays is important and indispensable in that it can generate understanding of the physics and pass this mechanistic understanding as well as important parameters to higher level simulations. This thesis presents theories and simulations of defect nucleation and mobility in BCC transition metal molybdenum using atomistic methods, with the two primary defects of interest being dislocations and deformation twinning, and emphasis on the atomistic mechanisms and measures. The contributions presented in the thesis may be regarded as advances in both methods development and mechanistic understanding of dislocation mobility and twinning nucleation. For atomistic studies of dislocations in a simulation cell of finite size, new methods have been derived to (1) calculate the atomic displacement field under PBC and generate atomic dislocation configuration from this displacement field; (2) quantify artificial image effect for a dislocation moving within the periodic cell and optimize geometry of simulation cell to minimize such effects. These methodological breakthroughs serve as the basis for atomistic studies of dislocations and are used repeatedly in this thesis. To understand the complex plasticity behavior of BCC metal molybdenum, we need to first understand the most fundamental problem of core structureen_US
dc.description.abstract(cont.) and lattice resistance of straight dislocations before considering more complicated structures including kinks, jogs, junctions, etc. In this thesis, we examine the two major types of dislocations that are of primary interest in BCC molybdenum: screw dislocations, which is the major plasticity carrier at low temperatures, and edge dislocations, which become important at elevated temperatures. For screw dislocations, the issue of whether core is polarized or not is explored by a static calculation of core structure for the first time by a tight-binding potential. The screw core structure is determined to be non-polarized; however, the magnitude of Peierls stress, which is a measure of the lattice resistance to dislocation motion and is calculated accurately using a local-driving-force method in this thesis, remains rather high despite of the non-polarized core, suggesting that core polarization is a secondary and less important effect compared to core planarity. For edge dislocations in molybdenum, the core structure and Peierls stress is calculated using a Finnis-Sinclair potential and it is shown that edge dislocation in Mo has a planar core structure and a core width of approximately 11[angstroms], is indeed very mobile and has a Peierls stress of only 25 MPa, after correction for image effects due to boundary conditions. This new result is consistent with experimental observations of high mobility of edge dislocations and clearly rejects the proposal of kink mechanisms operating on edge dislocations that arose in the literature as a result of previous inaccurate Peierls stress calculations yielding an unrealistically high value of 700 MPa ...en_US
dc.description.statementofresponsibilityby Jinpeng Chang.en_US
dc.format.extent211 p.en_US
dc.format.extent20483628 bytes
dc.format.extent20483343 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/pdf
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectNuclear Engineering.en_US
dc.titleAtomistics of defect nucleation and mobility : dislocations and twinningen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Nuclear Engineeringen_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Nuclear Science and Engineering
dc.identifier.oclc55011166en_US


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