Virginia Tech
    • Log in
    View Item 
    •   VTechWorks Home
    • ETDs: Virginia Tech Electronic Theses and Dissertations
    • Doctoral Dissertations
    • View Item
    •   VTechWorks Home
    • ETDs: Virginia Tech Electronic Theses and Dissertations
    • Doctoral Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Modeling the Role of Surfaces and Grain Boundaries in Plastic Deformation

    Thumbnail
    View/Open
    Kuhr_BR_D_2017.pdf (5.511Mb)
    Downloads: 755
    Supporting documents (31.01Mb)
    Downloads: 72
    Supporting documents (114.6Kb)
    Downloads: 21
    Supporting documents (169.4Kb)
    Downloads: 392
    Supporting documents (67.08Kb)
    Downloads: 33
    Supporting documents (169.0Kb)
    Downloads: 41
    Date
    2017-08-15
    Author
    Kuhr, Bryan Richard
    Metadata
    Show full item record
    Abstract
    In this dissertation, simulation techniques are used to understand the role of surfaces and grain boundaries in the deformation response of metallic materials. This research utilizes atomistic scale modeling to study nanoscale deformation phenomena with time and spatial resolution not available in experimental testing. Molecular dynamics techniques are used to understand plastic deformation of grain boundaries and surfaces in metals under different configurations and loading procedures. Stress and strain localization phenomena are investigated at plastically deformed boundaries in axially strain thin film samples. Joint experimental and modelling work showed increased stress states at the intersections of slip planes and grain boundaries. This effect, as well as several other differences related to stress and strain localization are thoroughly examined in digital samples with two different grain boundary relaxation states. It is found that localized stress and strain is exacerbated by initial boundary disorder. Dislocation content in the randomly generated boundaries of these samples was quantified via the dislocation extraction algorithm. Significant numbers of lattice dislocations were present in both deformed and undeformed samples. Trends in dislocation content during straining were identified for individual samples and boundaries but were not consistent across all examples. The various contributions to dislocation content and the implications on material behavior are discussed. The effects of grain boundary hydrogen on the deformation response of a digital Ni polycrystalline thin film sample is reported. H content is found to change the structure of the boundaries and effect dislocation emission. The presence of dispersed hydrogen caused a slight increase in yield strength, followed by an increase in grain boundary dislocation emission and an increase in grain boundary crack formation and growth. An atomistic nano indenter is employed to study the nanoscale contact behavior of the indenter-surface interface during nano-indentation. Several indentation simulations are executed with different interatomic potentials and different indenter orientations. A surface structure is identified that forms consistently regardless of these variables. This structure is found to affect several atomic layers of the sample. The implications of this effect on the onset of plasticity are discussed. Finally, the implementation of an elastic/plastic continuum contact solution for use in mesoscale molecular dynamics simulations of solid spheres is discussed. The contact model improves on previous models for the forces response of colliding spheres by accounting for a plastic regime after the point of yield. The specifics of the model and its implementation are given in detail. Overall, the dissertation presents insights into basic plastic deformation phenomena using a combination of experiment and theory. Despite the limitations of atomistic techniques, current computational power allows meaningful comparison with experiments.
    URI
    http://hdl.handle.net/10919/78704
    Collections
    • Doctoral Dissertations [15921]

    If you believe that any material in VTechWorks should be removed, please see our policy and procedure for Requesting that Material be Amended or Removed. All takedown requests will be promptly acknowledged and investigated.

    Virginia Tech | University Libraries | Contact Us
     

     

    VTechWorks

    AboutPoliciesHelp

    Browse

    All of VTechWorksCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    My Account

    Log inRegister

    Statistics

    View Usage Statistics

    If you believe that any material in VTechWorks should be removed, please see our policy and procedure for Requesting that Material be Amended or Removed. All takedown requests will be promptly acknowledged and investigated.

    Virginia Tech | University Libraries | Contact Us