{"65756":{"#nid":"65756","#data":{"type":"event","title":"MSE Ph.D. Defense - Garritt Tucker","body":[{"value":"\u003Cp\u003E\u003Cstrong\u003ETitle\u003C\/strong\u003E: ATOMISTIC SIMULATIONS OF DEFECT NUCLEATION AND FREE\nVOLUME IN NANOCRYSTALLINE MATERIALS\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ESummary\u003C\/strong\u003E: In this research, atomistic simulations are employed to\ninvestigate defect nucleation and free volume of grain boundaries and\nnanocrystalline materials. Nanocrystalline materials are of particular interest\ndue to their improved mechanical properties and alternative strain\naccommodation processes at the nanoscale. These processes, or deformation\nmechanisms, within nanocrystalline materials are strongly dictated by the\nlarger volume fraction of grain boundaries and interfaces due to smaller\naverage grain sizes. The behavior of grain boundaries within nanocrystalline\nmaterials is still largely unknown. One reason is that experimental\ninvestigation at this scale is often difficult, time consuming, expensive, or\nimpossible with current resources. Atomistic simulations have shown the\npotential to probe fundamental behavior at these length scales and provide\nvital insight into material mechanisms. Therefore, we utilize atomistic\nsimulations to explore structure-property relationships of face-centered-cubic\n(fcc) grain boundaries, and investigate the deformation of nanocrystalline\ncopper as a function of average grain size.\u003C\/p\u003E\n\n\u003Cp\u003EMolecular statics employing an embedded atom method\npotential are utilized in this research to construct fcc bicrystalline grain\nboundary structures.\u003C\/p\u003E\n\n\u003Cp\u003EThe boundaries are then deformed at 10K under uniaxial\ntension and simple shear at a constant strain rate to elucidate the influence\nof interfacial structure on inelastic deformation. An algorithm is also\npresented to compute interfacial free volume in the bicrystalline structures\nand quantitatively track its evolution with imposed strain. Representative\nnon-equilibrium grain boundaries are instantiated using excess free volume as a\nmeasure of the degree of non-equilibrium state, and then deformed to explore\nthe influence of structure on deformation response. It is shown that excess\nfree volume alters interfacial atomic processes critical for dislocation\nnucleation and grain boundary sliding, resulting in lower grain boundary\nstrength.\u003C\/p\u003E\n\n\u003Cp\u003EVolume-averaged kinematic metrics are formulated from\ncontinuum mechanics theory and applied to the results of atomistic simulations\nto provide new insight into atomic deformation and rotation fields. Inelastic\ndeformation mechanisms common to nanocrystalline metals, such as heterogeneous\ndislocation nucleation, grain boundary sliding, and grain boundary migration\nare analyzed with the proposed metrics using bicrystalline grain boundaries.\nThe results indicate that unique deformation fields are associated with each\nmechanism and a sense of the deformation history of the atomic fields are\nprovided through the utilization of neighbor lists from the reference\nconfiguration. Other metrics use current configuration quantities to display\nthe fronts of propagating dislocation networks.\u003C\/p\u003E\n\n\u003Cp\u003EThe kinematic metrics are also leveraged to explore the\ntensile deformation of nanocrystalline copper at 10K. The distribution of\ndifferent strain accommodation mechanisms is estimated and we are able to\npartition the role of competing mechanisms in the the overall strain of the\nnanocrystalline structure as a function of grain size. Grain boundaries are\nobserved to be influential in smaller grained structures, while dislocation\nglide is more influential as grain size increases. Under compression, however,\nthe resolved compressive normal stress on interfaces hinders grain boundary\nplasticity, leading to a tension-compression asymmetry in the strength of\nnanocrystalline copper. The mechanisms responsible for the asymmetry are probed\nwith atomistic simulations and the volume-averaged metrics. Finally, the\nutility of the metrics in capturing non-local nanoscale deformation behavior\nand their potential to inform higher-scaled models is discussed.\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EMSE Ph.D. Defense - Garritt Tucker -- ATOMISTIC SIMULATIONS OF DEFECT NUCLEATION AND FREE\nVOLUME IN NANOCRYSTALLINE MATERIALS\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"MSE Ph.D. Defense - Garritt Tucker"}],"uid":"27388","created_gmt":"2011-04-25 12:25:08","changed_gmt":"2016-10-08 01:54:54","author":"Bill Miller","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2011-05-05T11:00:00-04:00","event_time_end":"2011-05-05T11:00:00-04:00","event_time_end_last":"2011-05-05T11:00:00-04:00","gmt_time_start":"2011-05-05 15:00:00","gmt_time_end":"2011-05-05 15:00:00","gmt_time_end_last":"2011-05-05 15:00:00","rrule":null,"timezone":"America\/New_York"},"extras":[],"groups":[{"id":"1238","name":"School of Materials Science and Engineering"}],"categories":[],"keywords":[{"id":"10802","name":"MSE_Interal_Event"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[],"email":[],"slides":[],"orientation":[],"userdata":""}}}