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dc.contributor.advisorThadhani, Naresh N.
dc.contributor.authorGonzales, Manny
dc.date.accessioned2016-01-07T17:25:48Z
dc.date.available2016-01-07T17:25:48Z
dc.date.created2015-12
dc.date.issued2015-11-16
dc.date.submittedDecember 2015
dc.identifier.urihttp://hdl.handle.net/1853/54393
dc.description.abstractThis work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved. A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.publisherGeorgia Institute of Technology
dc.subjectEnergetic materials
dc.subjectShock physics
dc.subjectShock compression
dc.subjectPowders
dc.subjectTitanium diboride
dc.subjectAluminum
dc.subjectHigh-strain-rate impact
dc.subjectPlate impact
dc.subjectPVDF gauges
dc.subjectVISAR
dc.subjectMeso-scale simulation
dc.subjectMicrostructures
dc.subjectModeling
dc.subjectReactive materials
dc.subjectUniaxial stress loading
dc.subjectUniaxial strain loading
dc.subjectTiB₂
dc.titleThe mechanochemistry in heterogeneous reactive powder mixtures under high-strain-rate loading and shock compression
dc.typeDissertation
dc.description.degreePh.D.
dc.contributor.departmentMaterials Science and Engineering
thesis.degree.levelDoctoral
dc.contributor.committeeMemberGokhale, Arun M.
dc.contributor.committeeMemberSanders, Thomas H.
dc.contributor.committeeMemberMcDowell, David L.
dc.contributor.committeeMemberJacobs, Laurence J.
dc.date.updated2016-01-07T17:25:48Z


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