Microstructural evolution of adiabatic shear bands in steel by impact

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dc.contributor.authorBoakye-Yiadom, Solomon
dc.contributor.examiningcommitteePolyzois, Dimos (Civil Engineering) Ojo, Olanrewaju (Mechanical Engineering) Glinka, Gregory (University of Waterloo)en_US
dc.contributor.supervisorBassim, Nabil (Mechanical Engineering)en_US
dc.date.accessioned2014-10-16T14:20:19Z
dc.date.available2014-10-16T14:20:19Z
dc.date.issued2014en_US
dc.degree.disciplineMechanical Engineeringen_US
dc.degree.levelDoctor of Philosophy (Ph.D.)en_US
dc.description.abstractThis research, is initiated to systematically study the microstructure of AISI 4340 steel prior to impact, after impact and after post-impact annealing to determine the effect of the pre-deformation microstructure on the nucleation and initiation of ASBs, and the mechanism of evolution of ASBs during impact. This study used state-of-the-art microstructural characterization techniques such as the FIB and STEM/HRTEM to reveal that initial microstructural inhomogeneity produces nucleation sites for the initiation of ASBs during impact. It was observed that double misfit interfaces and boundary layers, formed around precipitated carbides (interface between reinforcements and matrix), increased the volume fraction of dislocation sources within the pre-impact specimens. It is demonstrated that the intersection of an activated dislocation source with the direction of maximum shear (regions of stress concentrations) within the specimens during impact, is a necessary condition for the points of intersection to act as possible sites for the nucleation and initiation of ASB depending on the rate of dislocation generation, local strain and strain rate. In addition, the structure that evolves after strain localization starts out with elongation of the grains in the shear direction with the initiation of random and transverse dislocation boundaries along the elongated grains. The elongated grains break along the initiated dislocation boundaries as strain/strain rate increases resulting in the creation of smaller elongated-broken grains and nanograins. Boundary refinement of the broken grains occurring through grain rotation and adiabatic heating results in the evolution of refined grains, subgrains and nanograins. The presence of elongated grains, broken grains, refined grains, subgrains and nanograins within the evolved shear band structures demonstrate that the local deformation is dependent on the imposed local strain and strain rate and that these mechanisms occur concurrently during impact. The results obtained, which are specific to the behavior of BCC ferritic Pearlitic hardenable steels, lead to the conclusion that the evolution of ASBs is a simultaneous layering of microstructures initially driven by dislocations which produce the final structures observed in the shear bands at the end of passage of the stress wave.en_US
dc.description.noteFebruary 2015en_US
dc.identifier.citationS. Boakye-Yiadom And M. N. Bassim, Effect Of Prior Heat Treatment On The Dynamic Impact Behavior Of 4340 Steel And Formation Of Adiabatic Shear Bands, Materials Science And Engineering A (2011) 8700-8708en_US
dc.identifier.citationS. Boakye-Yiadom And M. N. Bassim, Effect Of Heat Treatment On Stability Of Impact-Induced Adiabatic Shear Bands In 4340 Steel, Materials Science And Engineering A 546 (2012) 223-232en_US
dc.identifier.citationS. Boakye-Yiadom, N. Bassim And A. K. Khan, Microscopical Study Of The Formation Of Adiabatic Shear Bands In 4340 Steel During Dynamic Loading, Philosophical Magazine 93 (2013) 4544-4568en_US
dc.identifier.citationS. Boakye-Yiadom, A. K. Khan And N. Bassim, A Systematic Study Of Grain Refinement During Impact Of 4340 Steel, Materials Science And Engineering A 605 (2014) 270–285en_US
dc.identifier.citationS. Boakye-Yiadom, A. K. Khan And N. Bassim, Deformation Mapping and the Role of Carbides on the Microstructure and Properties of Evolved Adiabatic Shear Bands, Metallurgical And Materials Transaction A 45 (2014) 5379-5396en_US
dc.identifier.citationS. Boakye-Yiadom, A. K. Khan And N. Bassim, Effect of Pre-impact Microstructure on the nucleation and initiation of Adiabatic Shear Bands (ASBs) During Impact, Materials Science And Engineering A (2014) 373-394en_US
dc.identifier.urihttp://hdl.handle.net/1993/24095
dc.language.isoengen_US
dc.publisherMaterials Science And Engineering Aen_US
dc.publisherMaterials Science And Engineering Aen_US
dc.publisherPhilosophical Magazineen_US
dc.publisherMaterials Science And Engineering Aen_US
dc.publisherMetallurgical And Materials Transaction Aen_US
dc.publisherMaterials Science And Engineering Aen_US
dc.rightsopen accessen_US
dc.subjectMicroscopyen_US
dc.subjectDislocationsen_US
dc.subjectAdiabatic Shear Bandsen_US
dc.subjectX-ray Diffractionen_US
dc.subjectImpacten_US
dc.subjectFocused Ion Beamen_US
dc.titleMicrostructural evolution of adiabatic shear bands in steel by impacten_US
dc.typedoctoral thesisen_US
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