Adiabatic Shear banding in Titanium 15-3-3-3 Alloy
Akbari, Azin (2013)
Master's Degree Programme in Materials Science
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Shear stresses are a common reason for failure in many industrial applications. Localized shear deformations in certain materials can lead to the formation of adiabatic shear bands. Titanium alloys in particular have proven to be good candidates for the formation of the adiabatic shear bands. For this reason, this study focuses on the shear behavior of Ti 15-3-3-3 alloy, and especially the shear localizations during deformation at various strain rates. Shear strains are localized into a narrow region in the hat-shaped specimens due to the geometry of the specimen. Therefore, in this study, the mechanical behavior of Ti-15-3-3-3 alloy was studied using the Split Hopkinson Pressure Bar (at high strain rates) and servo-hydraulic materials testing machine (at lower strain rates) using the hat-shape specimens. Stopper rings were used to limit the amount of deformation and consequently the amount of applied strain to a predetermined value. The microstructures of the adiabatic shear bands were studied using optical and scanning electron microscopy. The widths of the shear bands were measured from the micrographs of the samples with different amounts of deformation. In some samples, also individual slip bands appeared clearly outside the primary shear zone. These individual slip bands were neglected in the calculations of stress vs. strain curves, and therefore the deformation was assumed to be limited to the primary shear band area only. Finally it was concluded that the shear band width is independent of the amount of strain in the high strain rate tests. This constant value was used in the calculations of shear strain and strain rate. The shear stress and shear strain for each test were calculated and the obtained stress-strain curves were analyzed. Different mechanical behavior was observed in the high strain rate test results compared to the results obtained at low strain rates. At high strain rates the effect of strain hardening is significantly weaker than the thermal softening in the primary shear band, leading to a strongly localized deformation and constant shear band width.