Ph.D. Program in Mechanical Engineering.Aydıner, C. Can.Alkan, Sertan.Kapan, Enver.2025-04-142025-04-142023Ph.D. Program in Mechanical Engineering. ED 2023 O87 (Thes ESC 2023 S58 PhDhttps://digitalarchive.library.bogazici.edu.tr/handle/123456789/21619Modeling deformation twin nucleation in magnesium has proven to be a challenging task. In particular, the absence of a heterogeneous twin nucleation model which provides accurate energetic descriptions for twin-related structures indicates a need to more deeply understand twin energetics. To address this problem, in a two-part study, molecular dynamics simulations are performed to follow the energetic evolution of {1012} tension twin embryos nucleating from an asymmetrically-tilted grain boundary. The line, surface and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin related structures to the total energy of the twin are evaluated. In the second part of the study, a geometric model is proposed to complement the micromechanical model such that the geometric variables associated with twin related structures are predicted from a few mesoscopic parameters. The results of the geometric model are substituted into the micromechanical model to obtain potential energy surfaces of a wide range of twin configurations. Classical nucleation theory is implemented to predict the nucleation energy barrier for {1012} twinning in Mg. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to be able to offset the energy costs of creating the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be critical considerations when predicting twin nucleation sites in magnesium.Magnesium alloys.Molecular dynamics -- Mathematical models.xix, 110 leaves