We are pleased to announce that the Scientific Council of IPPT PAN has awarded MSc Eng. Saketh Virupakshi the degree of Doctor of Engineering and Technology in Mechanical Engineering with a distinction of his doctoral dissertation. The doctoral dissertation is titled: „Micromechanical modelling of voided FCC and HCP polycrystals in inelastic regime”.
Fig.1., from left: dr Saketh Virupakshi, prof. Katarzyna Kowalczyk-Gajewska, Priyanka Ganji.
In this thesis, numerical analyses and a micromechanical approach were employed to unravel the mechanisms governing the ductile failure and its impact on the macroscopic response of porous single and polycrystals with FCC and HCP lattice symmetries. In the performed analyses relevant deformation mechanisms at the local level were considered, and appropriate micro-macro transition schemes were applied. A rate-dependent crystal plasticity constitutive model was employed, incorporating slip and twin mechanisms. In the model the evolution of the critical resolved shear stress (CRSS), influenced by the interaction between various slip and twin systems, and crystal reorientation scheme due to twinning were accounted for. Detailed results from numerical simulations on single and polycrystal unit cell models, conducted using the crystal plasticity finite element method (CPFEM), are presented, analyzing how plastic anisotropy, stress state, and boundary conditions affect void growth, coalescence, and collapse in porous FCC and HCP single and polycrystals.
The work also explores the possibility of describing the macroscopic responses of porous crystals and polycrystals through micromechanical mean field models. The formulated mean field model uses the additive Mori-Tanaka scheme for porous single crystals and a three-scale model based on the additive self-consistent scheme for porous polycrystals. They are both validated against full-field numerical analyses. Additionally, using the proposed micromechanical model, a Gurson-Tvergaard-Needleman-like yield criterion for porous crystals was formulated, and its predictions were compared with existing models and validated with respect to numerical unit cell results. This newly proposed yield condition is well suited for the implementation into the finite element framework, following similar implementations by Ling et al. (2016) to predict damage in porous crystals. The results demonstrate that the numerical analyses and micromechanical approach are effective tools for understanding the relation between material microstructure, including the crystal lattice symmetry, and the developed scenarios of void growth and related changes in macroscopic response of metallic materials.
