Çekme ve darbe yükleri altındaki tek ve çok kristalli yüksek manganlı östenitik çeliklerde mikro-deformasyon mekanizmalarının deformasyon davranışındaki rollerinin modellenmesi

The aim of the work presented herein is to model the roles of micro-deformation mechanisms on the deformation response of high-manganese austenitic steel single and polycrystals deformed under tensile and impact loading. The first part of this study uncovers the individual roles of twinning and slip-twin interactions on the deformation response of twinning induced plasticity steels (TWIP) utilizing a crystal plasticity approach. The plastic deformation mechanisms active in and the strain hardening behaviors of [100], [110] and [216] oriented single crystalline and polycrystalline TWIP samples were investigated at room temperature utilizing combined experimental and numerical methods. Transmission electron microscopy results revealed that very fine twins with a low contribution to the overall twin volume fraction vary in length scales, and interact with each other and dislocations, enhancing the work hardening capacity of the material. In order to predict the corresponding macroscopic deformation response, a novel strain hardening law was proposed, which accounts for the important contributions of slip-twin and grain boundary - dislocation interactions on the strain hardening response. The proposed hardening scheme was implemented into visco-plastic self-consistent crystal plasticity algorithm, and the model successfully predicted the macroscopic deformation response. More importantly, the current findings shed light onto the individual contributions of twinning and slip-twin interactions on the overall work hardening capacity of TWIP steels. In the second part, a multi-scale modeling approach was applied to predict the impact response of strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE) analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial tensile loading. The equivalent stress – equivalent strain response was then incorporated into the FE model for the sake of a more representative hardening rule under impact loading. The current results demonstrate that reliable predictions can be obtained by proper coupling of crystal plasticity and FE analysis even if the experimental flow rule of the material is acquired under uniaxial loading and at moderate strain rates that are significantly slower than those attained during impact loading. Furthermore, the current findings also demonstrate the need for an experiment-based multiscale modeling approach for the sake of reliable predictions of the impact response.