Date of Award

Fall 2018

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Marko Knezevic

Second Advisor

Igor Tsukrov

Third Advisor

Brad Kinsey

Abstract

Large number of metallic parts is produced from the raw materials by a set of mechanical shaping and heating operations. Considering the need for metallic components in the modern industry, the field of thermo-mechanical processing of metallic materials is of immense importance. Even modest improvements of the existing thermo-mechanical processes could potentially result in great savings of time, recourses and energy. Finite element modeling of the forming and heating operations introduced in the past decades has allowed for the optimization of the thermo-mechanical processes and has thus resulted in significant advancements. However, due to the limitations of the presently used constitutive models, certain aspects of the process and effects of the process parameters on the component properties cannot be simulated accurately. Work presented in this dissertation is a contribution to the development of a physics-based crystal plasticity model capable of accurately simulating both the mechanical shaping and heating portions of the process and their effect on the microstructure of the component. The well-established visco-plastic self-consistent polycrystal plasticity (VPSC) model is advanced in several aspects in an effort to develop a coupled deformation-recrystallization model. First, different numerical implementation of the VPSC constitutive model into the finite element framework is developed. In addition, two methods for the accurate representation of the material rate sensitivity within the finite element framework are proposed. The proposed models are verified on Taylor impact tests of Zr and Ta cylinders. Next, an algorithm for statistical description of intragranular fluctuations of crystallographic orientation is developed. The effects of the fluctuations of crystallographic orientation within the grains on the fluctuations of stress and rotation rates are considered as well. The developed model is applied to compression and plane strain compression of fcc material and verified by direct comparison with experimental measurements and full-field predictions. Finally, a physics-based recrystallization model coupled with the developed VPSC model capable of predicting intragranular crystallographic orientation fluctuations is proposed. The coupled deformation-recrystallization model is applied to the recrystallization of fcc and bcc materials and reasonable agreement is observed. Combination of different models proposed in this dissertation allows for the simulation of both shaping and heating portions of the thermo-mechanical process.

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