DOI

10.17077/etd.0z10ic54

Document Type

Dissertation

Date of Degree

Spring 2018

Degree Name

PhD (Doctor of Philosophy)

Degree In

Mechanical Engineering

First Advisor

Ding, Hongtao

First Committee Member

Beckermann, Christoph

Second Committee Member

Bhatti, Asghar

Third Committee Member

Choi, Kyung K

Fourth Committee Member

Udaykumar, H S

Abstract

The objective of the research presented in this thesis has been to develop a physics-based dislocation density-based numerical framework to simulate microstructure evolution in severe plastic deformation (SPD) manufacturing processes for different materials. Different mechanisms of microstructure evolution in SPD manufacturing processes were investigated and summarized for different materials under dynamic or high strain rates over a wide temperature range. Thorough literature reviews were performed to clarify discrepancies of the mechanism responsible for the formation of nanocrystalline structure in the machined surface layer under both low-temperature and high-temperature conditions.

Under this framework, metallo-thermo-mechanically (MTM) coupled finite element (FE) models were developed to predict the microstructure evolution during different SPD manufacturing processes. Different material flow stress responses were modeled subject to responsible plastic deformation mechanisms. These MTM coupled FE models successfully captured the microstructure evolution process for various materials subjected to multiple mechanisms.

Cellular automaton models were developed for SPD manufacturing processes under intermediate to high strain rates for the first time to simulate the microstructure evolution subjected to discontinuous dynamic recrystallization and thermally driven grain growth. The cellular automaton simulations revealed that the recrystallization process usually cannot be completed by the end of the plastic deformation under intermediate to high strain rates. The completion of the recrystallization process during the cooling stage after the plastic deformation process was modeled for the first time for SPD manufacturing processes at elevated temperatures.

Keywords

Cellular automaton, dislocation density, Dynamic recrystallization, finite element model, Microstructure, Severe plastic deformation

Pages

xv, 191 pages

Bibliography

Includes bibliographical references (pages 172-191).

Copyright

Copyright © 2018 Ninggang Shen

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