SUBJECT: Ph.D. Dissertation Defense
   
BY: Seyed Ali Tabei
   
TIME: Monday, March 9, 2015, 8:00 a.m.
   
PLACE: MARC Building, 201
   
TITLE: Modeling of Microstructural Evolutions in Machining of Dual Phase Alloys
   
COMMITTEE: Dr. Steven Y. Liang, Co-Chair (ME)
Dr. Hamid Garmestani, Co-Chair (MSE)
Dr. Antonia Antoniou (ME)
Dr.Karl I. Jacob (ME)
Dr. Guillermo Goldsztein (MATH)
Dr. Sad Ahzi (MSE)
 

SUMMARY

Depending on the material system and machining conditions, the localized strain, strain rate and temperature fields induced to the material during the process can be intense. Therefore, a wide variety of localized microstructural evolutions are likely to occur below the machined surface. These microstructural evolutions take place at various scales. First of all, due to the severe plastic deformation below the machined surface, the crystallographic orientation can change dramatically. In addition, if the levels of induced temperature and strain are high enough, recrystallization may occur, new grains may form and subsequently grow. Additionally, contingent upon the duration of the machining process, partial grain growth might also happen. Last but not least, if the material is consisted of more than one phase, the microstructural characteristics of secondary phases will also evolve. The ultimate result of all the aforementioned evolutions is a possible remarkable change in the mechanical and thermal (and almost all the other) properties of the material, which consequently affects the response of the material during service. A comprehensive modeling framework that reliably captures all the aspects of the above microstructural evolutions in machining is absent in the open literature. This work constructs a concrete all-inclusive modeling toolset to follow the mentioned phenomena for aluminum alloy 7075. The modeling outcomes are verified by experimental results at various steps to assure reliability. Finite element analysis was applied to obtain the stress, temperature, strain and strain rate fields developed in the material during machining at different parameters. Kinetic-based models are exploited to determine the possible recrystallization or grain growth. A viscoplastic self-consistent crystal plasticity model is utilized to investigate texture evolutions below the machined surface. Also for multi-phase materials, the first steps in developing a totally new constitutive model to yield the extent of the possible refinement in second phase precipitates are taken. The main goal of the work is to link the above-mentioned microstructural evolutions to process parameters of machining by constructing a microstructure hull. Therefore, prediction of microstructural changes as a result of process parameters becomes possible, which has significant industrial potential. Additionally, such a direct and complete linkage between machining and microstructure is completely new to the scientific community in manufacturing and design fields.