THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Wednesday, April 28, 2021

1:00 PM

via

Blue Jeans Video Conferencing

https://bluejeans.com/720842150

will be held the

DISSERTATION DEFENSE

for

Syed Saad Javaid

"Deformation and Damage Evolution in Thin Metal Sheets using Incremental Strain Field Mining"

Committee Members:

Prof. Christopher Muhlstein, Advisor, MSE

Prof. Naresh Thadhani, MSE

Prof. Richard Neu, ME/MSE

Prof. Preet Singh, MSE

Prof. Olivier Pierron, ME

Abstract:

Deformation and crack behavior is difficult to characterize in ductile metals at sub-millimeter thicknesses using conventional fracture mechanics approaches. This is because of the challenges posed by large scale plasticity, uncontained yielding and instabilities like diffuse and transverse necking. We observe quasi-static steady-state process zones under fully-plastic crack tip conditions that are facilitated by plane stress conditions associated with the thin sheet form factor. In this work, we utilize an incremental strain framework based on high resolution, full field digital image correlation and tracking (DICT) to examine process zone evolution during steady-state conditions. We identify the existence of continually evolving zones of active plasticity (ZAP) which embed different types of zones including the fracture process zone (FPZ) within it. We quantify the shape and extent of these stationary and moving process zones and provide insights on the factors that affect them. We probe scaling and coupling relationships of different types of zones in the steady-state regime. We also show distinct differences in zone evolution for monotonic vs cycle loading conditions. We investigate the structure-property-processing paradigm by characterizing zones for Al, Cu, and Ti in multiple specimen orientations and study how engineering conditions zone engineering such as hydrogen charging or change in temperature to induce different mechanisms affect the zones. We tie the observed zone extents in the incremental framework to strain ranges for key deformation features such as diffuse/localized necking and failure. This work provides an incremental strain framework which is applied across materials, loading conditions to provide consistent scaling relationships. We also provide key insights into the zone evolution in the steady-state regime and offer important extent/path information that can be used to predict deformation behavior in this class of materials.