SUBJECT: Ph.D. Proposal Presentation
BY: Cameron Sobie
TIME: Friday, July 31, 2015, 5:00 p.m.
TITLE: Prediction of Irradiation Hardening in Metals
COMMITTEE: Dr. Laurent Capolungo, Chair (ME)
Dr. David McDowell (ME)
Dr. Ting Zhu (ME)
Dr. Tom Sanders (MSE)
Dr. Enrique Martinez (LANL)


This thesis aims to investigate the evolution of mechanical properties in irradiated metals from a micro-scale dislocation perspective. Nuclear reactions produce high energy particles capable of creating lattice defects in crystalline structures, and such defects act as obstacles to dislocation motion. To elucidate their effect on macroscopic material properties, several studies across a wide range of length and time scales are proposed. First, a discrete dislocation dynamics code is extended to nanoscale microstructures with dislocation-irradiation defect interactions. Next, the predictive capabilities of several athermal constitutive equations modelling material hardening starting from single dislocation-obstacle interactions are investigated in the case of irradiation-induced defects in alpha-iron using an atomistic-informed dislocation dynamics simulation. The increase in flow stress caused by the presence of voids and self-interstitial atom loops is calculated and compared to the models' predictions and the most accurate model is determined. A superposition principle for the hardening contributions of different obstacles is developed to enable the validated laws to be applied to materials containing both defect types. Extending these results beyond athermal behaviour to the broad temperature range observed across a nuclear pressure vessel requires a dramatic shift in approach. Harmonic transition state theory is a cornerstone of coarse-graining and provides a methodology to incorporate thermally activated dislocation processes. A new technique for computationally efficient activation energy calculations for dislocation-obstacle bypass is proposed using a novel technique coupling discrete dislocation dynamics to the nudged elastic band method. First, the energy landscape of a dislocation bypassing a single self interstitial loop is characterised before extending to large scale simulations with the goal of directly predicting the creep rate for glide-mediated creep.