UCLA

Microstructure evolution of structural materials under fission/fusion irradiaiton con- ditions lead to significant degradation to their mechanical properties. These effects include an increase in yield stress, plastic localization and accelerated creep rate, etc. Besides, damaged materials inevitably exposing to hydrogen or its isotopes would result in embrittlement and safety problem. Regarding these problems, we in this thesis developed three types of numerical models and attempted to solve each of those. First, a previously developed kMC algorithm based 0-dimentional mean field rate theory model, the stochastic cluster dynamics (SCD), is extended to have 1- dimentional spatial resolution (SRSCD). The SRSCD method is then used to sim- ulate: (1) Zr-hydride nucleation and growth processes under dynamic oxide layer growth conditions; (2) Hydrogen retention in heavy ion irrdiated tungsten. Second, the SCD method is coupled with a general implicit crystal plasticity (CP) formulation (CP/SCD) using a bidirectional variable swap scheme. The CP/SCD model is capable of capturing concurrent irradiation/straining process in materials and is applied to study (1) Irradiation hardening of self-ion irradiated tungsten under tensile loading conditions; (2) Creep and swelling effects of DEMO neutron irradiated iron. Finally, a stochastic solver based on residence time algorithm is developed for solving a typical explicit crystal plasticity (SCP) procedure. The stochasitc nature of SCP is seen to break the symmetry of dislocation slip, which shows potential in studying plastic localization problems.