Large Scale DD Simulation Results for Crystal Plasticity Parameters in Fe-Cr And Fe-Ni Systems

Abstract

SUMMARYThe development of viable nuclear energy source depends on ensuring structural materials integrity. Structural materials in nuclear reactors will operate in harsh radiation conditions coupled with high level hydrogen and helium production, as well as formation of high density of point defects and defect clusters, and thus will experience severe degradation of mechanical properties. Therefore, the main objective of this work is to develop a capability that predicts aging behavior and in-service lifetime of nuclear reactor components and, thus provide an instrumental tool for tailoring materials design and development for application in future nuclear reactor technologies. Towards this end goal, the long term effort is to develop a physics-based multiscale modeling hierarchy, validated and verified, to address outstanding questions regarding the effects of irradiation on materials microstructure and mechanical properties during extended service in the fission and fusion environments. The focus of the current investigation is on modern steels for use in nuclear reactors including high strength ferritic-martensitic steels (Fe-Cr-Ni alloys).The effort is to develop a predictive capability for the influence of irradiation on mechanical behavior. Irradiation hardening is related to structural information crossing different length scales, such as composition, dislocation, and crystal orientation distribution. To predict effective hardening, the influence factors along different length scales should be considered. Therefore, a hierarchical upscaling methodology is implemented in this work in which relevant information is passed between models at three scales, namely, from molecular dynamics to dislocation dynamics to dislocation-based crystal plasticity. The molecular dynamics (MD) was used to predict the dislocation mobility in body centered cubic (bcc) Fe and its Ni and Cr alloys. The results are then passed on to dislocation dynamics to predict the critical resolved shear stress (CRSS) from the evolution of local dislocation and defects.In this report the focus is on the results obtained from large scale dislocation dynamics simulations. The effects of defect density and materials structure were investigated while new evolution laws were proposed. These results will form the bases for the development of evolution and hardening laws for a dislocation-based crystal plasticity framework. The hierarchical upscaling method being developed in this project can provide a guidance tool to evaluate performance of structural materials for nextgeneration nuclear reactors. Combined with other tools developed in the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program, the models developed will have more impact in improving the reliability of current reactors and affordability of new reactors.

Gradient Plasticity Model and its Implementation into MARMOT

“…Phenomenological theories of strain gradient plasticity were proposed by Fleck, Hutchinson and other front runners in the past decades, as summarized in several excellent reviews (Evans and Hutchinson, 2009;Fleck and Hutchinson, 1997;Fleck et al, 1994). In our previous studies (Li et al, in preparation;Zbib et al, 2012), we have developed a multi--scale modeling framework to simulate the mechanical deformation behavior of nuclear structural materials including bcc iron alloys. The work flow of this multi--scale framework starts Gradient Plasticity and its Implementation into MARMOT 2 Aug 2013 from molecular dynamics (MD), to discrete dislocation dynamic (DDD), to continuum dislocation dynamics (CDD), to crystal plasticity (CP) model and FEM.…”