Multiscale modeling of the mechanical behavior of structural materials in nuclear energy systems

Nasr M. Ghoniem

The multiscale modeling methodology is now a cornerstone in world programs aimed at designing radiation-resistant structural materials in the harsh environments encountered in Nuclear Energy Systems. The strategy is based on a hierarchy of materials models connected sequentially at appropriate interfaces of length and time scales, and utilizes concepts of "separation of scales," as appropriate. Basic defect properties, such as the energetics of point defect formation and migration, and lattice resistance to dislocation slip, are determined by ab initio methods, and are parameterized and utilized in upper length-scale methods. Molecular dynamics simulations reveal specific outcomes of reactions between defects (e.g. dislocations and point defect clusters), or the structure of displacement damage caused by energetic particle collisions. The collective behavior of mobile point defect cluster ensembles is determined by Kinetic Monte Carlo simulations, where the degrees of freedom are reduced to those pertinent to the defects themselves and not all participating atoms. Plastic deformation and fracture phenomena at the micron length scale are fundamentally determined through 3-dimensional Dislocation dynamics simulations. In this talk, we outline this strategy and show how it is used to understand and design radiation-resistant materials. Examples of modeling the low-temperature embrittlement and fracture of ferritic/martensitic steels and the shift in the Ductile-to-Brittle-Transition-Temperature (DBTT) by neutron irradiation will be given. At the component length scale, we discuss the development of microstructure-based constitutive models that can be incorporated into crystal plasticity. A global-local approach for coupling large-scale global Finite Element Modeling (FEM) to crystal plasticity analysis of local deformation at critical regions of fusion structures will also be shown.

This work is supported by the U.S. Department of Energy, Office of Fusion Energy Science, and by the UCLA NERI Grant DE-FC07-06ID14748