[SY-N6] Modelling metals, alloys and cement paste across length and time scales
Invited
Fundamentally, structural materials are bound by atomistic cohesive interactions, while our societies use these to design systems at scales of meters—or more. Likewise, the material’s microstructural evolution takes place on scales as short as nanoseconds—e.g. diffusion of radiation-induced defects clusters in metallic alloys—all the way up to decades—e.g. creep of concrete under load.
This presentation will focus on applying multi-scale methods to address these challenges for two classes of systems: (1) metals and alloys under irradiation, and (2) calcium silicate hydrates (C-S-H), the main binding phase of cement paste.
In metals and alloys, the kinetics of collision cascade induced defects was modelled using adaptive kinetic Monte Carlo. Namely, the kinetic Activation Relaxation Technique —a self-learning, fully atomistic algorithm able to handle off-lattice defects and handle long-range elastic interactions—was used to capture the time-evolution of cascade debris after neutron or ion irradiation. Furthermore, a detailed investigation of point-defect diffusion in NixFe(1-x) concentrated alloys revealed a non-monotonic dependence of diffusion coefficients as a function of Fe concentration. This was explained by coupling percolation effects with the composition dependence of point-defect vacancy migration energies.
In C-S-H, the adsorption of alkali ions—Na, K, and Cs—was studied, in the context of the alkali-silica reaction and spent fuel storage. By applying molecular dynamics, semi-grand canonical Monte Carlo, and the Activation Relaxation Technique nouveau, adsorption of alkali ions in the hydrated layer of C-S-H was characterized. The effect of alkali uptake on mesoscale mechanical properties was calculated using a coarse-grained model of C-S-H. While alkali uptake leads to significant expansion of individual C-S-H grains, it leads to modest—less than 5 MPa—mesoscopic expansive pressure, well within the elastic regime of concrete.
This presentation will focus on applying multi-scale methods to address these challenges for two classes of systems: (1) metals and alloys under irradiation, and (2) calcium silicate hydrates (C-S-H), the main binding phase of cement paste.
In metals and alloys, the kinetics of collision cascade induced defects was modelled using adaptive kinetic Monte Carlo. Namely, the kinetic Activation Relaxation Technique —a self-learning, fully atomistic algorithm able to handle off-lattice defects and handle long-range elastic interactions—was used to capture the time-evolution of cascade debris after neutron or ion irradiation. Furthermore, a detailed investigation of point-defect diffusion in NixFe(1-x) concentrated alloys revealed a non-monotonic dependence of diffusion coefficients as a function of Fe concentration. This was explained by coupling percolation effects with the composition dependence of point-defect vacancy migration energies.
In C-S-H, the adsorption of alkali ions—Na, K, and Cs—was studied, in the context of the alkali-silica reaction and spent fuel storage. By applying molecular dynamics, semi-grand canonical Monte Carlo, and the Activation Relaxation Technique nouveau, adsorption of alkali ions in the hydrated layer of C-S-H was characterized. The effect of alkali uptake on mesoscale mechanical properties was calculated using a coarse-grained model of C-S-H. While alkali uptake leads to significant expansion of individual C-S-H grains, it leads to modest—less than 5 MPa—mesoscopic expansive pressure, well within the elastic regime of concrete.