[SY-F11] Multiscale modelling of the effective viscoplastic behavior of constituents of the mantle transition zone (Mg2SiO4 wadsleyite and ringwoodite): bridging atomic and polycrystal scales
The Earth mantle transition zone (an envelope of the Earth’s interior between 410 and 660 km depth) is constituted by more than half from wadsleyite and ringwoodite. Waldseyite is present up to 525km depth, whereas ringwoodite appears below. In the transition zone, pressure ranges from 14 GPa to 24GPa, and temperature lies between 1880°K and 1900°K. Estimation of the viscoplastic behavior of these constituents, and the link with their microstructure (crystallographic texture), is crucial to better understand the structure of large scale convection cells in the mantle responsible for plate tectonic.
In this work, the viscoplastic behavior of wadsleyite and ringwoodite polycrystalline aggregates (cm scale) is obtained by bridging several scale transition models, starting from very fine scale (nm) of the dislocation core structure. This presentation will emphasize the grain-polycrystal scale transition.
Deformation resulting from thermally activated dislocation glide has been modeled in wadsleyite and ringwoodite at high pressures, for a wide range of temperatures, and under laboratory and in situ (i.e. mantle) strain-rates conditions. The model relies on the structure and kink pairs nucleation enthalpies of the rate controlling screw dislocations which have been modeled using the Peierls-Nabarro-Galerkin method and an elastic interaction model. Corresponding single slip critical resolved shear stresses (CRSS), and associated constitutive equations have been deduced from Orowan’s equation in order to describe the average viscoplastic behavior at the grain scale, for all available slip systems.
These data are then implemented in two grain-polycrystal scale transition models, a statistical one (Second-Order Viscoplatic Self-Consistent scheme) allowing rapid evaluation of the effective viscosity of the polycrystalline aggregates, and a full-field method (FFT based method) allowing investigating many inter- and intra-granular features such as stress and strain localization in a typical microstructure, heterogeneous activation of slip systems, etc. Calculations have been performed for pressure, temperature, and strain-rates conditions corresponding to laboratory and in situ conditions. The obtained effective behavior is in very good match with available experimental data.
In this work, the viscoplastic behavior of wadsleyite and ringwoodite polycrystalline aggregates (cm scale) is obtained by bridging several scale transition models, starting from very fine scale (nm) of the dislocation core structure. This presentation will emphasize the grain-polycrystal scale transition.
Deformation resulting from thermally activated dislocation glide has been modeled in wadsleyite and ringwoodite at high pressures, for a wide range of temperatures, and under laboratory and in situ (i.e. mantle) strain-rates conditions. The model relies on the structure and kink pairs nucleation enthalpies of the rate controlling screw dislocations which have been modeled using the Peierls-Nabarro-Galerkin method and an elastic interaction model. Corresponding single slip critical resolved shear stresses (CRSS), and associated constitutive equations have been deduced from Orowan’s equation in order to describe the average viscoplastic behavior at the grain scale, for all available slip systems.
These data are then implemented in two grain-polycrystal scale transition models, a statistical one (Second-Order Viscoplatic Self-Consistent scheme) allowing rapid evaluation of the effective viscosity of the polycrystalline aggregates, and a full-field method (FFT based method) allowing investigating many inter- and intra-granular features such as stress and strain localization in a typical microstructure, heterogeneous activation of slip systems, etc. Calculations have been performed for pressure, temperature, and strain-rates conditions corresponding to laboratory and in situ conditions. The obtained effective behavior is in very good match with available experimental data.