Multiscale modelling of MgO plasticity
Abstract
Among the major phases of the deep mantle, (Mg,Fe)O is of special interest since it is the only mineral which is accessible under surface conditions (allowing the model to be validated from experimental data). The present work will focus on plastic deformation of MgO taken as a proxy for ferropericlase. We propose the first multiscale model of plasticity of pure MgO single crystals which links the electronic properties to the rheology. The core structure of the rate-controlling 1/2<110> screw dislocations has been modelled with the Peierls Nabarro Galerkin method. This model relies on gamma-surfaces calculated ab initio for the {110}, {100} and {111} planes. The <110> screw dislocation spread mostly in the {110} planes. Its Peierls frictions are 150 MPa and 1.6 GPa for glide in {110} and {100} respectively. The kink-pair theory is applied to model thermal activation of dislocation glide over the Peierls barrier below the athermal temperature Ta and to built a velocity law in this regime. The critical resolved shear stresses are deduced below Ta from the Orowan law. Above Ta, the athermal stress is obtained from discrete dislocation dynamics simulations to account for dislocation-dislocation interactions. This model is found to reproduce satisfactorily the critical resolved shear stresses observed experimentally, provided the contribution of impurities (unavoidable in experiments) is subtracted.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMMR51A1899C
- Keywords:
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- 3902 MINERAL PHYSICS / Creep and deformation;
- 3904 MINERAL PHYSICS / Defects