Continuous description of a grain boundary in olivine from atomic scale simulations: the role of disclinations

Abstract:

A crossover between atomistic description and continuous representation of grain boundaries in polycrystals is set-up to model the periodic arrays of structural units by using dislocation and disclination dipole arrays along grain boundaries. Continuous modeling of the boundary is built by bottom-up processing, meaning that the strain, rotation, curvature, disclination and dislocation density fields are calculated by using the discrete atomic positions generated by molecular dynamics simulations. Continuous modeling of a 18.9° symmetric tilt boundary in copper [1] is conducted as a benchmark case. Its accuracy is validated by comparison with a similar recent technique [2]. Then, results on the 60.8° Mg₂SiO₄ tilt boundary [3-4] are presented. By linking the atomistic description with continuum mechanics representations, they provide new insights into the structure of the grain boundary.

[1] Fressengeas, C., Taupin, V., Capolungo, L., 2014. Continuous modelling of the structure of symmetric tilt boundaries. Int. J. Solids Struct. 51, 1434–1441.

[2] Zimmerman, J.A., Bammann, D.J., Gao, H., 2009. Deformation gradients for continuum mechanical analysis of atomistic simulations. Int. J. Solids Struct. 46, 238–253.

[3] Cordier, P., Demouchy, S., Beausir, B., Taupin, V., Barou, F., Fressengeas, C., 2014. Disclinations provide the missing mechanism for deforming olivine-rich rocks in the mantle. Nature 507, 51–56.

[4] Adjaoud, O., Marquardt, K., Jahn, S., 2012. Atomic structures and energies of grain boundaries in Mg₂SiO₄ forsterite from atomistic modeling. Phys. Chem. Miner. 39, 749–760.