Monday, December 10, 2012

1212.1544 (Kumar Ankit et al.)

Phase-field study of grain boundary tracking behavior in crack-seal

Kumar Ankit, Britta Nestler, Michael Selzer, Mathias Reichardt
In order to address the vein-growth problem in geology, a multi-phase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a complete understanding, we investigate the influence of various boundary conditions on crystal growth (free-growth and crack-sealing) that result in formation of vein microstructures. To begin with, we consider the anisotropy in surface energy to simulate crystals (with flat facets and sharp corners) possessing different orientations and study the resulting growth competition to deduce a consistent orientation selection rule in the free-growth regime. Next, from crack-sealing simulations, we co-relate the grain boundary tracking behavior and the relative rates of crack opening and trajectory, initial grain size and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small and crystals touch the wall before the next crack increment starts. Further, it is found that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack opening velocity is increased and wall roughness is not sufficiently high.
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