Vidar Skogvoll (University of Oslo): "A phase-field crystal framework for 3D dislocation dynamics"
Abstract:
The Phase Field Crystal (PFC) model is a versatile approach to study the dynamics of defected crystalline materials in terms of kinematics of dislocations, grain boundaries and fracture dynamics. The PFC model has minimal assumptions based on representing a crystal lattice symmetry by an order parameter that minimizes an appropriate free energy at equilibrium, and that relaxes diffusively in out-of-equilibrium conditions. In this formalism, lattice defects and their properties are determined by the PFC free energy and the dynamics of the order parameter. A challenge with this description is to model dislocation dynamics in the presence of elastic fields and connecting that with continuum elasticity and plasticity descriptions.
In this talk, I will present a general method to identify dislocations in the crystal order parameter and derive expressions for the dislocation density tensor and its dynamics in terms of the evolution of the order parameter. These methods have been used to study the shrinkage of a shear dislocation loop in a bcc lattice.
Marcel Moura (University of Oslo): "Capillary pumping: the spreading of pollution in porous media"
Abstract:
When a wet portion of the soil gets dry, say after some hours of sunshine following a storm, thin liquid films remain on the surface of the soil grains. These thin films bring an interesting consequence: they can interconnect different parts of the soil, like a whole set of water bridges forming a large network of water streets and avenues. This analogy may seem a bit far-fetched but it is quite descriptive: just like our streets, the water films act as an invisible transportation network. Plant roots can use this network to obtain nutrients from far away, but pollutants can also take a high-speed road to spread quickly in the soil. We are interested in understanding the dynamics of the transport of polluted water through a network of thin water films in a porous medium. This is analogous to the scenario in which some polluted water is spilled on the ground and starts to seep through the porous space. As natural soils are unfortunately not transparent, we employ artificial porous samples in our study (either made of glass or 3D printed in a transparent plastic). We have performed some preliminary experiments and observed that the residual water content in the sample (how wet or dry the soil is) plays a key role in the pollution spreading dynamics. We have found that for intermediate residual water content, the thin liquid films in the sample behave as a network of tiny pumps, which act to spread the pollution very quickly.
You will find the complete schedule for Njord Seminar Series spring '22 here.
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