Grain boundaries do it all. They transmit stresses,they move under the action of an applied stress,they migrate when curved, they slide, they roughen,they transmit/absorb/emit dislocations,... They are central to the mechanical behavior of poly-crystalline materials. They behave differently at low temperature and high temperature, with different grain miss-orientations, with different inclinations,... I will present a bi-crystallography-based model for the structure and kinetic properties of grain boundaries that rationalizes many grain boundary properties within a single coherent picture. The model is based on the migration of a type of line defects that only exist in the grain boundary, known as disconnections.Finally, I will review some recent progress in moving from a discrete disconnection-level description of grain boundaries to a continuum model.
