Moving Boundaries: Classical models of fine-grained metals view grain boundaries as static objects, but this view has been challenged by recent experimental observations. Drawing on techniques used by the fracture mechanics community, Rupert et al. (p. 1686 ) present experiments on freestanding aluminum films that show specific geometries cause either stress or strain concentrations on deformation. Confirming recent simulations, shear stresses were found to be a key driver of grain boundary motion.

We investigate the effects of topological disorder and wettability on fluid displacement in porous media. A modified disorder index $I_v$ is proposed to characterize the disorder of porous media. By changing $I_v$, different displacement patterns (stable displacement and fingering) under the same flow condition and fluid property are obtained. We analytically demonstrate how increase in disorder promotes fingering due to uneven distribution of local capillary pressure. It is shown that the displacement efficiency for different wettability conditions and disorder well correlates with the distribution of local capillary pressure. A power-law relation between fluid-fluid interfacial length and saturation of invading fluid is proposed by taking geometry into account, where the parameters in power-law relation can be predicted by the capillary index, $I_c$, unifying the effects of topological disorder and wettability.