Viscometers for measuring the viscosities of non-Newtonian complex fluids using innovative granular metafluids

We developed an innovative experimental setup that serves as a viscometer for granular mixtures under conditions in which solid and liquid phases coexist. Our findings show that fine grains in a container exhibit rotational motion analogous to a liquid in rigid-body rotation when exposed to low-peak accelerations from high-frequency horizontal vibrations. This behavior produces a thin boundary layer within the granular mixture that separates the bulk material from the container wall and exhibits a distinct shear flow. To estimate viscosity, we implemented a granular metafluid film that effectively emulated the boundary-layer phenomena observed in these mixtures. Utilizing the generalized Green–Kubo formula, we measured the viscosity and compared our results with theoretical predictions for multi-component dense mixtures of slightly inelastic spherical particles. By establishing a clear analogy between our granular metafluid film and semi-solid metal (SSM) samples, our approach lays a constructive foundation for future research in SSM processing, supporting deeper insight and inspiring continued innovation in this field.