Effect of Lubrication on Quakes in Granular Materials

Granular materials deform via transient quakes or slips between its particles when compressed. We investigate a remarkable phenomenon in wetted granular materials, where the frequency and magnitude of quakes dramatically increases in an intermediate lubrication regime, in contrast to completely dry or heavily wetted grains, where quakes are much less prominent. Through friction measurements between particle surfaces, we find that this occurs due to the emergence of stick-slip behavior in the boundary lubrication regime between particle contacts. The nonmonotonic effect of lubrication on quakes provides a novel mechanism by which the mechanical response of the material, when driven out of equilibrium, may be tuned by the tribology of granular contacts. This may be leveraged to understand the effect of wetting on quake behavior across scales.