Viscous dissipation in large amplitude oscillatory shear of unsaturated wet granular matter

The present work investigates nonlinear behavior in large amplitude oscillatory shear (LAOS) of unsaturated wet granular materials using pressure-imposed rheometric measurements that enable to explore how the material properties characterizing the flow response depend on both strain amplitude and frequency of deformation. Away from the quasistatic limit, we show that the energy dissipated per unit volume in a single LAOS cycle, which can be visualized by the area enclosed by the Lissajous curve of stress versus strain, is an increasing function of the viscosity of the wetting liquid and is also influenced by the reduced pressure (comparing the cohesive to confining forces) and the frequency. Introducing the inertial number $I$ and the viscous number $Iv$ as previously done, it is shown that the influence of surface tension, viscosity, and driving frequency can be captured by plotting the dissipated energy per unit volume versus the viscous number: a good collapse is obtained. It is shown that an increase in liquid content shifts the whole curve of the dissipated energy upwards, indicating that the overall dissipation mechanism does not change with liquid content, only the energy dissipation related to the internal structure and its breakdown changes.