Intrusion into granular-fluid mixtures: testing added-mass and Darcy-Reynolds theories

We present experimental and theoretical results for impact into two related but distinct systems: (1) cornstarch and water suspensions and (2) beds of glass beads immersed in glycerol-water mixtures. For (1), we find that the predominant theoretical paradigm, the added-mass model, does not capture several important features of the experimental data. Instead, we show that theories based on large viscous forces operating at the boundary of a growing, jammed region better explains the experimental results. For (2), we find that the predominant theory, Darcy-Reynolds, performs very well over a wide range of particle sizes. We also find that our experimental results for varied viscosity are consistent with Darcy- Reynolds theory, but only for a limited range of the viscosity. For large viscosities, observed forces begin to decrease with increasing viscosity, in contrast with the theoretical prediction.