Viscous-like forces control the impact response of shear-thickening dense suspensions

We experimentally and theoretically study impacts into dense cornstarch and water suspensions. We vary impact speed as well as intruder size, shape and mass, and we characterize the resulting dynamics using high-speed video and an onboard accelerometer. We numerically solve previously proposed models, most notably the added-mass model as well as a class of viscous-like models. In the viscous-like models, the intruder dynamics is dominated by large, viscous-like forces at the boundary of the jammed front where large shear rates and accompanying large viscosities are present. We find that our experimental data are consistent with this class of models and inconsistent with the added-mass model. Our results strongly suggest that the added-mass model, which is the dominant model for understanding the dynamics of impacts into shear-thickening dense suspensions, should be updated to include these viscous-like forces.