ABSTRACT
Non-Newtonian fluids can be used for the protection of flexible laminates. Understanding the coupling between the flow of the protecting fluid and the deformation of the protected solids is necessary in order to optimize this functionality. We present a scaling analysis of the problem based on a single coupling variable, the effective width of a squeeze flow between flat rigid plates, and predict that impact protection for laminates is optimized by using shear-thinning, and not shear-thickening, fluids. The prediction is verified experimentally by measuring the velocity and pressure in impact experiments. Our scaling analysis should be generically applicable for non-Newtonian fluid-solid interactions in diverse applications.
ABSTRACT
Dense suspensions often become more dilute as they move downstream through a constriction. We find that as a shear-thickening suspension is extruded through a narrow die and undergoes such liquid migration, the extrudate maintains a steady concentration Ï_{out}^{LM}, independent of time or initial concentration. At low volumetric flow rate Q, Ï_{out}^{LM} is a universal function of Q/r_{d}^{3}, a characteristic shear rate in the die of radius r_{d}, and coincides with the critical input concentration for the onset of LM, Ï_{in}^{crit}. We predict this function by coupling the Wyart-Cates model for shear thickening and the "suspension balance model" for solvent permeation through particles.
