Dynamic shear jamming in dense granular suspensions under extension

摘要

Unlike dry granular materials, a dense granular suspension like cornstarch in water can strongly resistextensional flows. At low extension rates, such a suspension behaves like a viscous fluid, but rapid extensionresults in a response where stresses far exceed the predictions of lubrication hydrodynamics and capillarity. Tounderstand this remarkable mechanical response, we experimentally measure the normal force imparted by alarge bulk of the suspension on a plate moving vertically upward at a controlled velocity.We observe that, abovea velocity threshold, the peak force increases by orders of magnitude. Using fast ultrasound imaging we map outthe local velocity profiles inside the suspension, which reveal the formation of a growing jammed region underrapid extension. This region interacts with the rigid boundaries of the container through strong velocity gradients,suggesting a direct connection to the recently proposed shear-jamming mechanism.