Dynamic shear jamming in dense granular suspensions under extension

TL;DR

This study investigates how dense granular suspensions like cornstarch in water resist rapid extension, revealing a shear-jamming transition characterized by a growing jammed region and significant force increase.

Contribution

The paper experimentally demonstrates the formation of a shear-jammed region during rapid extension in dense suspensions, linking it to boundary interactions and velocity gradients.

Findings

Force increases dramatically above a velocity threshold

Ultrasound imaging shows a growing jammed region

Strong boundary velocity gradients are observed

Abstract

Unlike dry granular materials, a dense granular suspension like cornstarch in water can strongly resist extensional flows. At low extension rates, such a suspension behaves like a viscous liquid, but rapid extension results in a response where stresses far exceed the predictions of lubrication hydrodynamics and capillarity. To understand this remarkable mechanical response, we experimentally measure the normal force imparted by a large bulk of the suspension on a plate moving vertically upward at a controlled velocity. We observe that above a velocity threshold, the peak force increases by orders of magnitude. Using fast ultrasound imaging we map out the local velocity profiles inside the suspension which reveal the formation of a growing jammed region under rapid 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.