Dynamic jamming of dense suspensions under tilted impact

TL;DR

This study extends ultrasound imaging to three dimensions to analyze how impact angles influence the propagation and shape of jamming fronts in dense suspensions, revealing boundary effects and non-axisymmetric behaviors.

Contribution

It introduces a 3D ultrasound imaging method to study non-axisymmetric jamming fronts caused by tilted impacts in dense suspensions.

Findings

Flow fields are similar to normal impact when far from boundaries.

Impact angle affects the shape and propagation of jamming fronts.

Boundary proximity causes non-axisymmetric deformation of the front.

Abstract

Dense particulate suspensions can not only increase their viscosity and shear thicken under external forcing, but also jam into a solid-like state that is fully reversible when the force is removed. An impact on the surface of a dense suspension can trigger this jamming process by generating a shear front that propagates into the bulk of the system. Tracking and visualizing such a front is difficult because suspensions are optically opaque and the front can propagate as fast as several meters per second. Recently, high-speed ultrasound imaging has been used to overcome this problem and extract two-dimensional sections of the flow field associated with jamming front propagation. Here we extend this method to reconstruct the three-dimensional flow field. This enables us to investigate the evolution of jamming fronts for which axisymmetry cannot be assumed, such as impact at angles tilted away from the normal to the free surface of the suspension. We find that sufficiently far from solid boundaries the resulting flow field is approximately identical to that generated by normal impact, but rotated and aligned with the angle of impact. However, once the front approaches the solid boundary at the bottom of the container, it generates a squeeze flow that deforms the front profile and causes jamming to proceed in a non-axisymmetric manner.