A remarkable property of dense suspensions is that they can transform from liquid-like at rest

to solid-like under sudden impact. Previous work showed that this impact-induced solidification

involves rapidly moving jamming fronts; however, details of this process have remained unresolved. Here we use high-speed ultrasound imaging to probe non-invasively how the interior

of a dense suspension responds to impact. Measuring the speed of sound we demonstrate that

the solidification proceeds without a detectable increase in packing fraction, and imaging the

evolving flow field we find that the shear intensity is maximized right at the jamming front.

Taken together, this provides direct experimental evidence for jamming by shear, rather than

densification, as driving the transformation to solid-like behavior.

Based on these findings we propose a new model to explain the anisotropy in the propagation speed of the fronts and delineate the onset conditions for dynamic shear jamming in suspensions.

1. •Endao Han, Ivo R. Peters, and Heinrich M. Jaeger, “High-speed ultrasound imaging in dense suspensions reveals impact-activated solidification due to dynamic shear jamming”. preprint