We report experiments investigating jamming fronts in a floating layer of cornstarch suspension. The suspension has a packing fraction close to jamming, which dynamically turns into a solid when impacted at a high speed. We show that the front propagates in both axial and transverse direction from the point of impact, with a constant ratio between the two directions of propagation of approximately 2. Inside the jammed solid, we observe an additional compression, which results from the increasing stress as the solid grows. During the initial growth of the jammed solid, we measure a force response that can be completely accounted for by added mass.

Only once the jamming front reaches a boundary, can the added mass no longer account for the measured force. We do not, however, immediately see a strong force response as we would expect when compressing a jammed packing. Instead, we observe a delay in the force response on the pusher, which corresponds to the time it takes for the system to develop a

close to uniform velocity gradient that spans the complete system.

1. •I. R. Peters and H. M. Jaeger, “Quasi-2D dynamic jamming in cornstarch suspensions: visualization and force measurements”, Soft Matter 10, 6564–6570 (2014). pdf file