High-speed ultrasound imaging in dense suspensions reveals impact-activated solidification due to dynamic shear jamming

Abstract

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 behaviour. On the basis of 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.

Dynamic shear jamming in dense granular suspensions under extension

“…We see a correlated region of high velocity [indicated by dark red (gray) region] that grows with time and finally interacts with the container bottom (horizontal dashed lines in Fig. 4a-h) similar to the jammed region observed under impact [5,19]. In Fig.…”

“…Mapping out the full 3-D strain rate tensor [19] we find that a high shear rate (both pure and simple shear) region having much larger magnitude than the rate of expansion component is formed at the edge of the growing jammed region ( Fig. 8 and also see Movie 3 in [16]).…”

“…This implies that any packing fraction change could at most have been ∆φ ∼ 0.01-0.02. Given that we start in our experiments from a fluid state that has a φ significantly below the packing fraction for jamming by compression of the particle subphase, such small ∆φ is insufficient to solidify the system and instead the jamming is primarily shear induced [19].…”

Uncovering Instabilities in the Spatiotemporal Dynamics of a Shear-Thickening Cornstarch Suspension

“…Dense starch suspensions are a popular system to investigate shear thickening [32][33][34][35][36][37][38], even though they raise technical challenges linked to particle polydispersity and porosity, to sedimentation and potential migration under shear, or to possible adhesion between particles [26,39,40]. Using a rheometer in a concentriccylinder geometry, we solicit the suspension at a constant shear stress and simultaneously image the local flow behavior at a "mesoscopic" scale of a few particle sizes with ultrasonic echography.…”

Preface: Focus on imaging methods in granular physics

“…63 Still, velocity fields have been recently obtained in dense suspensions using high-speed ultrasound imaging. 64 …”