James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.
Nat Commun. 2016 Jul 20;7:12243. doi: 10.1038/ncomms12243.
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.
密集悬浮液的一个显著特性是，它们在静止时可以从液态转变为固态，在突然冲击下。以前的工作表明，这种冲击诱导的固化涉及到快速移动的堵塞前沿;然而，这一过程的细节仍未解决。在这里，我们使用高速超声成像技术来探测密集悬浮液内部对冲击的反应。通过测量声速，我们证明了固化过程中没有可检测到的堆积分数的增加，并且通过对不断发展的流场进行成像，我们发现剪切强度在堵塞前沿处达到最大值。总的来说，这为剪切而不是密实化作为驱动转变为固态行为的驱动力提供了直接的实验证据。基于这些发现，我们提出了一个新的模型来解释前沿传播速度的各向异性，并描绘出悬浮液中动态剪切堵塞的起始条件。
