Waitukaitis, Scott RIST Austria ; Jaeger, Heinrich
Although liquids typically flow around intruding objects, a counterintuitive phenomenon occurs in dense suspensions of micrometre-sized particles: they become liquid-like when perturbed lightly, but harden when driven strongly. Rheological experiments have investigated how such thickening arises under shear, and linked it to hydrodynamic interactions or granular dilation. However, neither of these mechanisms alone can explain the ability of suspensions to generate very large, positive normal stresses under impact. To illustrate the phenomenon, such stresses can be large enough to allow a person to run across a suspension without sinking, and far exceed the upper limit observed under shear or extension. Here we show that these stresses originate from an impact-generated solidification front that transforms an initially compressible particle matrix into a rapidly growing jammed region, ultimately leading to extraordinary amounts of momentum absorption. Using high-speed videography, embedded force sensing and X-ray imaging, we capture the detailed dynamics of this process as it decelerates a metal rod hitting a suspension of cornflour (cornstarch) in water. We develop a model for the dynamic solidification and its effect on the surrounding suspension that reproduces the observed behaviour quantitatively. Our findings suggest that prior interpretations of the impact resistance as dominated by shear thickening need to be revisited.
This work was supported by NSF through its MRSEC programme (DMR-0820054) and by the US Army Research Office through grant number W911NF-12-1-0182. S.R.W. acknowledges support from a Millikan fellowship.
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Waitukaitis SR, Jaeger H. Impact-activated solidification of dense suspensions via dynamic jamming fronts. Nature. 2012;487(7406):205-209. doi:10.1038/nature11187
Waitukaitis, S. R., & Jaeger, H. (2012). Impact-activated solidification of dense suspensions via dynamic jamming fronts. Nature, 487(7406), 205–209. https://doi.org/10.1038/nature11187
Waitukaitis, Scott R, and Heinrich Jaeger. “Impact-Activated Solidification of Dense Suspensions via Dynamic Jamming Fronts.” Nature 487, no. 7406 (2012): 205–9. https://doi.org/10.1038/nature11187.
S. R. Waitukaitis and H. Jaeger, “Impact-activated solidification of dense suspensions via dynamic jamming fronts,” Nature, vol. 487, no. 7406, pp. 205–209, 2012.
Waitukaitis SR, Jaeger H. 2012. Impact-activated solidification of dense suspensions via dynamic jamming fronts. Nature. 487(7406), 205–209.
Waitukaitis, Scott R., and Heinrich Jaeger. “Impact-Activated Solidification of Dense Suspensions via Dynamic Jamming Fronts.” Nature, vol. 487, no. 7406, Nature Publishing Group, 2012, pp. 205–09, doi:10.1038/nature11187.