Ultrasonic attenuation and speed of sound of cornstarch suspensions

Johnson, B. Lamar; Holland, Mark; Miller, James G.; Katz, J. I.

doi:10.1121/1.4789926

Cited by 10 publications

(7 citation statements)

References 38 publications

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“…Again, this supports our argument that there exists a pressure front in the suspension, separate from the mass shock, which precedes it and which may propagate forces to the suspension boundary before the arrival of the mass shock. The pressure wave speeds observed here, which are ∼ 10 2 m/s for frequencies ∼ kHz, differ substantially from ultrasound data [25,26] for the sound speed, e.g. sounds speeds of ∼ 1.7 × 10 3 m/s at frequencies in the M Hz range.…”

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confidence: 71%

Force and Mass Dynamics in Non-Newtonian Suspensions

et al. 2017

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Above a certain solid fraction, dense granular suspensions in water exhibit non-Newtonian behavior, including impact-activated solidification. Although it has been suggested that solidification depends on boundary interactions, quantitative experiments on the boundary forces have not been reported. Using high-speed video, tracer particles, and photoelastic boundaries, we determine the impactor kinematics and the magnitude and timings of impactor-driven events in the body and at the boundaries of cornstarch suspensions. We observe mass shocks in the suspension during impact. The shock front dynamics are strongly correlated to those of the intruder. However, the total momentum associated with this shock never approaches the initial impactor momentum. We also observe a faster second front associated with the propagation of pressure to the boundaries of the suspension. The two fronts depend differently on the initial impactor speed v_{0} and the suspension packing fraction. The speed of the pressure wave is at least an order of magnitude smaller than (linear) ultrasound speeds obtained for much higher frequencies, pointing to complex amplitude and frequency response of cornstarch suspensions to compressive strains.

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confidence: 71%

Force and Mass Dynamics in Non-Newtonian Suspensions

et al. 2017

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“…In the limit that the solid particles are much smaller than the wavelength, the speed of sound is then given by , where K is the average bulk modulus and ρ the average material density of the suspension 22 23 . In our experiments, the particles and suspending solvent are density matched (see Methods section), but the average K still increases with ϕ since cornstarch particles have a bulk modulus larger than that of the liquid 24 . As shown in Fig.…”

Section: Resultsmentioning

confidence: 96%

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

2016

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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.

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“…This implies minimal particle-liquid surface tension and consequent shear thinning effects in water (Brown et al, 2010a), which also happens to have one of the highest surface tensions of common liquids. Cornstarch remains an inert, hard particle (with Young's modulus around 10 GPa (Johnson et al, 2013)), in contrast to some other mass-produced powders such as flour, which gels in water at room temperature. Thus we attribute the strong shear thickening of cornstarch to its optimal particle size and lack of the various interactions which produce shear thinning effects that could hide shear thickening.…”

Section: State Diagrammentioning

confidence: 99%

Shear thickening in concentrated suspensions: phenomenology, mechanisms and relations to jamming

2014

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Shear thickening is a type of non-Newtonian behavior in which the stress required to shear a fluid increases faster than linearly with shear rate. Many concentrated suspensions of particles exhibit an especially dramatic version, known as Discontinuous Shear Thickening (DST), in which the stress suddenly jumps with increasing shear rate and produces solid-like behavior. The best known example of such counter-intuitive response to applied stresses occurs in mixtures of cornstarch in water. Over the last several years, this shear-induced solid-like behavior together with a variety of other unusual fluid phenomena has generated considerable interest in the physics of densely packed suspensions. In this review, we discuss the common physical properties of systems exhibiting shear thickening, and different mechanisms and models proposed to describe it. We then suggest how these mechanisms may be related and generalized, and propose a general phase diagram for shear thickening systems. We also discuss how recent work has related the physics of shear thickening to that of granular materials and jammed systems. Since DST is described by models that require only simple generic interactions between particles, we outline the broader context of other concentrated many-particle systems such as foams and emulsions, and explain why DST is restricted to the parameter regime of hard-particle suspensions. Finally, we discuss some of the outstanding problems and emerging opportunities.

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Ultrasonic attenuation and speed of sound of cornstarch suspensions

Cited by 10 publications

References 38 publications

Force and Mass Dynamics in Non-Newtonian Suspensions

Force and Mass Dynamics in Non-Newtonian Suspensions

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

Shear thickening in concentrated suspensions: phenomenology, mechanisms and relations to jamming

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