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Seminar by Dr. Sayantan Majumdar

Monday, October 24, 2016 - 15:30
SPS Seminar Room
Dr. Sayantan Majumdar
University of Chicago

Unlike dry granular materials, a dense granular suspension like  cornstarch in water can strongly resist extensional flows. At low  extension rates, such a suspension behaves like a viscous fluid, but rapid extension results in a response where stresses far exceed  the predictions of lubrication hydro-dynamics and capillarity. To  understand this remarkable mechanical response, we experimentally  measure the normal force imparted by a large bulk of the suspension  on a plate moving vertically upward at a controlled velocity. We observe  that above a velocity threshold, the peak force increases by orders of  magnitude. Using fast ultrasound imaging we map out the local velocity  profiles inside the suspension which reveal the formation of a growing jammed region under rapid extension. Mapping out the full 3-D strain-rate tensor,  we further show that the accumulation of high shear rate components at  the edge of the jammed region. This suggest a direct connection to the  recently proposed shear-jamming mechanism.

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