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We report direct measurements of spatially resolved stress at the boundary of a shear-thickening cornstarch suspension revealing persistent regions of high local stress propagating in the flow direction at the speed of the top boundary. The persistence of these propagating fronts enables precise measurements of their structure, including the profile of boundary stress measured by boundary stress microscopy (BSM) and the nonaffine velocity of particles at the bottom boundary of the suspension measured by particle image velocimetry (PIV). In addition, we directly measure the relative flow between the particle phase and the suspending fluid (fluid migration) and find the migration is highly localized to the fronts and changes direction across the front, indicating that the fronts are composed of a localized region of high dilatant pressure and low particle concentration. The magnitude of the flow indicates that the pore pressure difference driving the fluid migration is comparable to the critical shear stress for the onset of shear thickening. The propagating fronts fully account for the increase in viscosity with applied stress reported by the rheometer and are consistent with the existence of a stable jammed region in contact with one boundary of the system that generates a propagating network of percolated frictional contacts spanning the gap between the rheometer plates and producing strong localized dilatant pressure.
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This content will become publicly available on May 1, 2026
Transient shear-jammed clusters in shear-thickening suspensions
Dense particulate suspensions demonstrate a significant increase in average viscosity beyond a material-specific critical shear stress. Here, we analyze the steady-state structure of a suspension of monodisperse silica microspheres in the shear-thickening regime. Using dynamic measurement of boundary stress, we show that the flow is characterized by a cluster of high-stress fronts that propagate in the flow direction at a speed of 1/2 relative to the top plate of the rheometer. We apply high-speed line scan imaging to reveal dramatic fluctuations in particle speed, ordering, and concentration associated with the fronts and show that the structure is consistent with transiently jammed networks that contain high interparticle stresses that percolate across the rheometer gap, but which are present only briefly during the passage of the high-stress fronts.
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- PAR ID:
- 10657472
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- Journal of Rheology
- Volume:
- 69
- Issue:
- 3
- ISSN:
- 0148-6055
- Page Range / eLocation ID:
- 343 to 352
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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