Probing the effect of particle shape on the rigidity of jammed granular solids with sound speed measurements

Abstract

We describe a precise phase velocity measurement of longitudinal sound waves in granular solids under stress. We observe an important difference of the phase velocity between the packings of glass beads and sand particles, which is likely due to the interlocking effect caused by the particle shape. This effect can be captured by the contact coordination number using the effective medium theory. We also investigate the change of this coordination number in dry and wet granular packings, caused by cyclic loading or nonlinear sound transmission. These acoustic measurements show that the particle-level properties such as shape and friction significantly influence the response of jammed granular solids to external driving.

Distinguishing between rheophysical regimes of fluid-saturated granular-flows using dilatancy and acoustic emission measurements

“…analysis and the flow should be under the frictional-collisional regime [11]. The water-saturated, high-velocity experiments are less extreme with Sa' ~ 1, Ba ~ 10 2 and Le ~ 10 -3 suggesting the flow is in the frictional-collisional regime but perhaps the inference is less definitive because of the more moderate Bagnold number.…”

“…Ancey et al [11] suggest that the competing processes in the flow are: (1) friction, (2) granular pressure and (3) lubrication pressure. Approximating each of these forces using a linearization of the governing equations, results in an order of magnitude approximation.…”

“…In addition, hydrodynamic lubrication can change the internal pressure of the shear flow and therefore the macroscopic behavior [27][28][29][30][31]. To compare the magnitude of frictional and lubricated forces we follow Ancey et al [11] and use the Leighton number, assuming that the minimum gap between particles (ε) is on the order of d/λ: For Le >> 1 and Ba << 1, granular flows should be controlled by hydrodynamic effects [11].…”

“…Theory provides some guidance on expected flow regimes. Non-dimensional parameters based on linearizing the governing equations delineate anticipated dynamical regimes [8][9][10][11]. The approach is powerful and forms the foundation of fluid dynamics.…”

Transient Dynamics of Concentrated Particulate Suspensions Under Shear

“…Combined with steady-state rheology, ultrasound speckle velocimetry has been used to measure the flow field [61,62]. The transmission of compression or shear waves can be used to probe the mechanical properties of jammed granular materials [63,64,65,66]. As a well developed technique, ultrasound has a lot of potential for soft matter experiments, especially for aqueous but optically opaque materials.…”