Abstract
Granular materials whether dry or immersed in fluid show dilation or compaction depending upon the initial conditions, solid fraction and normal stress. Here we probe the transient response of a dense granular suspension subjected to change of applied normal stress under simple shear. In this aim, normal-stress-imposed discrete element particle simulations are developed considering the contributions arising from the drag induced on the particles by fluid phase. These pressure-imposed simulations show transient behaviors of dense granular suspensions such as dilation or compaction before reaching a steady state following the µ(J) rheology. Less expectedly, the transient behavior, in particular the height of the system as a function of applied strain, can also be described by assuming that the system follows the steady µ(J) rheology at all times.
Highlights
Understanding and predicting the rheology of dense granular suspensions is highly important to understand the behavior of e.g. debris or mud flows [1]
For an homogeneous mixture of non-Brownian and neutrally-buoyant rigid particles in a viscous fluid, dimensional analysis shows that in simple shear the rheology is described by a couple of relations expressing the macroscopic friction μ = τ/Pp and the solid fraction φ as a function of the so-called viscous number J = ηfγ /Pp
Because φSS(J) < 0, the μ(J) rheology captures the change of volume for the particle phase between two steady states, that is, dilation under increase of J [4], a phenomenon observed in immersed soils [5, 6] or submarine avalanches [1, 7]
Summary
Understanding and predicting the rheology of dense granular suspensions is highly important to understand the behavior of e.g. debris or mud flows [1]. It finds application in civil, mining and food engineering sectors while handling concrete, drilling muds, petroleum extraction and manufacturing of chocolates and other food products [2]. We developed DEM simulations of a simple shear of a granular suspension under imposed external particle normal stress Pext. We show that in this setup, the entire dynamics of volumetric change can be well described by the μ(J) rheology, even though this rheology is a priori only valid in steady state
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