Rheology of non-Brownian suspensions of rough frictional particles under shear reversal: A numerical study

Abstract

International audienceWe perform particle scale simulations of suspensions submitted to shear reversal. The simulations are based on the Force Coupling Method, adapted to account for short range lubrication interactions together with direct contact forces between particles, including surface roughness, contact elasticity and solid friction. After shear reversal, three consecutive steps are identified in the viscosity transient: an instantaneous variation, followed by a rapid contact force relaxation, and finally a long time evolution. The separated contributions of hydrodynamics and contact forces to the viscosity are investigated during the transient, allowing a qualitative understanding of each step. In addition, the influence of the contact law parameters (surface roughness height and friction coefficient) on the transient are evaluated. Concerning the long time transient, the difference between the steady viscosity and minimum viscosity is shown to be proportional to the contact contribution to the steady viscosity, allowing in principle easy determination of the latter in experiments. The short time evolution is studied as well. After the shear reversal, the contact forces vanish over a strain that is very short compared to the typical strain of the long time transient, allowing to define an apparent step between the viscosity before shear reversal and after contact force relaxation. This step is shown to be an increasing function of the friction coefficient between particles. Two regimes are identified as a function of the volume fraction. At low volume fraction, the step is small compared to the steady contact viscosity, in agreement with a particle pair model. As the volume fraction increases, the value of the viscosity step increases faster than the steady contact viscosity, and, depending on the friction coefficient, may approach it

X-ray radiography of viscous resuspension

“…As already observed in the literature 29,31,32 , the shear viscosity just after reversal is smaller than the steady-state viscosity and it subsequently increases with strain until it reaches a steady state for a strain of order 5. Figure 10b-c shows that the steady-state viscosity is more sensitive to the shear rate than the viscosity minimum η min reached shortly after shear reversal.…”

“…Indeed, the shear viscosity of the suspension finds its contribution from both hydrodynamic and contact stresses. In order to get some insight into contact stresses, one needs to perform, for example, shear reversal experiments [29][30][31][32] . In such experiments, the suspension is first sheared at a given shear stress or shear rate in a simple shear flow until steady-state is reached.…”

“…Upon shear reversal, all of these contacts are now in traction and are suddenly broken, which results in an abrupt decrease of the viscosity. The minimum viscosity achieved during the reversal can then be associated mostly with hydrodynamic interactions, whereas the difference between the steady-state viscosity and this minimum provides the contact contribution to the viscosity 32 .…”

The role of friction in the yielding of adhesive non-Brownian suspensions

“…A protocol that does show transient yielding, rejamming, and a second, permanent yielding is shear reversal. It has been used to reveal the role of friction in repulsive nB suspensions 41,42 : abruptly reversing the shear direction during steady-state shear breaks all frictional contacts, which are only reformed when a reversed strain of order unity has been accumulated.…”

Linking attractive interactions and confinement to the rheological response of suspended particles close to jamming

“…The detailed evolution of the microstructure in this region, as well as a characterisation of the corresponding stress response (which we presented in Fig. 1c) have been discussed in detail elsewhere [26]. For φ = 0.650 and above, however, the application of shear strain has little effect on the average coordination number.…”