Macroscopic rheology of non-Brownian suspensions at high shear rates: the influence of solid volume fraction and non-Newtonian behaviour of the liquid phase

Modelling the macroscopic rheology of non-Brownian suspensions is complicated by the non-linear behaviour that originates from the interaction between solid particles and the liquid phase. In this contribution, a model is presented that describes suspension rheology as a function of solid volume fraction and shear rate dependency of both the liquid phase, as well as the suspension as a whole. It is experimentally validated using rotational rheometry ($$\varphi$$ φ ≤ 0.40) and capillary rheometry (0.55 ≤ $$\varphi$$ φ ≤ 0.60) at shear rates > 50 s−1. A modified Krieger-Dougherty relation was used to describe the influence of solid volume fraction on the consistency coefficient, $$K$$ K , and was fitted to suspensions with a shear thinning liquid phase, i.e. having a flow index, $$n$$ n , of 0.50. With the calculated fit parameters, it was possible to predict the consistency coefficients of suspensions with a large variation in the shear rate dependency of the liquid phase ($$n$$ n = 0.20–1.00). With increasing solid volume fraction, the flow indices of the suspensions were found to decrease for Newtonian and mildly shear thinning liquid phases ($$n$$ n ≥0.50), whereas they were found to increase for strongly shear thinning liquid phases ($$n$$ n ≤0.27). It is hypothesized that this is related to interparticle friction and the relative contribution of friction forces to the viscosity of the suspension. The proposed model is a step towards the prediction of the flow curves of concentrated suspensions with non-Newtonian liquid phases at high shear rates.

Investigation of the well-dispersed magnetorheological oil-based suspension with superparamagnetic nanoparticles using modified split Hopkinson pressure bar

Magnetorheological (MR) fluids are classified as smart materials whose viscoplastic characteristics change under the magnetic field. They are widely applied for dynamic energy dissipation due to their rapid thickening under the external magnetic field. In this work, the core–shell suspension of superparamagnetic iron oxide-based nanoparticles was synthesized and dispersed in silicone oil. Much effort has been made to prepare suspension meeting requirements of MR fluid. The experimental squeezing flow response was studied using a modified split Hopkinson pressure bar (SHPB) with various shear rates. Tests with modified SHPB show that MR fluid rapidly responds to the compression thickening and forming chain-like structures. MR fluid dissipates the energy generated during compression stress tests. This study presents a simple and cost-effective synthesis way suitable for MR fluid formation for its dynamic energy dissipation application.