Non-linear viscoelastic response of magnetic fiber suspensions in oscillatory shear
نویسندگان
چکیده
This paper reports the first study on the large amplitude oscillatory shear flow for magnetic fiber suspensions subject to a magnetic field perpendicular to the flow. The suspensions used in our experiments consisted of cobalt microfibers of the average length of 37 μm and diameter of 4.9 μm, dispersed in a silicon oil. Rheological measurements have been carried out at imposed stress using a controlled stress magnetorheometer. The stress dependence of the shear moduli presented a staircase-like decrease with, at least, two viscoelastic quasiplateaus corresponding to the onset of microscopicand macroscopic scale rearrangement of the suspension structure, respectively. The frequency behavior of the shear moduli followed a power-law trend at low frequencies and the storage modulus showed a high-frequency plateau, typical for Maxwell behavior. Our simple single relaxation time model fitted reasonably well the rheological data. To explain a relatively high viscous response of the fiber suspension, we supposed a coexistence of percolating and pivoting aggregates. Our simulations revealed that the former became unstable beyond some critical stress and broke in their middle part. At high stresses, the free aggregates were progressively destroyed by shear forces that contributed to a drastic decrease of the moduli. We have also measured and predicted the output strain waveforms and stress-strain hysteresis loops. With the growing stress, the shape of the stress-strain loops changed progressively from near-ellipsoidal one to the rounded-end rectangular one due to a progressive transition from a linear viscoelastic to a viscoplastic Bingham-like behavior.
منابع مشابه
Rheological Measurement of Concentrated Pulp Fiber Suspensions in Oscillatory Shear Using a Novel Device
This paper presents a novel device based on an oscillating torsion resonator with continuously varying frequency capability to characterize the rheological properties of pulp fiber suspensions in a concentrated regime. Fiber suspensions made from unbleached wheat straw pulp at concentrations ranging from 5 wt% to 15 wt% were used. Pulp suspensions exhibit shear-thinning behavior up to a limited...
متن کاملElectrokinetic and viscoelastic properties of magnetorheological suspensions of cobalt ferrite
Magnetorheological suspensions are among the most promising colloidal systems from the point of view of their many potential technological applications. Most studies on these systems have, however, been performed using a non-polar liquid as dispersion medium. In this work we consider aqueous suspensions of synthetic, spherical cobalt ferrite particles. From electrophoretic mobility determinatio...
متن کاملViscoelastic properties of wheat gliadin and glutenin suspensions
Linear and non-linear rheological properties of wheat gliadin and glutenin suspensions were investigated at various concentrations. Linear dynamic viscoelastic properties for both gliadin and glutenin were strongly dependent on concentration. For gliadins, the storage moduli (G 0), loss moduli (G00), and phase shifts dramatically changed within a narrow concentration range, indicating that glia...
متن کاملRestructuring and aging in a capillary suspension.
The rheological properties of capillary suspensions, suspensions with small amounts of an added immiscible fluid, are dramatically altered with the addition of the secondary fluid. We investigate a capillary suspension to determine how the network ages and restructures at rest and under applied external shear deformation. The present work uses calcium carbonate suspended in silicone oil (11 % s...
متن کاملDynamic Response of an Axially Moving Viscoelastic Timoshenko Beam
In this paper, the dynamic response of an axially moving viscoelastic beam with simple supports is calculated analytically based on Timoshenko theory. The beam material property is separated to shear and bulk effects. It is assumed that the beam is incompressible in bulk and viscoelastic in shear, which obeys the standard linear model with the material time derivative. The axial speed is charac...
متن کامل