ELECTRO-MAGNETORHEOLOGICAL FLUIDS DISPERSING ZEOLITE PARTICLES  CONTAINING IRON

Some functional fluids that respond to both magnetic and electric fields have been prepared and their characteristics are described. In this study, an electro-magnetorheological fluid (EMRF) dispersing zeolite particles containing metallic iron by reducing precipitated magnetite has been investigated. When the viscosity is measured by cone plate viscometer and cylindrical viscometer, electric and magnetic fields are applied both between cone and plate or two cylinders. In case of cone plate, the shear stress at constant shear rate increased with the increase of both magnetic field and electric field. On the other hand when the viscosity is measured by cylindrical viscometer, the shear stress at constant shear rate increased with the increase of electric field, however, the increase rate of shear stress by magnetic field is very small. In this case the magnetic field direction is perpendicular to electric field. The EMRF has typical characteristics to respond with magnetic and electric field. The shear stress of EMRF in electric field is stronger than that of magnetic field. Additionally, the inflection and peak point in the shear rate-shear stress curve are appeared and the behaviors of the clusters in the electric field are observed. The experimental results suggested that the fluid viscosity (shear stress/shear rate) is affected by the arrangement of clusters parallel or perpendicular to the direction of the EMRF flow.

Download Full-text

Plastic Deformation Kinetics of 95.5Sn4Cu0.5Ag Solder Joints

Journal of Electronic Packaging ◽

10.1115/1.2792074 ◽

1995 ◽

Vol 117 (2) ◽

pp. 100-104 ◽

Cited By ~ 24

Author(s):

Z. Guo ◽

Yi-Hsin Pao ◽

H. Conrad

Keyword(s):

Plastic Deformation ◽

Shear Stress ◽

Shear Rate ◽

Solder Joints ◽

Deformation Kinetics ◽

Constant Shear ◽

Controlling Mechanism ◽

Deformation Equation ◽

Kinetics Of ◽

Constant Shear Rate

The plastic deformation kinetics of 95.5Sn4Cu0.5Ag solder joints were determined in monotonic loading shear over the temperature range of 25°–150°C using three types of tests: (a) constant shear rate, (b) constant shear stress (creep), and (c) differential tests (changes in shear rate or temperature during an otherwise isothermal constant shear rate test). The deformation kinetics were evaluated in terms of the Dorn high temperature plastic deformation equation γ˙p=A(μb/kT)D(b/d)P(τ/μ)n where γ˙p is the shear rate, μ the shear modulus, b the Burgers vector, D the appropriate diffusion coefficient, d the grain size and τ the shear stress. A, p, and n are constants whose values depend on the rate controlling mechanism. It was found that n increased with stress from ~4 at 2 MPa to ~20 at 25 MPa, relatively independent of temperature. The activation ΔH was determined to be 21.1 ± 2 kcal/mole. The constant A, however, decreased with temperature from a value of ~1018 at 25°C to ~1010 at 150°C. The values of n and ΔH suggest that dislocation glide and climb is the rate controlling mechanism and hence that p ≈ 0. It is speculated that the large decrease in A with temperature may be the result of an effect on the microstructure.

Download Full-text

Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

Applied Rheology ◽

10.1515/arh-2008-0017 ◽

2008 ◽

Vol 18 (5) ◽

pp. 53298-1-53298-13

Author(s):

Daniel Quemada

Keyword(s):

Shear Stress ◽

Shear Rate ◽

Volume Fraction ◽

Complex Fluids ◽

Transient Behaviour ◽

Volume Fractions ◽

Constant Shear ◽

Constant Shear Stress ◽

Constant Shear Rate ◽

Viscosity Changes

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ > σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

Download Full-text

Shear Flow and Large Amplitude Oscillation Shear Study of Solutions of Aggregating Micellar Casein Particles

Applied Rheology ◽

10.1515/arh-2008-0005 ◽

2008 ◽

Vol 18 (2) ◽

pp. 23050-1-23050-7 ◽

Cited By ~ 1

Author(s):

Anne Pitkowski ◽

Taco Nicolai ◽

Dominique Durand

Keyword(s):

Shear Stress ◽

Shear Rate ◽

Shear Flow ◽

Heating Temperature ◽

Constant Shear ◽

Micellar Casein ◽

Large Amplitude Oscillation ◽

Increasing Temperature ◽

Small Shear ◽

Constant Shear Rate

Abstract Small micellar casein particles were formed in aqueous solutions of native casein after addition of polyphosphate. These so-called submicelles aggregated and gelled with a rate that increased with increasing temperature. The evolution of the viscosity during this process was determined at constant shear rate or shear stress. When applying a small shear stress the viscosity increased strongly until the shear rate became immeasurably slow, but when the applied shear stress exceeded a critical value (σc) the aggregates broke up and the viscosity reached a maximum. At longer times the viscosity decreased rapidly at first, followed by a very slow decrease. σc was independent of the shear rate and heating temperature, but increased strongly with increasing casein concentration. At constant shear rate the stress remained close to σc, but fluctuated irregularly. After cessation of shear flow, gels were formed rapidly. Oscillation shear measurements for σ > σc showed a strongly non-linear response at the time of maximum viscosity.

Download Full-text

ELECTRORHEOLOGY OF DISPERSIONS OF BaxSr(1-x)TiO3 IN SILICONE OIL UNDER AC OR DC ELECTRIC FIELD

International Journal of Modern Physics B ◽

10.1142/s0217979212500816 ◽

2012 ◽

Vol 26 (14) ◽

pp. 1250081 ◽

Cited By ~ 1

Author(s):

GLAUBER M. S. LUZ ◽

ANTONIO J. F. BOMBARD ◽

SILVIO L. M. BRITO ◽

DOUGLAS GOUVÊA ◽

SHEILA L. VIEIRA

Keyword(s):

Shear Stress ◽

Shear Rate ◽

Electric Field ◽

Silicone Oil ◽

Ferroelectric Materials ◽

Dc Electric Field ◽

Ac Fields ◽

Er Fluid ◽

Constant Shear Rate

Electrorheology (ER) of ferroelectric materials such as nanometric BaTiO 3 is still not fully understood. In this paper, nanoparticles of Ba x Sr (1-x) TiO 3 (where x = 0.8, 0.9 or 1.0) were synthesized using the method of Pechini, calcinated at 950°C, and after, lixiviated under pH 1 or pH 5. A controlled stress rheometer (MCR-301) was used to make the ER characterization of dispersions made of Ba x Ti 1-x O 3 in silicone oil (30% w/w), where (a) shear stress as a function of DC electric field (under constant shear rate) or (b) shear stress as a function of shear rate (under constant AC or DC electric field) were measured. We observed that electrophoresis occurred under electric field DC, creating a concentration gradient which induced phase separation in ER fluid. On the other hand, under AC fields above 1 kV/mm, the ER effect is stronger than for DC field, and almost without electrophoresis. Furthermore, there is an AC frequency, dependent on the disperse phase, where the ER effect has a maximum.

Download Full-text

Analysis and Experimental Study on Rheological Performances of Magnetorheological Fluids

Mechanika ◽

10.5755/j01.mech.26.1.25244 ◽

2020 ◽

Vol 26 (1) ◽

pp. 31-34

Author(s):

Chao LIU ◽

Jianxin XIE ◽

Dongling CAI

Keyword(s):

Magnetic Field ◽

Experimental Study ◽

Shear Stress ◽

Shear Rate ◽

Volume Fraction ◽

Magnetorheological Fluids ◽

Bingham Model ◽

Shear Thinning Fluids ◽

Powder Rheometer ◽

Constant Shear Rate

Silicone-based Magnetorheological Fluids (MRFs) were prepared with 10% volume fraction of carbonyl iron powder. Rheometer Physica MCR 301 was used to test the rheological performances of MRFs.The experimental results show Bingham model and Casson model could well describe rheological behaviors of MRFs. Shear stress of MRFs increases but apparent viscosity is significantly decreased and tends to be stable with the increase of shear rate in the presence of magnetic field. The results also show that MRFs are shear thinning fluids. The dependence of shear stress on magnetic field was tested under the condition of constant shear rate and increasing magnetic field, shear stress of MRFs increases remarkably.

Download Full-text

Mechanical Properties of Paste Slurry under Constant Shear Rate in Initial Structure Failure Process

Advances in Materials Science and Engineering ◽

10.1155/2019/2971563 ◽

2019 ◽

Vol 2019 ◽

pp. 1-9

Author(s):

Chaoqun Dai ◽

Aixiang Wu ◽

Yan Qi ◽

Zhiqiang Chen ◽

Bin Li

Keyword(s):

Shear Stress ◽

Shear Rate ◽

Initial Stress ◽

Mass Concentration ◽

Model Equation ◽

Failure Process ◽

Initial Structure ◽

Structural Failure ◽

Constant Shear ◽

Constant Shear Rate

At constant shear rate, the process of deformation of the paste slurry is divided into two stages: one is the initial structural failure process with increasing shear stress; the other is the thixotropic process with decreasing shear stress after yielding. Based on experiments, the mechanical response characteristics of the paste slurry in the initial structural failure process under different shear rate conditions were studied in this paper. At the same time, according to the Maxwell model, the stress-time model equation describing the initial structure failure stage of the paste was deduced and the constant shearing test was carried out on the paste slurry at different mass concentrations; the model equation was used to fit the test data of the initial stress increment stage. The results showed that the model equation had higher prediction accuracy and better popularity. In the initial structural failure stage, the paste had a nonlinear stress-time relationship. At different shear rates (0.05, 0.5, and 1 s−1), the lower the rotation speed, the smoother the curve, and the slurry at various stages in the yielding process could be more clearly reflected; in the range of low constant shear rate (0.03, 0.05, and 0.07 s−1), the initial stress and yield stress of the paste increased with the increase of shear rate at the same mass concentration, and the time to yield was shorter. The yield stress increased exponentially with mass concentration.

Download Full-text

Double layers in the downward current region of the aurora

Nonlinear Processes in Geophysics ◽

10.5194/npg-10-45-2003 ◽

2003 ◽

Vol 10 (1/2) ◽

pp. 45-52 ◽

Cited By ~ 32

Author(s):

R. E. Ergun ◽

L. Andersson ◽

C. W. Carlson ◽

D. L. Newman ◽

M. V. Goldman

Keyword(s):

Magnetic Field ◽

Electron Beam ◽

Phase Space ◽

Electric Field ◽

Electric Fields ◽

Double Layers ◽

Parallel Electric Field ◽

Electrostatic Waves ◽

Current Region ◽

Decisive Evidence

Abstract. Direct observations of magnetic-field-aligned (parallel) electric fields in the downward current region of the aurora provide decisive evidence of naturally occurring double layers. We report measurements of parallel electric fields, electron fluxes and ion fluxes related to double layers that are responsible for particle acceleration. The observations suggest that parallel electric fields organize into a structure of three distinct, narrowly-confined regions along the magnetic field (B). In the "ramp" region, the measured parallel electric field forms a nearly-monotonic potential ramp that is localized to ~ 10 Debye lengths along B. The ramp is moving parallel to B at the ion acoustic speed (vs) and in the same direction as the accelerated electrons. On the high-potential side of the ramp, in the "beam" region, an unstable electron beam is seen for roughly another 10 Debye lengths along B. The electron beam is rapidly stabilized by intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. The "wave" region is physically separated from the ramp by the beam region. Numerical simulations reproduce a similar ramp structure, beam region, electrostatic turbulence region and plasma characteristics as seen in the observations. These results suggest that large double layers can account for the parallel electric field in the downward current region and that intense electrostatic turbulence rapidly stabilizes the accelerated electron distributions. These results also demonstrate that parallel electric fields are directly associated with the generation of large-amplitude electron phase-space holes and plasma waves.

Download Full-text

Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

Annales Geophysicae ◽

10.5194/angeo-34-55-2016 ◽

2016 ◽

Vol 34 (1) ◽

pp. 55-65 ◽

Cited By ~ 4

Author(s):

A. D. M. Walker ◽

G. J. Sofko

Keyword(s):

Magnetic Field ◽

Steady State ◽

Electric Field ◽

Electric Fields ◽

Magnetic Field Line ◽

Geomagnetic Field ◽

Geomagnetic Field Models ◽

Spatial Derivatives ◽

Field Lines ◽

The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

Download Full-text