HIGH VERSUS LOW FIELD VISCOMETRIC CHARACTERIZATION OF BIDISPERSE MR FLUIDS

2007 ◽  
Vol 21 (28n29) ◽  
pp. 4922-4928 ◽  
Author(s):  
G. T. NGATU ◽  
N. M. WERELEY
Keyword(s):  
Magnetic Field ◽  
Yield Stress ◽  
High Field ◽  
Magnetic Flux Density ◽  
Flow Curves ◽  
Bingham Plastic ◽  
Low Field ◽  
Mr Fluids ◽  
Low Magnetic Field

Our bidisperse magnetorheological fluids are suspensions of micron (2-10μm) and nanometer (~40nm) scale magnetic iron particles in silicone or hydraulic oil. Earlier studies were conducted to determine the yield stress of these fluids at low magnetic field induction. These studies have shown the absence of saturation yield stress implying the possibility of a higher yield stress by increasing the applied field. In this study, three different bidisperse MR fluids were investigated to determine the maximum available yield stress that can be obtained at or near saturation magnetic flux density. The iron loading in the fluids varied from 50% to 80% by weight. Two types of MR cells, a low field and a high field cells, were used for the investigation. Using a parallel disc rheometer alternatively equipped with one of the two MR cells, the flow curves of the MR fluids were obtained and their yield stress determined. The yield stress of the MR fluids as a function of applied magnetic field was identified using the Bingham-Plastic constitutive model. Results show that the high field cell (maximum 1 Tesla) was able to measure shear stress up to saturation, whereas the low field cell (maximum 0.26 Tesla) could not.

Testing of a Dual Field Magnetic Flux Leakage (MFL) Inspection Tool for Detecting and Characterizing Mechanical Damage Features

2008 ◽  
Author(s):  
Alex Rubinshteyn ◽  
Steffen Paeper ◽  
Bruce Nestleroth
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Residual Stresses ◽  
High Field ◽  
Mechanical Damage ◽  
Magnetic Flux Leakage ◽  
Low Field ◽  
Field Unit ◽  
Low Magnetic Field ◽  
Flux Leakage

Battelle has developed dual field magnetic flux leakage (MFL) technology for the detection and characterization of mechanical damage to pipelines. The basic principle involves the use of a high magnetic field between 140 and 180 Oersted (11.1 to 14.3 kA/m) and the use of a low magnetic field between 50 and 70 Oersted (4 to 5.6 kA/m). At high magnetic field levels, the flux leakage signal is primarily influenced by changes in the geometry of a pipe wall. At low magnetic field levels, the MFL signal is due to residual stresses and metallurgical changes as well as geometry changes to the pipe caused by mechanical damage and wall thinning. A decoupling signal processing method developed by Battelle is used to isolate the portion of the mechanical damage signals due to metallurgical damage and residual stresses, which allows the characteristics of a dent-gouge feature to be more clearly differentiated. The decoupling method involves first scaling down the high field signal to the level of the low field signal, and then subtracting it from the low field signal. This produces a decoupled signal that is primarily influenced by the residual stresses and metallurgical changes caused by mechanical damage. Rosen has developed a tool to test the dual field technology and is evaluating tool performance by running the tool in a 30 inch diameter pipeline segment. The tool itself is composed of three separate modules coupled together: a high field unit downstream of a low field unit which is downstream of a caliper arm unit that is used to detect and characterize reductions in the internal diameter. The general and magnetic design of the tool, along with the scaling algorithm is discussed. Results from a pull test in a pipe section with dents whose geometry has been independently characterized are also discussed. This work is partially funded by the U.S. Department of Transportation, Pipeline and Hazardous Materials Safety administration (DOT PHMSA) and the Pipeline Research Council International, Inc. (PRCI).

Yield and Rheological Behaviors of Magnetorheological Fluids

2010 ◽  
Vol 97-101 ◽  
pp. 875-879
Author(s):  
Jian Min He ◽  
Jin Huang ◽  
Cheng Liu
Keyword(s):  
Magnetic Field ◽  
Yield Stress ◽  
Applied Magnetic Field ◽  
Applied Field ◽  
Shear Strain Rate ◽  
Bingham Model ◽  
Bingham Plastic ◽  
Rheological Behaviors ◽  
Mr Fluids ◽  
Magnetic Chain

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with the change of their yield and rheological behaviors. In this paper, the yield and rheological behaviors of MR fluids are discussed. Based on the microstructure of magnetic chain a theoretical model is developed to analyze the effect of an applied magnetic field on the yield stress of MR fluids. Bingham model is used to describe the rheological behaviors of MR fluids subject to an applied magnetic field. The results show that altering the strength of an applied field can control the yield stress of MR fluids. The shear stress increases as the strength of an applied magnetic field increases, and it hardly changes with the increase of shear strain rate. MR fluids exhibit Bingham plastic model.

Compression Resistance of Magnetorheological Fluid

2010 ◽  
Vol 143-144 ◽  
pp. 624-628 ◽  
Author(s):  
Hong Yun Wang ◽  
Xiao Wang ◽  
Cheng Bi
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Yield Stress ◽  
Flux Density ◽  
Magnetic Flux Density ◽  
Compression Stress ◽  
Mr Fluids ◽  
Shear Yield ◽  
Compression Characteristics ◽  
Compression Resistance

The ability of magnetorheological(MR) fluids to resist compression in the direction of magnetic field was tested to investigate the quasi-static squeezing process of MR fluids. A experiment setup was designed and fabricated to test the compression characteristics. Under the different magnetic flux density, the curves of the MR fluids were studied for yield stress versus compression stress, compression stress versus compression strain. The compression resistance of MRF was then measured for the different magnetic flux density for comparison with the shear yield strength of the same magnetic field. The results showed that the compression resistance of the MRF was much stronger than its shear yield stress for the same magnetic field strength conditions. The compression resistance of MRF can be utilized to design new magnetorheological devices.

Mathematical Modelling and Design and of MR Dampers

Volume 2 ◽  
2004 ◽  
Author(s):  
Weng W. Chooi ◽  
S. Olutunde Oyadiji
Keyword(s):  
Magnetic Field ◽  
Yield Stress ◽  
Active Vibration Control ◽  
Mr Fluid ◽  
Bingham Plastic ◽  
Mr Dampers ◽  
Mr Fluids ◽  
Annular Gap ◽  
Active Valve ◽  
Active Vibration

Most magnetorheological (MR) fluid devices are fixed-pole valve mode devices where the fluid flows through a magnetically active valve. Controlling the strength of the magnetic field inside the valve allows the rheological properties of the MR fluid to be varied. Upon the application of a magnetic field, MR fluids develop a yield stress, which must be overcome before any flow is possible. This behavior can be represented mathematically by models of fluid with a yield stress like the Bingham plastic model. MR dampers have utilized this property of the MR fluids to provide controllable, semi-active vibration control. The most effective and widely used configuration of MR dampers incorporates an annular gap through which the MR fluid is force to flow. This paper presents a solution for annulus flows, derived from fundamental equations of fluid mechanics, of any general model of fluid with a yield stress. An example of the application of the general analytical expressions using the Herschel-Buckley model is given, and the limitations of the parallel plate approximation is illustrated for configurations whereby the size of the annular gap relative to the mean radius is large. Finally, the flow solution is incorporated into the mathematical model of an MR damper designed at the University of Manchester, and simulation results incorporating the effects of compressibility in the modeling procedure are presented. It was shown that this model can describe the major characteristics of such a device — nonlinear, asymmetric and hysteretic behaviors — successfully.

EVALUATIONS OF CLUSTER STRUCTURE AND MAGNETO-RHEOLOGY OF MR SUSPENSIONS

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1437-1442 ◽  
Author(s):  
HIDEYA NISHIYAMA ◽  
KAZUNARI KATAGIRI ◽  
KATSUHISA HAMADA ◽  
KAZUTO KIKUCHI ◽  
KATSUHIKO HATA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cluster Formation ◽  
Cluster Structure ◽  
Mr Damper ◽  
Magnetic Flux Density ◽  
Equivalent Damping ◽  
Damping Characteristics ◽  
Mr Fluids ◽  
Equivalent Damping Coefficient ◽  
Particle Shapes

In the present study, we sysnthesize two types of MR fluids with different particle shapes and sizes. The magnetic functions are evaluated circulatingly by the analysis of cluster formation, rheological properties in the applied magnetic field and damping characteristics in the MR damper, comparing with those of commercial MR fluids. Final objective is to provide the fundamental data for the development of newly advanced MR fluids. The main topics consist of geographycal cluster formation depending on particle shapes and sizes, relating to the apparent viscosity and yield stress with magnetic flux density and further equivalent damping coefficient of two newly sysnthesised MR fluids comparing with those of LORD MR fluid.

Platform Design for Characterizing Shear Force Produced by Magnetized Magnetorheological Fluid

2019 ◽  
Author(s):  
Ping-Hsun Lee ◽  
Jen-Yuan (James) Chang
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Yield Stress ◽  
Flux Density ◽  
Shear Force ◽  
Permanent Magnets ◽  
Magnetic Flux Density ◽  
Finite Element Method Result ◽  
Mr Fluid ◽  
The Magnetic Field

Abstract In this paper we proposed a platform for measuring shear force of magnetorheological (MR) fluid by which the relationship of yield stress and magnetic flux density of specific material can be determined. The device consisted of a rotatable center tube in a frame body and the magnetic field was provided by two blocks of permanent magnets placed oppositely outside the frame body. The magnitude and direction of the magnetic field were manipulated by changing the distance of the two permanent magnets from the frame body and rotating the center tube, respectively. For determining the magnetic field of the device, we adopted an effective method by fitting the FEM (finite element method) result to the measured one and then rebuilt the absent components to approximate the magnetic field, which was hardly to be measured simultaneously as different device setup were required. With the proposed platform and analytical methods, the drawing shear force and the corresponding yield stress contributed by MR fluid could be evaluated in respect to the magnitude and direction of given magnetic flux density with acceptable accuracy for specific designing purposes without a large, complex, and expensive instrument.

MAGNETORHEOLOGICAL FLUIDS AND THEIR PROPERTIES

2005 ◽  
Vol 19 (01n03) ◽  
pp. 593-596 ◽  
Author(s):  
J. M. HE ◽  
J. HUANG
Keyword(s):  
Magnetic Field ◽  
Yield Strength ◽  
Rheological Properties ◽  
Yield Stress ◽  
Applied Magnetic Field ◽  
Magnetorheological Fluids ◽  
Mr Fluid ◽  
Variable Yield ◽  
Mr Fluids

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological properties. Upon application of a magnetic field, MR fluids have a variable yield strength. Altering the strength of the applied magnetic field will control the yield stress of these fluids. In this paper, the method for measuring the yield stress of MR fluids is proposed. The curves between the yield stress of the MR fluid and the applied magnetic field are obtained from the experiment. The result indicates that with the increase of the applied magnetic field the yield stress of the MR fluids goes up rapidly.

scholarly journals Characterization of unsaturated porous media by high-field and low-field NMR relaxometry

2009 ◽  
Vol 45 (8) ◽  
Author(s):  
L. R. Stingaciu ◽  
A. Pohlmeier ◽  
P. Blümler ◽  
L. Weihermüller ◽  
D. van Dusschoten ◽  
...  
Keyword(s):  
Porous Media ◽  
High Field ◽  
Unsaturated Porous Media ◽  
Low Field ◽  
Nmr Relaxometry ◽  
Low Field Nmr

scholarly journals Comparison of Pr-doped Ca 122 and Ca 112 Pnictides by Low-field Microwave Absorption Spectroscopy

2014 ◽  
Vol 1684 ◽  
Author(s):  
Austin R. Howard ◽  
Jonathan D. Yuen ◽  
Bing Lv ◽  
Myron Salamon ◽  
Ching-Wu Chu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Microwave Absorption ◽  
Absorption Spectroscopy ◽  
Superconducting State ◽  
Superconducting Phase ◽  
Interfacial Phase ◽  
Low Field ◽  
Low Magnetic Field ◽  
Anisotropic Magnetization

ABSTRACTPraseodymium doped CaFe2As2 (122 structure) and CaFeAs2 (112 structure) are characterized by modulated Low Magnetic Field Microwave Absorption (LFMA) spectroscopy. In both (Pr,Ca)122 and (Pr,Ca)112 structures, a strong hysteretic LFMA is found, with a TcH of ∼30 K and ∼26 K, respectively. However, in (Pr,Ca)122, measurements also show an unusual Narrow Peak (NP) LFMA signal appearing at higher temperatures, above the lower TcH superconducting state until a TcNP of 49 K. We associate this NP LFMA with interfacial superconductivity, which has been found previously by highly anisotropic magnetization measurements. Furthermore, the absence of NP in (Pr,Ca)112 correlates with the absence of an interfacial phase. These results give useful information about the microwave signature of interfacial superconductivity present in the (Pr,Ca)122 system, and may form a roadmap towards a stabilized high temperature superconducting phase in pnictides.

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