Demonstration of Combined Shear and Squeeze Strengthening Modes in a Searle-Type Magnetorheometer

2013 ◽  
Author(s):  
Andrew C. Becnel ◽  
Norman M. Wereley
Keyword(s):  
Yield Stress ◽  
Energy Absorption ◽  
Shear Yield Stress ◽  
Particle Chain ◽  
Solids Loading ◽  
Mr Fluids ◽  
Shear Yield ◽  
Microstructure Model ◽  
Novel Method ◽  
A Chain

This research details a novel method of increasing the shear yield stress of magnetorheological (MR) fluids by combining shear and squeeze modes of operation to manipulate particle chain structures, to achieve so-called compression-assisted aggregation. The contribution of both active gap separation and particle concentration are experimentally measured using a custom-built Searle cell magnetorheometer, which is a model device emulating a rotary Magnetorheological Energy Absorber (MREA). Characterization data from large (1 mm) and small (250 μm) gap geometries are compared to investigate the effect of the gap on yield stress by compression enhancement. Two MR fluids having different particle concentrations (32 vol% and 40 vol%) are also characterized to demonstrate the effect of solids loading on compression-assisted chain aggregation. Details of the experimental setup and method are presented, and a chain microstructure model is used to explain experimental trends. The torque resisted by practical rotary MREAs is directly related to the strength of the MR fluid used, as measured by the shear yield stress. This study demonstrates that it is feasible, utilizing the compression-enhanced shear yield stress, to either (1) design a rotary MREA of a given volume to achieve higher energy absorption density (energy absorbed normalize by device volume), or (2) reduce the volume of a given rotary MREA to achieve the same energy absorption density.

Shear and Squeeze Rheometry of Magnetorheological Fluids

2011 ◽  
Vol 305 ◽  
pp. 344-347 ◽  
Author(s):  
Hong Yun Wang ◽  
Hui Qiang Zheng
Keyword(s):  
Magnetic Field ◽  
Yield Stress ◽  
Electrical Current ◽  
Test System ◽  
Compression Stress ◽  
Shear Yield Stress ◽  
Mr Fluid ◽  
Mr Fluids ◽  
Shear Yield ◽  
The Magnetic Field

The mechanical properties of a magnetorheological (MR) fluid in shearing, compression and shearing after compression have been studied in the magnetic field which is generated by a coil carrying different magnitudes of DC electrical current on a self-constructed test system. The relations of compression stress versus compression strain, yield stress versus compression stress were studied under different magnetic fields. The compressing tests showed that the MR fluid is very stiff at small compressive strains lower than 0.13. The shear yield stress of MR fluids after compression was much stronger than that of uncompressed MR fluids under the same magnetic field. The enhanced shear yield stress of MR fluids can be utilized to design the MR clutch and brake for new structure and will make MR fluids technology attractive for many applications.

Field-On Versus Field-Off Characteristics of Magnetorheological Fluids With an Application in Prosthetic Devices

2011 ◽  
Author(s):  
Ketill H. Gudmundsson ◽  
Fjola Jonsdottir ◽  
Freygardur Thorsteinsson
Keyword(s):  
Knee Joint ◽  
Yield Stress ◽  
Solid Loading ◽  
Fluid Composition ◽  
Shear Yield Stress ◽  
Mr Fluid ◽  
Prosthetic Devices ◽  
Prosthetic Knee ◽  
Mr Fluids ◽  
Shear Yield

The study presents an experimental investigation into the trade-offs between field-on versus field-off rheological characteristics of magnetorheological (MR) fluids. This is relevant in a particular application in prosthetic devices where field-off characteristics are of equal importance to the field-on rheological characteristics. The paper introduces a biomechanical prosthetic knee joint that uses an MR fluid to actively control its rotary stiffness while an amputee walks. The knee is a synergy of artificial intelligence, advanced sensors and MR actuator technology. The knee joint is equipped with an MR rotary brake, utilizing the fluid in direct-shear mode. The MR fluid has response time in the order of milliseconds, making it possible to vary the knee’s stiffness in real-time, depending on sensors data. The field-on characteristics of the employed MR fluid define the rigidness of the knee joint while the field-off characteristics define its flexibility in the absence of a magnetic field. Five MR fluid compositions are prepared, each with a different solid loading ranging from 0.25 to 0.35, by volume. All fluids employ a commercially available carbonyl iron powder and a base fluid. The MR fluids are experimentally evaluated in a rheometer, where both field-off and field-on characteristics are measured. An MR fluid figure of merit function is introduced which is used to rate the selected MR fluids for a potential application in the MR prosthetic knee. An MR fluid composition is sought with the highest ratio between the field-on shear yield stress and the off-state viscosity. The research shows the off-state viscosity to decrease faster than the field-on shear yield stress when reducing the solid loading from 0.35 to 0.25. This suggests that an optimum solid loading exists with regards to the defined merit function. The off-state viscosity of suspensions is known to be exponentially dependent on solid loading while the field-on shear-yield stress is known to sub-quadratically dependent on solid loading. Field-on and field-off models are presented from literature. The models compared to the experimental data and used to theoretically predict the optimum solid loading with regards to field-on shear yield stress and off-state viscosity. As a result of the experimental and the theoretical analysis, a prominent MR fluid composition is selected for a potential application in the MR prosthetic knee. This has been shown to help in the development of prosthetic devices and furthering the success of an MR prosthetic knee joint.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

2020 ◽  
Vol 35 (2) ◽  
pp. 243-250
Author(s):  
Jiulong Sha ◽  
Yueyue Yang ◽  
Can Wang ◽  
Wei Li ◽  
Peng Lu ◽  
...  
Keyword(s):  
Yield Stress ◽  
Paper Industry ◽  
Pulp Fiber ◽  
Fiber Suspensions ◽  
Fiber Morphology ◽  
Shear Yield Stress ◽  
Geometrical Properties ◽  
Compressive Yield Stress ◽  
Shear Yield ◽  
Fiber Cell Wall

AbstractThe degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress {P_{y}} and shear yield stress {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of {\tau _{y}}/{P_{y}} were also examined and the variation of {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

Shear yield stress of partially flocculated colloidal suspensions

AIChE Journal ◽  
1998 ◽  
Vol 44 (3) ◽  
pp. 538-544 ◽  
Author(s):  
Peter J. Scales ◽  
Stephen B. Johnson ◽  
Thomas W. Healy ◽  
Prakash C. Kapur
Keyword(s):  
Yield Stress ◽  
Colloidal Suspensions ◽  
Shear Yield Stress ◽  
Shear Yield

Compression Enhanced Shear Yield Stress of Electrorheological Fluid

2009 ◽  
Vol 26 (4) ◽  
pp. 048301 ◽  
Author(s):  
Zhang Min-Liang ◽  
Tian Yu ◽  
Jiang Ji-Le ◽  
Zhu Xu-Li ◽  
Meng Yong-Gang ◽  
...  
Keyword(s):  
Yield Stress ◽  
Electrorheological Fluid ◽  
Shear Yield Stress ◽  
Shear Yield

Effect of annealing on the shear yield stress of rejuvenated polycarbonate

Polymer ◽  
1988 ◽  
Vol 29 (11) ◽  
pp. 1985-1989 ◽  
Author(s):  
C. Bauwens-Crowet ◽  
J-C. Bauwens
Keyword(s):  
Yield Stress ◽  
Shear Yield Stress ◽  
Shear Yield

scholarly journals Preliminary experimental evaluation of a novel loudspeaker featuring magnetorheological fluid surround absorber

2020 ◽  
Vol 17 (2) ◽  
pp. 922 ◽  
Author(s):  
Endra Dwi Purnomo ◽  
Ubaidillah Ubaidillah ◽  
Fitrian Imaduddin ◽  
Iwan Yahya ◽  
Saiful Amri Mazlan
Keyword(s):  
Magnetic Flux ◽  
Yield Stress ◽  
Experimental Evaluation ◽  
Flux Distribution ◽  
Magnetic Circuit ◽  
Experimental Result ◽  
The Finite Element Method ◽  
Shear Yield Stress ◽  
Shear Yield ◽  
Novel Design

<span>A novel design of magnetorheological fluids (MRF) based surround device in a loudspeaker system was studied in this article. The main objective of this research is to design a new surround device of the loudspeaker that can be easily controlled its damping. Therefore, it was predicted that the audio pressure level on the loudspeaker could be easily manipulated at a different sound source by applying a certain magnetic field. This function could not be reached using one conventional speaker system. Firstly, a set of an electromagnetic device containing MRF was designed to replace the conventional rubber surround. The magnetic circuit was then evaluated using the finite element method magnetics to study the flux distribution in the MRF area. The current was varied from 0.25 to 0.75 A by an interval of 0.25 A. The magnetic flux resulted from the simulation was then logged and used as the based value for predicting the change of shear yield stress. The base properties of the shear yield stress of the MRF against the magnetic flux was obtained from previous experimental result. Therefore, it was hopefully the prediction could be closed to the real system. Based on the simulation result, the shear yield stress varied from 43 to 49 Mpa or about 15 % increment. </span><span lang="IN">A simple experimental work was carried out. By applying particular direct current into the coil, the sound quality generated by the loudspeaker shows different values</span><span>.</span><span lang="IN"> Based on the preliminary experiment, the level of decibel decreased about 3 dB as the application of magnetic fields. The idea has been proven in this preliminary experimental evaluation.</span>

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