Trends in acoustic properties of iron particle seeded auxetic polyurethane foam

2004 ◽  
Vol 218 (2) ◽  
pp. 241-244 ◽  
Author(s):  
F Scarpa ◽  
W A Bullough ◽  
P Lumley
Keyword(s):  
Magnetic Fields ◽  
Iron Particle ◽  
Magnetorheological Fluid ◽  
Acoustic Properties ◽  
Absorption Characteristic ◽  
Frequency Bandwidth ◽  
Iron Particles ◽  
Constant Intensity ◽  
Acoustic Absorption Coefficient ◽  
Flexible Foam

The sound absorption characteristic of a clean, open-cell configuration, typical polyurethane flexible foam is shown against that of an auxetic foam made from it, and this same foam after it has been seeded with a magnetorheological fluid (then dried), having 2–5 μm carbonyl iron particles and subjected to zero, weak and concentrated magnetic fields in an acoustic impedance tube facility. The resultant foam indicates the capability of shifting the peak acoustic absorption coefficient within a given frequency bandwidth when constant intensity magnetic fields are applied.

Acoustic Properties of Auxetic Foams With MR Fluids

2003 ◽  
Author(s):  
F. Scarpa ◽  
W. A. Bullough ◽  
M. Ruzzene
Keyword(s):  
Low Frequency ◽  
Acoustic Properties ◽  
Acoustic Absorption ◽  
Frequency Bandwidth ◽  
Frequency Range ◽  
Absorption Properties ◽  
Open Cell ◽  
Mr Fluids ◽  
Acoustic Absorption Coefficient ◽  
Open Cell Foams

This paper presents an experimental investigation on the acoustic properties of novel concepts of auxetic (Negative Poisson’s ratio) open cell polyurethane gray foams. The acoustic absorption coefficients and real and imaginary part of the specific acoustic impedance for the considered foams are measured with an ASTM standard impedance tube using a transmissibility technique. The auxetic foams show a significant increase of the absorption properties in the low frequency range compared to equivalent conventional open cell foams. Their acoustic properties are identified using an empirical model to describe the main structural characteristic. In addition, measurements for auxetic foams seeded with a magnetorheological fluid are also presented. The results show the capability of the seeded foam of shifting the peak acoustic absorption coefficient within a given frequency bandwidth when concentrated magnetic fields are applied.

Influence of Permanent Magnets Installation Approach on the Torque of а Magneto-Rheological Disk Brake

2021 ◽  
Vol 105 ◽  
pp. 184-193
Author(s):  
Ilya Aleksandrovich Frolov ◽  
Andrei Aleksandrovich Vorotnikov ◽  
Semyon Viktorovich Bushuev ◽  
Elena Alekseevna Melnichenko ◽  
Yuri Viktorovich Poduraev
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Materials ◽  
Permanent Magnets ◽  
Magnetorheological Fluid ◽  
Simulation Modelling ◽  
Disc Brake ◽  
Large Area ◽  
Braking Torque ◽  
The Magnetic Field

Magnetorheological braking devices function due to the organization of domain structures between liquid and solid magnetic materials under the action of an electromagnetic or magnetic field. The disc is most widely used as a rotating braking element that made of a solid magnetic material due to the large area of contact with a magnetorheological fluid. Many factors affect the braking characteristics of the magnetorheological disc brake. Specifically, the value of the magnetic field and how the field is distributed across the work element is significantly affected at the braking torque. There are different ways to generate a magnetic field. In this study, the method of installation of permanent magnets into the construction, allowing to increase the braking torque of the magnetorheological disc brake is proposed. Simulation modelling showing the distribution of the magnetic field across the disk depending on the installation of permanent magnets with different pole orientations were carried out. The model takes into account the possibility of increasing the gap between solid magnetic materials of the structure, inside them which the magnetorheological fluid is placed. Comparative estimation of the distribution of the magnetic fields depending on the chosen method of installation of permanent magnets with different orientations of their poles is carried out. Further research is planned to focus on a comparative assessment of the distribution of magnetic fields depending on the selected material of the braking chamber.

Acoustic Properties of Materials for Vibration Reduction and Resistance on Ultra-Precision Machine

2014 ◽  
Vol 620 ◽  
pp. 140-145
Author(s):  
Dan Huang ◽  
Ying Wang
Keyword(s):  
Absorption Coefficient ◽  
Porous Ceramic ◽  
Vibration Reduction ◽  
Calculation Model ◽  
Acoustic Energy ◽  
Acoustic Properties ◽  
Acoustic Absorption ◽  
Cylindrical Pore ◽  
Acoustic Absorption Coefficient ◽  
Ultra Precision

The porous ceramic holds good potential as acoustic resistance and vibration reduction material during ultra-precision machining. Porous materials absorb acoustic energy by friction with the air that moves inside the pores, and in this paper, the motion is simplified as the incompressible fluid in a single cylindrical pore. The analysis and calculation results show that the acoustic coefficient of porous ceramic is a complicated wave function and the acoustic absorption coefficient calculation model is feasible based on fluid thermal viscous theory. The acoustic absorption coefficient of porous ceramic increases with the increase of thickness, and its period and amplitude decreases with the increase of porosity of ceramic.

Zirconia-coated carbonyl-iron-particle-based magnetorheological fluid for polishing optical glasses and ceramics

2009 ◽  
Vol 48 (35) ◽  
pp. 6797 ◽  
Author(s):  
Shai N. Shafrir ◽  
Henry J. Romanofsky ◽  
Michael Skarlinski ◽  
Mimi Wang ◽  
Chunlin Miao ◽  
...  
Keyword(s):  
Carbonyl Iron ◽  
Iron Particle ◽  
Magnetorheological Fluid ◽  
Optical Glasses ◽  
Carbonyl Iron Particle

Fabrication and characterization of highly controllable magnetorheological material in compression mode

2020 ◽  
Vol 31 (14) ◽  
pp. 1641-1661 ◽  
Author(s):  
Amin Fereidooni ◽  
Afonso Martins ◽  
Viresh Wickramasinghe ◽  
Afzal Suleman
Keyword(s):  
Magnetic Fields ◽  
Loss Factor ◽  
Magnetorheological Fluid ◽  
Loading Frequency ◽  
Magnetorheological Elastomer ◽  
Magnetorheological Elastomers ◽  
Equivalent Damping ◽  
Magnetorheological Effect ◽  
Equivalent Damping Coefficient

This article is focused on the development and characterization of highly controllable magnetorheological materials for stiffness and damping control in semi-active control applications. Two types of magnetorheological materials are developed in-house: magnetorheological elastomer with soft base elastomer, and magnetorheological fluid encapsulated in regular elastomer, namely magnetorheological fluid-elastomer. In both cases of magnetorheological elastomers and magnetorheological fluid-elastomers, the samples are evaluated using in-house-developed shear and compression test rigs, which are equipped with electromagnets and Hall effect sensors for measuring the magnetic field. These features provide the capability to precisely control a wide range of magnetic fields during the experiments. In the case of magnetorheological elastomers, the experimental results of the in-house magnetorheological elastomers are compared with commercially available counterparts made of hard base elastomer. It is shown that the controllability of the material, that is, the relative magnetorheological effect, is significantly improved in the case of magnetorheological elastomer with soft base elastomer. In addition to various magnetic fields, the samples are subjected to a range of loading amplitudes and frequencies. A general trend is observed where the frequency and strain amplitude cause an opposite effect on both the shear and compressive moduli: the increase in frequency gives rise to a higher value of modulus whereas the increase in amplitude reduces the modulus. Furthermore, the effect of bonding on the performance of the magnetorheological elastomers in compression mode is evaluated and the results indicate a significant increase in the modulus and decrease in the loss factor. In all the cases, however, the change of loss factor does not exhibit a predictable trend as a function of magnetic fields. In order to investigate a magnetorheological-based solution for controlling the damping of a semi-active system, magnetorheological fluid-elastomer samples are made in-house. These samples are fabricated using three different iron concentrations, and are tested in compression (squeeze) mode. The results of these experiments confirm that the equivalent damping coefficient of the material rises with the increase in magnetic field, and this effect becomes stronger as the iron concentration of magnetorheological fluids increases. It is also demonstrated that the magnetorheological effect is highly dependent on the loading frequency and amplitude, where the equivalent damping coefficient decreases with the increase in loading frequency and amplitude. In all the aforementioned cases, the stiffness of magnetorheological fluid-elastomers exhibits minor changes, which offers the in-house-developed magnetorheological fluid-elastomers as a damping only control option, a development that is different from the magnetorheological fluid-elastomers reported in the literature.

Influence of Different Gradation Carbonyl Iron Particles on the Properties of Magneto-Rheological Fluids

2012 ◽  
Vol 452-453 ◽  
pp. 623-627
Author(s):  
Cheng Bin Du ◽  
Guo Jun Yu ◽  
Zhi Wei Gong
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Shear Stress ◽  
Single Particle ◽  
Carbonyl Iron ◽  
Iron Particle ◽  
Iron Particles ◽  
Carbonyl Iron Particle ◽  
Magneto Rheological ◽  
Multiple Particle

The influence of carbonyl iron particles sizes on the properties of magneto-rheological fluids (MRFs) were studied. Different-sized carbonyl iron magnetic particles were prepared by ball milling with different milling times. On this basis, different particle MRF were prepared The off-state viscosity and the shear stress of the above MRFs were characterised and studied by an advanced rotational rheometer system. The test results show that the off-state viscosity and the shear stress of single-particle MRFs were enhanced with increasing average carbonyl iron particle size at a constant magnetic field. The shear stresses of MRFs containing two or three different particle sizes were significantly improved compared with the MRFs containing only a single particle size. At a reasonable level of medium and small size carbonyl iron particle spread throughout the structure of the multiple-particle MRFs, the defects in the chain structure were remedied when a chain reaction occurred, and the mechanical properties of MRFs were enhanced. Meanwhile, increased mass fractions of the small size carbonyl iron particle resulted in a reduction in overall average particle size of MRFs, and the mechanical properties of MRFs were also reduced. The mechanical properties of multiple-particle MRFs were observed to be strongly dependent on the size and mass fraction of the medium and small carbonyl iron particles.

scholarly journals Frequency-dependent variation in the two-dimensional beam pattern of an echolocating dolphin

2011 ◽  
Vol 7 (6) ◽  
pp. 836-839 ◽  
Author(s):  
Josefin Starkhammar ◽  
Patrick W. Moore ◽  
Lois Talmadge ◽  
Dorian S. Houser
Keyword(s):  
Sound Propagation ◽  
Sound Field ◽  
Spatial Separation ◽  
Acoustic Properties ◽  
Maximum Pressure ◽  
Frequency Bandwidth ◽  
Sound Sources ◽  
Pressure Peak ◽  
Prey Localization ◽  
Dominant Peak

Recent recordings of dolphin echolocation using a dense array of hydrophones suggest that the echolocation beam is dynamic and can at times consist of a single dominant peak, while at other times it consists of forward projected primary and secondary peaks with similar energy, partially overlapping in space and frequency bandwidth. The spatial separation of the peaks provides an area in front of the dolphin, where the spectral magnitude slopes drop off quickly for certain frequency bands. This region is potentially used to optimize prey localization by directing the maximum pressure slope of the echolocation beam at the target, rather than the maximum pressure peak. The dolphin was able to steer the beam horizontally to a greater extent than previously described. The complex and dynamic sound field generated by the echolocating dolphin may be due to the use of two sets of phonic lips as sound sources, or an unknown complexity in the sound propagation paths or acoustic properties of the forehead tissues of the dolphin.

NANOSTRUCTURED AND SURFACE POLYMERIZED IRON PARTICLES FOR MAGNETORHEOLOGICAL FLUIDS

2007 ◽  
Vol 21 (28n29) ◽  
pp. 4819-4824 ◽  
Author(s):  
BEN HU ◽  
ALAN FUCHS ◽  
FARAMARZ GORDANINEJAD ◽  
CAHIT EVRENSEL
Keyword(s):  
Butyl Acrylate ◽  
Magnetorheological Fluid ◽  
Molar Ratio ◽  
Iron Particles ◽  
Scanning Calorimetry ◽  
Kissinger’S Method ◽  
Shear Yield ◽  
Coating Procedure ◽  
Dsc Method ◽  
Kinetics Of

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly (butyl acrylate) by surface initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-4(-chlorosulfonylphenyl)-ethytrichlorosilane (CTCS) on the iron particles surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles surface by ATRP can significantly reduce iron particles settling and improve stability of the MR fluid. Polymerization kinetics of bulk butyl acrylate are investigated using differential scanning calorimetry (DSC). Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of In ( M / M 0) against polymerization time. The overall activation energy is found to be 126kJ/mol by Kissinger's Method.

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