Abstract:Elastic percolation transition in nanowire-based magnetorheological fluids Appl. Phys. Lett. 95, 014102 (2009); 10.1063/1.3167815 Dynamic yield stress enhancement in bidisperse magnetorheological fluids J. Rheol. 49, 1521 (2005); 10.1122/1.2085175Study on the mechanism of the squeeze-strengthen effect in magnetorheological fluids
“…15) when a force of approximately 30 N obtained at 0 A is increased to 122 N, 160 N, and 240 N under 1.4 A excitation for the squeeze, shear-flow, and mixed modes, respectively. Again, this fluid performance enhancement under mixed mode operation is in agreement with those reported by Sarkar and Hirani [27], Spaggiari and Dragoni [28] and Becnel et al [29] although the shearing of the fluid in their mixed squeeze-shear cells was achieved through piston rotations rather than through a direct axial motion which is realized in this investigation.…”
Section: Resultssupporting
confidence: 93%
“…Again, this fluid performance enhancement under mixed mode operation is in agreement with those reported by Sarkar and Hirani, 27 Spaggiari and Dragoni 28 and Becnel et al. 29 although the shearing of the fluid in their mixed squeeze-shear cells was achieved through piston rotations rather than through a direct axial motion which is realised in this investigation. Figure 12.Variation of transmitted force with time for single and mixed modes under oscillatory motion.Figure 13.Variation of transmitted force with displacement for single and mixed modes under oscillatory motion.Figure 14.Variation of transmitted force with velocity for single and mixed modes under oscillatory motion.Figure 15.Variation of yield force with current for MR fluid under single and mixed modes.…”
Rheological properties of magnetorheological (MR) fluids can be changed by application of external magnetic fields. These dramatic and reversible field-induced rheological changes permit the construction of many novel electromechanical devices having potential utility in the automotive, aerospace, medical and other fields. Vibration control is regarded as one of the most successful engineering applications of magnetorheological devices, most of which have exploited the variable shear, flow or squeeze characteristics of magnetorheological fluids. These fluids may have even greater potential for applications in vibration control if utilised under a mixed-mode operation. This article presents results of an experimental investigation conducted using magnetorheological fluids operated under dynamic squeeze, shear-flow and mixed modes. A special magnetorheological fluid cell comprising a cylinder, which served as a reservoir for the fluid, and a piston was designed and tested under constant input displacement using a high-strength tensile machine for various magnetic field intensities. Under vertical piston motions, the magnetorheological fluid sandwiched between the parallel circular planes of the cell was subjected to compressive and tensile stresses, whereas the fluid contained within the annular gap was subjected to shear flow stresses. The magnetic field required to energise the fluid was provided by a pair of toroidally shaped coils, located symmetrically about the centerline of the piston and cylinder. This arrangement allows individual and simultaneous control of the fluid contained in the circular and cylindrical fluid gaps; consequently, the squeeze mode, shear-flow mode or mixed-mode operation of the fluid could be activated separately. The performance of these fluids was found to depend on the strain direction. Additionally, the level of transmitted force was found to improve significantly under mixed-mode operation of the fluid.
“…15) when a force of approximately 30 N obtained at 0 A is increased to 122 N, 160 N, and 240 N under 1.4 A excitation for the squeeze, shear-flow, and mixed modes, respectively. Again, this fluid performance enhancement under mixed mode operation is in agreement with those reported by Sarkar and Hirani [27], Spaggiari and Dragoni [28] and Becnel et al [29] although the shearing of the fluid in their mixed squeeze-shear cells was achieved through piston rotations rather than through a direct axial motion which is realized in this investigation.…”
Section: Resultssupporting
confidence: 93%
“…Again, this fluid performance enhancement under mixed mode operation is in agreement with those reported by Sarkar and Hirani, 27 Spaggiari and Dragoni 28 and Becnel et al. 29 although the shearing of the fluid in their mixed squeeze-shear cells was achieved through piston rotations rather than through a direct axial motion which is realised in this investigation. Figure 12.Variation of transmitted force with time for single and mixed modes under oscillatory motion.Figure 13.Variation of transmitted force with displacement for single and mixed modes under oscillatory motion.Figure 14.Variation of transmitted force with velocity for single and mixed modes under oscillatory motion.Figure 15.Variation of yield force with current for MR fluid under single and mixed modes.…”
Rheological properties of magnetorheological (MR) fluids can be changed by application of external magnetic fields. These dramatic and reversible field-induced rheological changes permit the construction of many novel electromechanical devices having potential utility in the automotive, aerospace, medical and other fields. Vibration control is regarded as one of the most successful engineering applications of magnetorheological devices, most of which have exploited the variable shear, flow or squeeze characteristics of magnetorheological fluids. These fluids may have even greater potential for applications in vibration control if utilised under a mixed-mode operation. This article presents results of an experimental investigation conducted using magnetorheological fluids operated under dynamic squeeze, shear-flow and mixed modes. A special magnetorheological fluid cell comprising a cylinder, which served as a reservoir for the fluid, and a piston was designed and tested under constant input displacement using a high-strength tensile machine for various magnetic field intensities. Under vertical piston motions, the magnetorheological fluid sandwiched between the parallel circular planes of the cell was subjected to compressive and tensile stresses, whereas the fluid contained within the annular gap was subjected to shear flow stresses. The magnetic field required to energise the fluid was provided by a pair of toroidally shaped coils, located symmetrically about the centerline of the piston and cylinder. This arrangement allows individual and simultaneous control of the fluid contained in the circular and cylindrical fluid gaps; consequently, the squeeze mode, shear-flow mode or mixed-mode operation of the fluid could be activated separately. The performance of these fluids was found to depend on the strain direction. Additionally, the level of transmitted force was found to improve significantly under mixed-mode operation of the fluid.
“…In another study, Spaggiari and Dragoni (2014) demonstrated that the yield stress of MRF-130CG of Lord Corp. was increased by 200% as the pressure was increased to 30 bar at the highest magnetic field of 300 mT in shear mode. Becnel et al (2015) also showed that the yield stress of MRF-132DG of Lord Corp. was increased by 77% for a rotary MR energy absorber. Squeeze strengthening effects were realized when the magnetic field intensity exceeded 50 kA/m.…”
Section: Comparisons Between Theoretical and Experimental Resultsmentioning
This study focuses on experimental investigation of a fail-safe, bi-linear, liquid spring magnetorheological damper system for a three-dimensional earthquake isolation system. The device combines the controllable magnetorheological damping, fail-safe viscous damping, and liquid spring features in a single unit serving as the vertical component of a building isolation system. The bi-linear liquid spring feature provides two different stiffnesses in compression and rebound modes. The higher stiffness in the rebound mode prevents a possible overturning of the structure during rocking mode. For practical application, the device is to be stacked together along with the traditional elastomeric bearings that are currently used to absorb the horizontal ground excitations. An experimental setup is designed to reflect the real-life loading conditions. The 1/4th-scale device is exposed to combined dynamic axial loading (reflecting vertical seismic excitation) and constant shear force that are up to 245 and 28 kN, respectively. The results demonstrate that the device performs successfully under the combined axial and shear loadings and compare well with the theoretical calculations.
“…The axial activation length is only the portion of the rotor where the flux lines concatenate and is two time LP= 6 mm, while the total axial length of the rotor surrounded by the MR fluid is L=24mm. The shear stress value τ, acting on the stator wall can be directly linked to the torque measured by the sensor as follows [22,29,30] = 2 ( + ℎ) 2…”
This paper reports the experimental tests on the behaviour of a commercial MR fluid at high shear rates and the effect of the gap. Three gaps were considered at multiple magnetic fields and shear rates. From an extended set of almost two hundred experimental flow curves, a set of parameters for the apparent viscosity are retrieved by using the Ostwald de Waele model for non-Newtonian fluids. It is possible to simplify the parameter correlation by making the following considerations: the consistency of the model depends only on the magnetic field, the flow index depends on the fluid type and the gap shows an important effect only at null or very low magnetic fields. This lead to a simple and useful model, especially in the design phase of a MR based product. During the off state, with no applied field, it is possible to use a standard viscous model. During the active state, with high magnetic field, a strong non-Newtonian nature becomes prevalent over the viscous one even at very high shear rate; the magnetic field dominates the apparent viscosity change, while the gap does not play any relevant role on the system behaviour. This simple assumption allows the designer to dimension the gap only considering the non-active state, as in standard viscous systems, and taking into account only the magnetic effect in the active state, where the gap does not change the proposed fluid model.
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