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

Abstract

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.

Characterization of commercial magnetorheological fluids at high shear rate: influence of the gap

“…The producer datasheet reports a yield stress around 50 kPa when the magnetic field is above 300 KA/m. Although it is not specified in the producer TDS we can find some information in literature work [8][9][10][11][12][13][14][15][16][17] about the average dimension of the spherical MR particles, which is around 20µm, with a density around 2950-3150 kg/m 3 . The settling and the agglomeration of the particles is prevented thanks to proprietary surfactants and additives.…”

“…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…”

Smart materials: Properties, design and mechatronic applications

“…One chance is to increase the volume fraction 48 of the ferromagnetic particles to increase the magnetic saturation; another interesting possibility is to exploit the static pressure of the fluid to obtain larger yield stresses 49,50 as shown with some controversial results in several literature works. [51][52][53][54][55][56][57][58] In order to exploit MRFs' properties, there are three main ways envisioned in current engineering applications: flow mode, shown in Figure 2 Flow mode architectures: Design principles of MR-based damping devices. The flow mode exploits the fluid between two fixed walls, while the magnetic field is normal to the flow directions and is typical for linear damper applications (Figure 2(a)).…”

Experimental validation of a novel magnetorheological damper with an internal pressure control

“…Hence, as the damper is compressed there is no gas force to push against, making the damping more sensitive. Further studies on the behaviour of MRFs have proved that direct-shear mode and flow mode when coupled with a unidirectional compression can provide higher yield stress (Guo et al 2013, Tang et al 2000, Tian et al 2002a,b, 2010, Zhang et al 2004, Spaggiari and Dragoni 2012, 2013, Becnel and Wereley 2013, Becnel et al 2015, Mazlan et al 2008. The phenomenon is known as squeeze strengthening effect.…”

“…Further studies on the behaviour of MRFs have proved that the direct shear mode and the flow mode when coupled with a unidirectional compression can provide higher yield stress (Becnel and Wereley, 2013; Becnel et al, 2015; Guo et al, 2013; Mazlan et al, 2008; Spaggiari and Dragoni, 2012, 2013; Tang et al, 2000; Tian et al, 2002a,b, 2010; Zhang et al,2004). The phenomenon is known as the squeeze strengthening effect.…”