Download your Full Reports for Magnetorheological Fluid Suspension
ABSTRACT
The rheological and magnetic properties of several commercial magnetorheological (MR) fluids are presented and discussed. These fluids are compared using appropriate figures of merit based on conventional design paradigms. Some contemporary applications of MR fluids are discussed. These applications illustrate how various material properties may be balanced to provide optimal performance.
Keywords: magnetorheological fluids, MR fluids, magnetorheological fluid dampers, MR fluid
properties.
1. INTRODUCTION
Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in rheological behavior. Typically, this change is manifested by the development of a yield stress that monotonically increases with applied field. Interest in magnetorheological fluids derives from their ability to provide simple, quiet, rapid-response interfaces between electronic controls and mechanical systems. That magnetorheological fluids have the potential to radically change the way electromechanical devices are designed and operated has long been recognized.
MR fluids are considerably less well known than their electrorheological (ER) fluid analogs. Both fluids are non-colloidal suspensions of polarizable particles having a size on the order of a few microns. The initial discovery and development of MR fluids and devices can be credited to Jacob Rabinow at the US National Bureau of Standards (Rabinow, 1948a, 1948b, 1951) in the late 1940s. Interestingly, this work was almost concurrent with Winslow's ER fluid work. The late 1940s and early 1950s actually saw more patents and publications relating to MR than to ER fluids. Except for a flurry of interest after their initial discovery, there has been scant information published about MR fluids. Only recently has a resurgence in interest in MR fluids been seen (Shtarkman, 1991; Kordonsky, 1993; Weiss et al., 1993; Carlson et al.,1994; Carlson, 1994; Carlson and Weiss, 1994). While the commercial success of ER
fluids has remained elusive, MR fluids have enjoyed recent commercial success. A number of MR fluids and various MR fluid-based systems have been commercialized including an MR fluid brake for use in the exercise industry (Anon., 1995; Chase, 1996), a controllable MR fluid damper for use in truck seat suspensions (Carlson, Catanzarite and St.Clair, 1995; Lord, 1997) and an MR fluid shock absorber for oval track automobile racing.
The magnetorheological response of MR fluids results from the polarization induced in the suspended particles by application of an external field. The interaction between the resulting induced dipoles causes the particles to form columnar structures, parallel to the applied field. These chain-like structures restrict the motion of the fluid, thereby increasing the viscous characteristics of the suspension. The mechanical energy needed to yield these chain-like structures increases as the applied field increases resulting in a field dependent yield stress. In the absence of an applied field, MR fluids exhibit Newtonian-like behavior. Thus the behavior of controllable fluids is often represented as a Bingham plastic having a variable yield strength (e.g., Phillips, 1996). In this model, the flow is governed by Bingham?s equations:
where G is the complex material modulus. It has been observed in the literature that the complex
modulus is also field dependent (Weiss, Carlson and Nixon, 1994; Nakano, Yamamoto and Jolly, 1997). While the Bingham plastic model has proved useful in the design and characterization of MR fluid-
based devices, true MR fluid behavior exhibits some significant departures from this simple model. Perhaps the most significant of these departures involves the non-Newtonian behavior of MR fluids in the absence of a magnetic field (Kormann, Laun and Klett, 1994).
This paper is organized as follows. In the next section, some common MR fluid device design theory is reviewed. Simple MR fluid figures of merit based on this theory are then presented. Section 3 presents the properties of four commercially available MR fluids (Lord, 1998). Using some of these properties as a basis, figures of merit of the four MR fluids are then presented. In section 4, a few contemporary device applications of MR fluids in linear motion devices are discussed. Conclusions are presented in section 5.
Download your Full Reports for Magnetorheological Fluid Suspension
Advertisement