Mark R. Jolly

MR fluid, foam and elastomer devices

Abstract Magnetorheological (MR) fluids, foams and elastomers comprise a class of smart materials whose rheological properties may be controlled by the application of an external magnetic field. MR fluids are liquids whose flow or shear properties are easily controlled to enable a variety of unique torque transfer or vibration control devices. MR foams, in which the controllable fluid is contained in an absorptive matrix, provide a convenient way of realizing the benefits of MR fluids in highly cost sensitive applications. MR elastomers are solid, rubber-like materials whose stiffness may be controlled to provide tunable or adjustable mounts and suspension devices.

Properties and Applications of Commercial Magnetorheological Fluids

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.

A model of the behaviour of magnetorheological materials

Magnetorheological materials are a class of smart materials whose rheological properties may be rapidly varied by application of a magnetic field. These materials typically consist of micron-sized ferrous particles dispersed in a fluid or an elastomer. A quasi-static, one-dimensional model is developed that examines the mechanical and magnetic properties of magnetorheological materials. This model attempts to account for magnetic non-linearities and saturation by establishing a mechanism by which magnetic flux density is distributed within the composite material. Experimental evidence of the viscoelastic behaviour and magnetic properties of magnetorheological fluids and elastomers suggests that the assumptions made in the model development are reasonable. It is shown that the model is semi-empirical in that it must be fit to the experimental data by adjusting a parameter that accounts for unmodelled magnetic interactions.

The Magnetoviscoelastic Response of Elastomer Composites Consisting of Ferrous Particles Embedded in a Polymer Matrix

The mechanical response of elastomer composites to applied magnetic fields is examined. These elastomer composites consist of carbonyl iron particles embedded within a molded elastomer matrix. The composite is subjected to a strong magnetic field during curing, which causes the iron particles to form columnar structures that are parallel to the applied field. This special composite geometry is known to enhance the mechanical response to the application of post-cured magnetic fields. Experimental data is presented that shows that up to a 0.6 MPa change in mechanical shear modulus (which represents 30-40% change in modulus for the materials tested) is possible in response to an applied magnetic field for a composite containing 30% (V/V) iron particles. A simple quasi-static dipole model is presented to examine the magnetoviscoelastic effect of these elastomer composites. The model is semi-empirical in that it may be fit to experimental data over a broad range of applied fields by adjusting a parameter that accounts for unmodeled multipolar magnetic interactions between particles within the composite. Such elastomer composites hold promise in enabling variable stiffness devices and adaptive structures.

Passive, Adaptive and Active Tuned Vibration Absorbers—A Survey

An overview of the recent development of tuned vibration absorbers (TVAs) for vibration and noise suppression is presented. The paper summarizes some popular theory for analysis and optimal tuning of these devices, discusses various design configurations, and presents some contemporary applications of passive TVAs. Furthermore, the paper also presents a brief discussion on the recent progress of adaptive and semi-active TVAs along with their on-line tuning strategies, and active and hybrid fail-safe TVAs.

Properties and applications of commercial magnetorheological fluids

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.

The effective magnetic properties of magnetorheological fluids

Magnetorheological (MR) fluids represent a class of smart materials whose rheological properties change in response to the application of a magnetic field. These fluids typically consist of small (@mm) magnetizable particles dispersed in a nonmagnetic carrier fluid that generally contains additives such as surfactants and antiwear agents [1]. Due to such additives, there is an outer nonmagnetic layer on the particles that keeps them from touching. The goal of this paper is to study the effective magnetic behavior of an MR composite as a function of the interparticle distance. To this end, we present and employ a model for the effective magnetic properties of MR fluids with periodic microstructure that is based on the theory of homogenization. Finally, we discuss an interpolating formula for the effective permeability of MR fluids as an extension of the work of Keller [2] and Doyle [3].

Control effort weighting in feedforward adaptive control systems

Active control of noise and vibration in large dimensional complex systems is generally accomplished with adaptive feedforward control algorithms based on the steepest descent optimization approach. This paper examines the effects of incorporating control effort weighting into the cost function that is minimized by an adaptive control algorithm. When the plant matrix is rank‐deficient, the least‐squares solution to which the control algorithm converges is nonunique. In such situations, the control signals can drift with no change in performance. Small amounts of uniform control effort weighting can enforce a unique solution at the expense of decreased performance. A nonuniform form of control effort weighting is introduced that yields a unique solution without a performance penalty. With ill‐conditioned systems, small amounts of effort weighting can provide significant reductions in the control signals with only a very small increase in residual error. A form of effort weighting is introduced for ill‐cond...

Piecewise linear model for field-responsive fluids

The Frohlich-Kennelly model provides a constitutive law for saturation that is field dependent and has been widely used for studying nonlinear properties for a variety of electric and magnetic applications. Under the Frohlich-Kennelly model, saturation begins to occupy the entire conducting domain even at low-moderate applied fields, in this paper, we first present a new nonlinear constitutive law for field-responsive fluids that depends on the local fields and allows regions where the fields have not reached a critical value to remain unsaturated. We then study numerically the nonlinear saturated model and compare the results to the Frohlich-Kennelly model and experiments performed at the Lord Corporation, Cary, NC.

Pneumatic motion control using magnetorheological technology

A new concept for pneumatic motion control is discussed that is enabled by magnetorheological (MR) technology. This concept involves placing MR braking devices functionally in parallel with pneumatic actuators. Through closed-loop feedback of a position sensor, accurate and robust motion control is achieved. Furthermore, these systems address many of the problematic issues associated with other pneumatic motion control systems such as: complexity, compliance and sensitivity to air quality. The basic system structure is presented as well as several concepts for MR-pneumatic actuators. A general control structure is proposed that can implicitly accommodate the inherent tradeoff between speed and accuracy in motion control systems. Some laboratory data is presented that explores the behavior of these systems and the nature of this tradeoff. Ideally, this technology will fill a niche between unsophisticated directional control and complex servo control systems.