Xianzhou Zhang

Development of an MR-brake-based haptic device

This paper describes the design, testing and modelling of a magneto-rheological (MR) fluid brake as well as its application in a haptic device. The MR device, in disc shape, is composed of a rotary shaft and plate, an electromagnetic coil, MR fluids, and casings. The working principle of the actuator is discussed and the transmitted torque equation employed by using the Bingham plastic model. The optimal dimensions of the actuator were obtained by finite-element analysis using the COSMOSEMS package. Following manufacturing and fabrication of the actuator prototype, the steady-state performance of the MR actuator was measured using a force gauge. The experimental results show that the actuator exhibits hysteresis behaviour. A sub-hysteresis model was then proposed and the model parameters were identified. Example applications of this actuator in virtual reality are demonstrated.

The rheology of shear thickening fluid (STF) and the dynamic performance of an STF-filled damper

This paper presents a study of the rheological properties of shear thickening fluid (STF) and its application as a damper. The STF samples, with different weight fractions, were prepared by dispersing nanosized silica particles in a solvent. By using a parallel-plate rheometer, both steady-state and dynamic experiments were carried out to investigate the rheological properties of STFs. Experimental results indicated that these suspensions show an abrupt increase in complex viscosity beyond a critical dynamic shear rate, as well as this increase being reversible. Working with the fabricated STF materials, a prototype damper was fabricated and its dynamic performances were experimentally evaluated. An equivalent linear model through effective elastic stiffness and viscous damping was developed to address both the damping and the stiffness capabilities of the damper. Also, a mathematical model was developed to investigate working mechanisms of STF-based devices.

Study on the mechanism of the squeeze-strengthen effect in magnetorheological fluids

Current magnetorheological (MR) fluids have the limitation that their yield stresses are not strong enough to meet some industrial requirements. X. Tang, X. Zhang, and R. Tao [J. App. Phys 87, 2634 (2000)] proposed a method to achieve high-efficiency MR fluids by study of squeeze-strengthen effect. But there is little report on its mechanism. This paper aims to investigate this effect through experimental and theoretical approaches. For this purpose, an apparatus is designed to experimentally study the mechanism of this squeeze-strengthen effect. Taking account of a modified magnetic dipole model and the friction effect, a semiempirical model is proposed to explain this effect. In addition, this model is expected to study the squeeze-strengthen effect in electrorheological fluids.

Study on magnetorheological shear thickening fluid

In this paper, a magnetic-field-controlled and speed-activated magnetorheological shear thickening fluid (MRSTF) is presented. We fabricated a kind of shear thickening fluid (STF) which was composed of nanosize silica particles suspended in a solvent, ethylene glycol, at high concentrations. Then the micron-size carbonyl iron particles with different volume fractions were added to the STF to fabricate the MRSTF. Their dynamic properties in different shear strain rates and magnetic fields were tested by using a rheometer. The suspension shows an abrupt increase in complex viscosity beyond a critical dynamic shear rate and a magnetic-field-controllable characteristic, as well as being reversible.

Analysis and fabrication of patterned magnetorheological elastomers

This paper presents analysis, fabrication and characterization of patterned magnetorheological (MR) elastomers. By taking into account the local magnetic field in MREs and particle interaction magnetic energy, the magnetic-field-dependent mechanical properties of MREs with lattice and BCC structures were theoretically analyzed and numerically simulated. Soft magnetic particles were assembled in a polydimethylsiloxane (PDMS) matrix to fabricate new MR elastomers with uniform lattice and BCC structures, which were observed by a microscope. The field-dependent moduli of the new MR elastomers were characterized by using a parallel-plate MR rheometer. The experimental results agreed well with numerical simulations.

A study of the magnetorheological effect of bimodal particle based magnetorheological elastomers

This paper presents theoretical and experimental studies of the mechanical performance and magnetorheological effects of magnetorheological elastomers (MREs) fabricated with mixtures of large and small particles. First of all, an effective permeability model was developed to theoretically analyze the MR effect of bimodal particle based MR elastomers. From the theoretical analysis, an optimum volume fraction was derived which resulted in enhanced MR effects. Two categories of iron products with different particle sizes of 50 and 5? ?m were used to fabricate a series of bimodal MRE samples. Their mechanical performances were characterized by using an MR rheometer. Experimental results agreed fairly well with theoretical analysis. The theoretical prediction of the optimum mixture ratio between large and small size particles was experimentally verified.

Thixotropy of MR shear-thickening fluids

Particle sedimentation is a key issue of conventional magnetorheological (MR) fluids. We recently fabricated MR shear-thickening fluids (MRSTF), which can work as novel MR fluids without particle settling. This merit of the material against particle settling is attributed to the thixotropy property. By using shear-thickening fluids as a base medium, a series of MRSTF samples was prepared and their rheological properties were tested. It was found that when the weight fraction of the STF base is above a threshold value of 15%, the MRSTF exhibits a significant thixotropy phenomenon, which greatly reduces the settling problem of MR fluids and consequently increases the stability of MR fluids. A theoretical approach was proposed to verify the experimental studies.

Development of a force sensor working with MR elastomers

This paper presents the development of a new force sensor with MR elastomer as a sensing element. One key element in this study was to find a suitable material with high sensing capabilities which can be used for developing a sensor. Thus different MR elastomers, with ingredients of carbonyl iron particle, graphite, silicone oil and silicone rubber, were manufactured and measured with a modified rheometer. The effects of additives on the sensing capabilities were systematically investigated and an optimal MR elastomer sample was selected for design and manufacturing of a force sensor prototype. The development sensor prototype consists of three units: mechanical unit, electrical circuit and LED display unit. The mechanical unit includes the MRE sample and the interface to the electronic circuit. A signal conditioning circuit was developed for calibrating output voltages, which are displayed on a LCD panel. The components of the electronic part were soldered on a board and communicate with the mechanical part for signal detection and testing. Overall the developed new MR elastometer based force sensor is able to detect external forces at the selected force ranges.

Magnetorheological Elastomers and Their Applications

Magnetorheological elastomers (MRE) are smart materials whose modulus or mechanical performances can be controlled by an external magnetic field. In this chapter, the current research on the MRE materials fabrication, performance characterisation, modelling and applications is reviewed and discussed. Either anistropic or isotropic or MRE materials are fabricated by different curing conditions where magnetic field is applied or not. Anistropic MREs exhibit higher MR effects than isotropic MREs. Both steady-state and dynamic performances were studied through both experimental and theoretical approaches. The modelling approaches were developed to predict mechanical performances of MREs with both simple and complex structures. The sensing capabilities of MREs under different loading conditions were also investigated. The review also includes recent representative MRE applications such as adaptive tuned vibration absorbers and novel force sensors.

Development and analysis of a variable stiffness damper using an MR bladder

This paper presents the development of a magnetorheological (MR) fluid-based variable stiffness damper and analysis of its applications in vibration suppression. The MR fluid isolator used a MR valve control unit and bladders to achieve a continuously variable stiffness and damping of relatively large scope. A mathematical model of the isolator was derived, a prototype of the MR fluid isolator was fabricated, and its dynamic behaviour was measured in vibration under various applied magnetic fields. The effective stiffness and damping coefficients of the isolator under various magnetic fields were identified and the dynamic performance of the isolator was evaluated by simulation. The simulation results demonstrated that the MR bladder system developed can efficiently suppress structural vibrations.