Characterisation and Modelling for Elastomeric and Gel-Like Magnetorheological Materials

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Magnetorheological (MR) material is an aspiring branch of smart material. It can change its mechanical properties rapidly and reversibly subjected to an externally applied magnetic field, so-called MR effect. Due to the sensitivity to magnetic field and the versatility in physical states, i.e., liquid (MR fluid), gel-like (MR gel), elastomeric (MR elastomer), MR materials have tremendous application potential in engineering industries, especially in civil engineering, involving vibration reduction and isolation for infrastructures. However, some MR materials have inherent limitations: sedimentation and instability of MR fluid, and low MR effect and large energy consumption of MR elastomer. MR gels were fabricated to gain the merits of both MR fluid and MR elastomer, i.e., high MR effect and excellent sedimentation resistance. This work focuses on the two types of MR materials: MR elastomer and MR gel. They both significantly improve the sedimentation problem of MR fluid, yet the current knowledge and design techniques are inadequate to deliver efficient and effective applications. For MR elastomer, this work implements the hybrid magnets (permanent magnet and electromagnet) configuration in both characterisation and engineering applications to resolve the large energy consumption issue. Moreover, an improved magnetic circuit model is proposed to serve as an effective and efficient approach for designing and analysing MR elastomer devices with complicated structures, i.e., hybrid magnets and laminated structure. In a pioneering manner, the field-dependent dynamic stress-strain hysteresis of MR gel is characterised and shows a unique stress overshoot phenomenon. A simple hysteresis model with support vector machine generalisation technique is formulated and validated the experimental results. Finally, thixotropy of MR gel is characterised by a proposed test protocol considering the variables of shear rate, magnetic field, shearing time and resting time. A thixotropy model for MR gel is proposed and agrees well with the experimental date under all test conditions considered.
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