Experimental Investigation and Modelling of Magneto Rheological Elastomer for Torsional Vibration Isolation

Abstract

Torsional vibration isolation is an effective method to mitigate unwanted disturbances arising from dynamic loading conditions. Typically this is achieved with conventional passive isolators such as centrifugal pendulum absorbers, torsion springs, sprocket dampers, fluid cased vibration dampers and others. A drawback of the existing passive isolators is the inability to tune themselves to varying operating conditions. With smart materials as suitable substitutes, the conventional passive systems have attained attributes of semi-active and active control isolators. Of the various available smart materials, the Magnetorheological Elastomers (MRE) offers a field-dependent property variation for variable operating parameters. Though the MRE has been effectively studied to isolate the structures in the linear/translatory systems, its capabilities as an effective torsiocal isolator are yet to be understood fully. In lieu of the same, in the present study, Magnetorheological Elastomers' attributes as an effective torsional vibration isolator have been explored. To comprehend the isolation capabilities of Magnetorheological Elastomers, a thorough understanding of the influencing parameters is necessary. Hence, the initial part of the current study focuses on the dynamic property characterization of the Magnetorheological Elastomers under torsional loading conditions. The dynamic properties of Magnetorheological Elastomers are predominantly affected by variation in the input displacements, applied magnetic fields and input frequency. Though the characteristics have been extensively studied under lateral shear, the property variations under torsional shear have not been explored. The present study develops a novel method to study the influence of angular displacement, applied magnetic fields and input frequency on the dynamic properties of Magnetorheological Elastomers under torsional loading conditions. The experimental setup is developed according to the ISO 10846-2 standard to evaluate the dynamic torsional stiffness and loss factor variations. Viscoelastic properties represented in-terms of complex torsional stiffness and loss factor are estimated from the Lissajous curves within the linear viscoelastic (LVE) limit. Experiments are conducted for varying input angular displacements (in the Linear Viscoelastic limit) and input frequency (in the range of 10Hz to 30Hz). The frequency range corresponds to the torsional frequency range of shafts rotating in the lower speed vii range under 2000 rpm. Magnetic field sensitive characteristics are evaluated under the field produced by a custom-made electromagnet in the range of 0T to 0.3T. The volume fraction of the CIP is set at 27% for the RTV based isotropic MRE. The results reveal a strong influence of field-dependent variations on the complex stiffness compared to the input frequency. Variations observed in the loss factor suggest a dominance of the imaginary part of the complex stiffness on the energy dissipation. The reduced field-induced enhancements in the complex stiffness are interpreted from the Magneto-static and structural based numerical simulations using ANSYS 19.1. The angular displacement dependent variations highlight the effectiveness of the developed method in capturing the rheological properties under torsion. Changes in the dynamic torsional stiffness suggest the dominant behaviour of the input angular displacement. The bound rubber theory is used to interpret the displacement-dependent variations on the torsional stiffness. It is also observed that the MRE's damping capacity depends on the angular displacement and the dissipation capacity of the elastomer is evaluated in terms of loss factor. Results indicate a significant contribution of the interfacial damping over the intrinsic and magneto-mechanical hysteresis damping. To formulate the actual implementation of the MRE as a semi-active isolator, it is required to model the complex behaviour of the MRE through its stiffness and damping. Though much research has been carried out in understanding MR fluids' behavior, the same cammt be said of its elastomer counterparts. The constitutive relationship between the operating parameters is derived using a viscoelastic parametric modelling technique based on the Kelvin-Voight model. Results highlight the derived model's effectiveness in predicting the experimentally obtained viscoelastic behaviour of the Magnetorheological Elastomers regarding the stiffness and the energy dissipation capacity. To evaluate the Magnetorheological Elastomer isolator's isolation capabilities, a novel, custom-made SDoF torsional isolation system is developed. Field-dependent reduction in the transmissibility ratio highlights the semi-active vibration capabilities of the isolator and a maximum reduction of 42% is observed in the transmitted amplitudes. Further, a shift in the natural frequency is detected due to the field-induced viii variations in the isolator's torsional stiffness. The isolation capabilities are calculated for different input angular displacements, inertia and magnetic fields and the effect of the individual parameters is studied. The torsional stiffness and the damping factor are ascertained individually for the individual parameters. Also, a model-based PID control strategy is adopted to assess the semi-active vibration capabilities of the Magnetorheological Elastomer isolator.