Report

Fluid Structure Interactions Research Group Modelling, Characterisation and Development of New Magnetorheological Materials With Enhanced Vibration Control Performance K. Sapouna, Supervisors: Y.P. Xiong and R.A. Shenoi Faculty of Engineering and the Environment, University of Southampton, UK [email protected] Background Modelling Methodology Magnetorheological elastomers (MRE) are solid materials composed of magnetisable (usually iron) particles suspended in a low permeability carrier matrix (usually rubber). They are the solid equivalent of magnetorheological fluids that already find applications in vibration isolation systems. In the presence of an external magnetic field the particles are magnetized and form chains while trying to align in the direction of the field. As a consequence the viscoelastic behaviour of the material can be controlled. In vibration control system design, materials with dynamically variable stiffness and damping, like magnetorheological elastomers, could be useful tools. When an external field is applied to the MR elastomer during curing, the filler particles tend to align parallel to the direction of the magnetic field forming anisotropic elastomers. On the other hand, when the elastomer is cured without the presence of the field the particles are randomly dispensed inside the matrix forming an isotropic material. MR elastomers, are governed by a nonlinear stress-strain relationship with a complex modulus of elasticity that depends weekly on the frequency and strongly on the applied magnetic field. To model the material the simple Kelvin Voight viscoelastic model is used where both stiffness and damper are amplitude, frequency and magnetic field dependent. Aims Investigate the mechanical characteristics of the MR elastomers Develop a mathematical model capable of predicting the response of the material Manufacture a vibration isolator prototype device for marine applications Storage modulus ′ , , = , , Loss modulus ′′ , , = , , Damping factor tand= Figure 1: Kelvin Voight viscoelastic model ′ , , = (, ) , ′ ′ , , = =0 (, ) , =1 e=strain amplitude, ω=2 π f, B= intensity of the magnetic field − Where , = =0 Material Characterisation The mechanical properties characterization of silicon MR elastomers were performed under static and dynamic loading conditions for a range of frequencies and amplitudes following the directions of British standard BS ISO 4664-1:2005 for compression loads in rubber. ′′ ′ 2 − , = =0 and = 2 = =0 =0 Transmissibility of a SDOF system F1 M ∗ = ′(1 + ) F2 Figure 2: Modulus E of anisotropic MRE at zero field and 0.3T magnetic field Figure 6: Transmissibility curves for isotropic MRE at different strain amplitudes 2 ∗ = = 1 1 + 2 1− 2 ′ = ′ 2 + 2 Figure 7: Transmissibility curves for anisotropic and isotropic MRE at zero and 0.3T field Figure 3: Damping factor tand of anisotropic MRE at zero field and 0.3T magnetic field Conclusion Isotropic MREs have a higher MR effect than anisotropic MREs When the field is applied the natural frequency and damping factor changes Transmissibility and damping factor depends heavily on the amplitude of the applied force and thus a nonlinear model is needed Figure 4: Damping factor tand of isotropic MRE at zero field and 0.3T magnetic field Further Work Manufacture natural rubber MRE Investigate the dynamic properties of MRE under multi loading conditions Derive a constitutive equation model for both types of MRE Design and manufacture a semi active vibration isolation device and the Figure 5: Modulus E of isotropic MRE at zero field and 0.3T magnetic field This project is funded by: appropriate control system FSI Away Day 2012