Doctor of Philosophy
Department of Mechanical, Materials and Mechatronic Engineering
Guo, Miao, Development of adaptive structures working with magnetorheological elastomers and magnetic force, Doctor of Philosophy thesis, Department of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2013. http://ro.uow.edu.au/theses/3859
The work presented in this thesis consists of two major parts: (a) An investigation of the dynamic response of magnetorheological elastomers (MREs) sandwich beam under non-homogeneous magnetic field strength; (b) The development of a positive-negative-stiffness vibration isolator based on MREs and magnetic force.
(I) The sandwich structure theory is based on the Mead & Markus model and was extended such that a vibration differential equation of an MRE sandwich beam was deduced. The coverage area and strength of the external magnetic field on the dynamic characteristics of a sandwich structure was also studied. It focused on an investigation of MRE cantilever sandwich beam and a clamped-clamped sandwich beam.
MREs based on silicone rubber and carbonyl iron particles were fabricated and their dynamic performance under magnetic fields of different strengths were tested using a rheometer.
An MRE sandwich beam was fabricated by placing an MRE between two thin layers of aluminium. An experimental test rig was set up to investigate the vibration of the MRE sandwich beam under non-homogeneous magnetic fields. Both experimental results showed that the first natural frequency of the MRE sandwich beam decreased as the magnetic field that applied on to the beam was moved from the clamped end of the beam to the free end of the beam. The MRE sandwich beam also had the capability of shifting the first natural frequency left when the magnetic field in the activated regions was increased.
(II) A novel positive-negative-stiffness vibration isolator was developed using MRE and a magnetic force to vary the stiffness. This vibration isolator can work over a relatively wide range of excited frequencies. A mathematical model of the isolator was derived and a prototype of the positive-negative stiffness was fabricated. The test rig was setup and the transmissibility of the system under different current intensities was tested. The dynamic characteristics of the isolator under different current intensities were simulated with Matlab. Both the experimental and simulated results show that the system’s natural frequency increased when a positive current was applied and decreased when a negative current was applied. The simulation results also demonstrated that the positive-negative isolator can efficiently suppress vibration after the current in the coils has been tuned.