Complex vibration modes in magnetorheological fluid-based sandwich beams

The study investigates the complex vibration modes of sandwich beams filled with magnetorheological fluids (MRFs). An approach is suggested involving both experiments and calculation procedures to determine the complex modes of the beams' free vibrations. Testing was done on three-layered cantilever beam filled with MRF and exposed to the magnetic field generated by an electromagnet. The purpose of the work is to analyse the influence of MRF on the beam motion and to determine the complex modes. Measurements of free vibrations of two beams filled with MRFs differing in the iron particle content by volume were taken in a purpose-built experimental set-up. Vibrations of the beam were registered under magnetic field varying in strength and for varied electromagnet's positions with respect to the beam fixed end. Thus obtained measurement data were utilised to derive the dependence of magnetic field strength and electromagnet position on beam stiffness and damping. Complex modes were obtained with the use of finite element (FE) proposed by the authors for the investigated beams. Results are given as plots of modulus and argument of the complex vibration mode against the co-ordinate defining the position along the beam axis. Results revealed major discrepancies between the values of real and imaginary parts of the beams' vibrations modes.