An accurate technique for pre-yield characterization of MR fluids

Abstract

This study is concerned with the characterization of two types of magnetorheological (MR) fluids (MR 122EG and MR 132DG) in the pre-yield region. A phenomenological model is proposed for characterizing the complex shear modulus of the MR fluids as a function of both the magnetic flux density and the excitation frequency using the experimental data acquired for both the fluids. The experiments were conducted with a sandwich beam structure with an aluminum face layer and MR fluid as the core layer. A nearly uniform magnetic field was applied across the sandwich beam using two ceramic permanent magnet bars. The frequency response characteristics of the sandwich cantilevered beam were subsequently measured under harmonic excitations swept in the 0 to 500 Hz frequency range considering different densities of the applied magnetic flux, ranging from 0 to 90 mT. Dynamic responses of the structure were also obtained through analysis of a finite element (FE) model developed using the classical plate theory. The frequency and field-dependent complex shear moduli of the two MR fluids were identified from both the experimental data and the FE model results. The validity of the proposed methodology is demonstrated by comparing the FE model results with the experimental data for a copper sandwich structure comprising the two MR fluids.