Combined Magnetic and Mechanical Sensing of Magnetorheological Elastomers

The goal of this research was to understand sensing behavior of magneto-rheological elastomers (MRE) subjected to a combined effect of magnetic fields and mechanical loadings. Experimental and theoretical studies were conducted in order to investigate the magnetoresistance and piezoresistance in MREs. In this work, MREs were made of silicon and micron sized carbonyl iron particles and cured under a magnetic field to form chain-like structures.;In the theoretical study, a finite element analysis was performed in order to understand MRE's deformation subjected to a magnetic field. The coupled magnetic field and elastic field equations were employed to determine the magnetic attraction force between the particles. An analytical approach was also proposed to predict the magnetostriction in MREs. For a simple cubic structure, the resultant change in local volume fraction of MREs was obtained based on mechanical stress and/or magnetic field induced stress analysis. In addition, magnetostriction was used in combination with magnetoresistance to determine the piezoresistivity effect of these composites under such combined conditions.;In the experimental study, the strain and electrical resistivity of structured MRE samples with a controlled constant temperature were measured simultaneously for different magnetic fields. The experimental results showed that magnetostriction in MREs with different particle volume fractions and under different compression mechanical loads can be expressed as a linear relationship using a new dimensionless number. This dimensionless number is defined for a general combined elasto-magnetic condition and can take into account all the pertinent parameters in this study. Another finding is that electrical resistivity of MREs is only dependent on the total strain changes of the material, which are caused by applying magnetic flux density and/or mechanical compression loads. The theoretical and experimental studies presented in this work will provide an alternative to the most prevalent types of mechanical sensors.