Study of magnetorheological elastomers

• Main Author: Gannavarapu, Naga Leela Manohar
• Other Authors: Li Lin
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/77864
• Institution: Nanyang Technological University

Magnetorheological (MR) materials are a category of smart materials which can change their rheological properties in response to applied magnetic fields. These materials are prepared by dispersing magnetic particles in a carrier medium. Depending on the phase of the carrier medium, MR materials are classified into fluids and elastomers. MR fluids (MRF) use a liquid carrier medium and exhibit increased viscosity in the presence of a magnetic field. MR elastomers (MRE) use a solid elastomer carrier medium and exhibit an increased modulus on application of a magnetic field. A major problem with MRFs is the occurrence of sedimentation where the magnetic particles start to settle at the bottom of the fluid over time. Other problems include corrosion of the magnetic particles and thickening of the fluid over use. All these problems result in a loss of stability and deteriorated response to applied magnetic fields Due to these problems, MRFs are not durable and have to be periodically replaced. Sedimentation being the main problem, most of previous studies have mainly focussed on improving the stability and sedimentation characteristics of MR fluids. Despite improvements made to the stability of the fluids, the problems have not been fully solved. To completely mitigate this problem, recent research is looking into developing MRE brushes as an alternative to MRFs in applications where better stability or durability is needed. MRE brushes are cured in the presence of a magnetic field and form columnar structures similar to the aligned particle chains formed by fluids. In MREs, the magnetic particles are locked in the elastomer matrix and hence sedimentation does not occur even in prolonged absence of magnetic field. This study explored the fabrication of MR brushes and the dependence of the MR effect on material and process parameters namely phase of the carrier matrix, magnetic particle concentration and the curing flux density in the case of MRE brushes. The study compared the relative MR effect on fluid and solid brushes and the dependence of the MR effect on material and preparation parameters mainly concentration and curing flux density (for MREs). The results obtained indicate that MRE brushes exhibit a higher value of absolute stiffness, but a lower relative MR effect. Both MRE and MRF brushes exhibit an increase in the MR effect with increase in concentration. MRE brushes further exhibit increased MR effect with increase in the curing flux density.