Magnetorheological (MR) gels are a new class of soft polymers whose properties can be controlled using a magnetic field. The functional effectiveness of these gels depends on their magnetic controllability. In this paper, an experimental investigation on the functional behavior of a particular type of magnetorheological gels under dynamic and static shear conditions in the presence of a magnetic field is studied. MR gels are prepared with micron sized polarizable carbonyl iron particles interspersed in a polymer matrix gel. The compliance of this magnetic gel can be varied under the influence of an external magnetic field. Since dynamical mechanical analysis tests are difficult to conduct in the presence of large deformations of the order of 50% and strong magnetic fields, a free decay test apparatus is designed and fabricated for obtaining the magnetic field dependent shearing response under dynamic conditions at room temperature. It is observed that a significant change in the elastic modulus occurs in the gels under a magnetic field in the range of 0.1-0.4 T. However, no significant change in the damping ratio is observed under various magnitudes of magnetic field. It is shown that the increase in shear modulus of this kind of magnetic composite gel could be as high as 59% of the zero field value for a gel prepared with 50% by weight of carbonyl iron particles.
Aluminum metal matrix composites are attractive and effective materials because of their unique properties. These properties include high specific strength, light weight, high specific stiffness, excellent wear resistance, good corrosion resistance, and greater elastic modulus compared with the base alloy. They are used in aerospace, automotive, marine, mining, and mechanical structures. Fly ash, an inexpensive waste by-product obtained after the combustion of coal in thermal power plants, is considered as a reinforcement particle in the present study. The aim is to investigate the effect of fly ash in Al-10 weight percentage (wt%) aluminum oxide (Al2O3) metal matrix composites using statistical optimization techniques. One factor and Taguchi approaches are used in planning and designing the experiments. Al/10 wt% Al2O3 with 0, 5, 10, and 15 wt% fly ash composites are prepared with the powder metallurgy technique at 300, 400, and 500 MPa compaction pressure with 90, 120, and 150-μm fly ash particle sizes. The wt% of fly ash, compaction pressure, and particle size are the process parameters. Performance parameters such as ejection force and green density, hardness, and compressive strength are considered. The ejection force and green density decreased with the increase in the weight percent of fly ash. Hardness increased with the increase in fly ash content. Compressive strength increased with the increase in fly ash up to 5 wt% and subsequently decreased.
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