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MR Fluid Assembly and Testing

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A typical MR fluid used by Rabinow was made of 9 parts by weight of carbonyl iron to one part of silicone oil. Because of the large range of forces necessary a number of different MR fluids are employed: Carbonyl iron powder with two different particle size ranges (2-5micron and 4-7micron) mixed with silicone oils with five different viscosities (h=0.00935, 0.01906, 0.34055, 0.974, and 12.1875 Pa.s) are used to make different samples of MR fluids. In these samples different weight ratio of iron powder to silicone oil was used. A few of the MR fluid samples are presented in Table 1. These MR fluid samples are tested in a MTS machine commonly used for tensile tests.
 
SampleCarbonyl iron powderOil (carrier fluid)weight ratio of iron powder to oil

shear stress

(kPa)

weight (gr)Particle size (m)weight (gr)Viscosity (cSt)Viscosity (Pa-s)
176.52-522.25300.0273.427
280.02-59.183500.340559 (Rabinow's)-
380.02-511.443500.340557-
480.02-516.163500.34055535
580.04-720.023500.34055438
680.02-515.8410000.974540

Table 1: Hand made MRF ingredients

(a) MTS machine

(b) Linear sponge damper

Figure 1: Linear sponge damper used for testing the MR fluid samples. The linear sponge based damper uses a polyurethane sponge saturated with MR fluid to eliminate the sealing problem. A copper coil of gauge 28 with 400 coil turns, creating 10 ohms of resistance, is used that can carry a maximum current of 2 amps. The resulting force-velocity graphs of the damper for varieties of MR fluids are used to determine the most practical MR fluid with the greatest range (in terms of force) in on-state and low viscosity in off-state. The MTS machine results of this MRF sample is presented in Figure 2.

 

 


Figure 2: MTS test results for MRF sample