Experiment Characterization
Optimal Carbonyl Iron Powder Content Level
It was shown in literature \cite{bastola2020review} that the saturation magnetization improves by increasing the content of the Carbonyl Iron Powder (CIP). Creating MRE with high CIP content is beneficial to the valve design as it decreases the electric current required to regulate the airflow. However, higher CIP content in MRE results in significantly reduced flexibility and difficulties in polymerization. The bonding between the MRE membrane and the silicone base of the valve can also be an issue. To investigate the optimal CIP content level for fabricating the MRE valves, a set of samples as shown in Figure \ref{397777}(A) were tested. These samples were made by bonding an MRE membrane (2mm thickness) to a silicone membrane (2mm thickness) while leaving an air channel in their middle. The detailed schematics used for the experiments are shown in Figure \ref{397777}(B). The pressure within the air channel of the samples was gradually increased until the sample fails and the pressure was monitored during the whole process. The pressure at failure was then recorded. For each CIP content level, three identical samples were made and tested. The mean and standard deviation of the pressure at failure for different CIP levels are presented in Figure \ref{397777}(C). Two different failure modes were observed. For samples with a CIP level of no more than 80 wt% , the MRE membrane undergoes a burst in its center under high pressure and leaves a crack. The pressure at failure here is consistently higher than 150 kPa. For CIP levels higher than 80 wt% , the MRE layer delaminates from the silicone layer, indicating that the bonding between the two layers is the dominant weakness. The pressure at failure here drops significantly below 50 kPa. The standard deviation also increases, indicating a lack of consistency for samples with too high CIP levels. This inconsistency is most likely brought in during the fabrication process, as the higher CIP level significantly increases the viscosity of the uncured MRE and therefore makes it difficult to be cast into an even-thickness MRE membrane. Based on the results presented in Figure \ref{397777}(C), the CIP content level chosen for fabricating the MRE valves is 80 wt%, as it is the highest CIP level achieved without sacrificing too much strength.