Response of Electrorheological Fluid-Filled Laminate Composites to Forced Vibration

Laminate composite beams consisting of metal or polystyrene outer strips and an electrorheological (ER) fluid (corn starch in corn oil) filler were constructed and tested using the standard Oberst test for viscoelastic materials. Application of an electric field of 2 kV/mm increased both the frequency of the various resonance modes and the loss factor associated with each. The apparent elastic modulus and loss factor of the composite beam and those of the ER fluid alone were calculated employing standard ASTM equa tions. Both modulus and loss factors of the composite beams decreased with resonance mode or frequency. The calculated shear modulus of the ER fluid increased with fre quency and the loss factor decreased, their magnitudes being in reasonable accord with those measured directly on the fluid employing a rheometer. However, the calculated mag nitude of the increase (GPa) of the apparent modulus of the metal/ER fluid composite beams with electric field and the fact that it decreases with frequency suggest that the standard ASTM equations do not adequately describe the vibration characteristics of the ER fluid laminate composites. A relatively simple on-off control system is illustrated as a potential application of ER fluid composites for vibration control in structural materials.