A COMPARATIVE-STUDY OF AC AND DC ELECTRORHEOLOGICAL MATERIAL BASED ADAPTIVE STRUCTURES IN SMALL AMPLITUDE VIBRATION

The present investigation focused on the controllability and reliabili ty of AC and DC electrorheological (ER) materials based adaptive beams . The mechanical and rheological reliability of such adaptive structur es was studied over an extended time period. Modal vibration frequenci es exhibited relatively stable behavior over time, while modal loss fa ctors were observed to vary significantly. Significant structural stif fening in response to electric held was observed with the DC ER materi al, while damping dominated the changes observed with the AC ER materi al. Oscillatory shear experiments with the two materials provided insi ght into the cause of the observed differences between AC and DC mater ial based structural response. At small strains both ER materials beha ved in a nonlinear viscoelastic fashion. The relative contributions of nonlinear loss and storage moduli were found to cause the observed di fferences in the performance of these adaptive structures. The structu ral time response upon the application or removal of electric field wa s also studied. Both AC and DC structures responded rapidly to the app lication of electric field. For the case of electric held removal, how ever, it was found that the held strength and application time, ER mat erial type. and structural excitation amplitude ail influenced respons e time.