Response of piezoelectric stack actuators under combined electro-mechanical loading

The response of six piezoelectric stack actuators under electrical, mechani cal, and combined electro-mechanical loading was investigated. The focus wa s to understand the behavior of piezoelectric materials under combined elec tromechanical loading scenario, and to determine fundamental properties nec essary to model the constitutive response and optimize the actuator perform ance. Parameters that were evaluated include strain output, permittivity, m echanical stiffness, energy density, and coupling coefficients as a functio n of mechanical preload and electric field values. Results indicate that fo r certain actuators stiffness values change by more than 100% depending on the operating conditions. The magnitude of the applied compressive load sig nificantly influences strain output, electrical and mechanical energy densi ty, and coupling coefficients. Initially, the strain output and energy dens ity is enhanced with an increase in mechanical preload by as much as 60% fo r some actuators, with maximum values occurring at preloads between 25 and 40 MPa. A similar trend is observed under combined out-of-phase electro-mec hanical loading. However, linear superposition of strain outputs obtained u nder constant loading tests, does not lead to accurate predictions over the broad range of combined electro-mechanical loading conditions. This indica tes a need for more accurate constitutive relations to predict the highly n on-linear processes related to combined electro-mechanical loading. (C) 200 1 Elsevier Science Ltd. All rights reserved.