Effects of stress on material properties, intrinsic and extrinsic behavior, and electromechanical response of stress -biased actuators

New actuator applications demand high displacement and load bearing capacity that can be fulfilled by stress-biased actuators, including Thunder(TM) (THin UNimorph D&barbelow;river and sE&barbelow;nsoR&barbelow;). Thunder(TM) is a composite laminate actuator based on an elastic metal layer and a piezoelectric wafer bonded together with a thermoplastic material (LaRC-SI). On cooling from the processing temperature, the difference in thermal expansion between layers creates a unique dome structure with high internal stress.;Thunder(TM) actuators were studied to provide insight into the fundamental effects of stress on the electromechanical behavior of these devices. Surface domain configurations in Thunder(TM) actuators under different stress states were investigated by x-ray diffraction and local electromechanical response along the thickness of the devices was examined using moire interferometry. Mechanical theories based on classical laminate theory (CLT) and free-edge effects were applied to model internal stress and local deformation of the devices. It was found that the piezoelectric d31 coefficient was higher for the surface region of the ferroelectric material and decreased toward the substrate. Devices with different PZT/substrate thickness ratios were studied and for the thin substrate device, the d31-coefficient ranged from ∼700 pm/V at the surface to ∼0 pm/V at the interface with the substrate, while the thick substrate device, possessing a lower stress level and gradient, ranged from ∼150 to pm/V to ∼30 pm/V.;This investigation resulted in a greater understanding of the general behavior of ferroelectric materials under the unique mechanical boundary conditions associated with these devices, and the balance between intrinsic and extrinsic contributions to the overall electromechanical response of the device.