Optical metrology testing and numerical model validation of static deformations and stress concentrations of piezoelectric actuators

Piezoelectric actuators are electro-mechanical devices widely used in mechatronics robotics, vibro-acoustics, optics, active structures. Spatial and car industries are long-date users. They may be used in complex measurement systems for producing precisely controlled micro-displacements or for dynamic excitation of the structure whose response is studied. The axial compression mode multilayer actuator has several piezoelectric plates, usually of thickness 0.1 - 0.2 mm, separated by metallic electrodes. They are placed between thicker, protecting blocks placed at each end anti also in intermediate positions. The active elements are electrically connected in parallel, and mechanically in series. The assembly may be pre-stressed in a metallic housing or just resin-protected. Any mechanical stressing of the actuator with the exception of its compression may lead to its destruction. Available data about the static use of such assemblies describe their deformation as being an elongation along the axial direction, characterized by a simple translation of the end face. In fact, the hybrid, experimental-numerical study presented here shows that when applying a DC voltage, even with no mechanical load for the actuator, its strain state is complex and is accompanied by the apparition of internal stress concentrations. The actuator structural integrity may be affected and the force applied to the external mechanical load may deviate from the axial direction.