Date: Thursday, Oct 15th
Presenter: Prof. Doru Lupascu, University of Duisburg-Essen, Essen, Germany
Piezoelectric actuators are nowadays an integral part of adaptive structures and high precision positioning devices. Their recent success in fuel injection systems is due to the rapid response to electrical signals. It permits high injection dynamics adaptable to the needs in combustion processes concerning performance and environmental safety of the exhaust gases. All actuators are embedded into some spring frame of different structure in order to warrant compressive preload on the material at all times. Fracture due the rapid dynamics which is correlated with the high inertia of the material is thus mostly avoided. Nevertheless, fatigue of ferroelectrics is observed and has many microscopic facets. Particularly when domain wall motion is involved, the effects are strong. Also unipolar electric loading alters the material response after many cycles. This is enhanced under compressive preload, because it drives the material slightly into a dynamic domain state. The material electrically stretches and changes the domain state slightly while upon electrical unloading the preload drives it back to its original shape, but not necessarily into the same microscopic state. The resultant changes in macroscopic properties are presented in this paper.