Influence of the Load Dependent Material Properties on the Performance of Multilayer Piezoelectric Actuators

Abstract

Multilayer piezoelectric actuators are commonly used to control injection valves in modern combustion-engines. Their structural and functional integrity is associated with the loading conditions as well as with the actuator-design. In service mechanical stresses are an inherent loading scenario of such electro-mechanical converter components. Internal inhomogeneous mechanical and electrical fields may harm their integrity and accelerate phenomena such as degradation, fatigue and subcritical crack growth. A way to delay these phenomena is to reduce the tensile field-amplitudes by operating these piezoelectric components under a low compressive bias-stress. However, this also may influence the component’s performance. Interestingly, this bias-stress enhances its strain characteristics. In this work the electro-mechanical behaviour of a multilayer actuator has been characterised under different loading conditions using an adapted universal materials testing machine (UTM). The stiffness of the UTM has also been adjusted to simulate realistic conditions. This adaption enables the measurement of mechanical properties– such as mechanical stress and the corresponding strain– and electrical quantities, i.e. the electrical charge (or electric displacement) and the applied voltage (or electrical field) to the actuator. As a result, the stiffness, hysteresis-loops, such as the dielectric and butterfly curves and the stress-strain loop, as well as the actuator’s performance, can be measured.