Mechanical Characterization of PZT Ceramics for Multilayer Piezoelectric Actuators

Multilayer piezoelectric actuators (MPA) are commonly used to control injection valves in modern combustion engines operating in a temperature range from -40 degrees C up to 125 degrees C. They consist of a stack of very thin piezoceramic layers, mostly based on Lead Zirconate Titanate (PZT) material with interdigitated metallic electrodes in between. In this work the mechanical properties of both pure piezoceramic material and the multilayer structure are investigated in terms of strength and crack growth resistance. The results of strength tests are interpreted in the mainframe of Weibull theory, and fractographic analyses are performed in order to get information about the weakest links in the microstructure. The crack growth resistance is determined using the single-edge V-notched beam (SEVNB) method in both materials to estimate the influence of the electrodes on crack propagation. The influence of the texture (i.e. domain-orientation) is assessed with indentation techniques under combined mechanical and thermal loads. In addition, with the aid of Raman spectroscopy it is shown that crack growth anisotropy is intimately linked with domain switching segregation; cracks arrest earlier when propagating along a direction where domain switching is highly favored. Based on experimental results, guidelines for an improved design of MPA are also given.