Influence of Geometric Features and Material Orientation in Piezoelectric Ceramic Materials

Orientation between loading and material property directions is a concern for both polycrystalline and single crystal piezoelectric materials. The design of devices fabricated from piezoelectric materials emphasizes alignment between principal actuation direction and a specific coupling coefficient direction. However, loading and actuation directions may not always be aligned. Complex component geometry, multiple loading types, multiple loading paths and fabrication tolerances may result in misalignment between mechanical loading direction, principal actuation direction, electrical loading direction and material property orientation. In this work a computational study is presented that examines the effects of off-axis loading as well as geometric features for piezoelectric ceramics. An ASTM dog-bone shaped tensile specimen is modified by the addition of cut-out features to provide geometry stress concentrations at various angles to the primary mechanical loading direction. Polycrystalline PZT-5A material properties are used. Mechanical loading is applied as in a standard tensile strength test. Electrical loading direction is aligned with the mechanical loading direction. The tensile specimen is also subjected to sequential mechanical and electrical loadings. In the initial condition the d₃₃ axis is aligned with the mechanical loading direction of the tensile specimen. Additional runs are made after rotating the material axes away from the principal mechanical loading axes of the tensile specimen. Stress patterns and location of maximum stress levels, indicating initial failure sites, are discussed in terms of the complex relationship between geometric features, material orientation and loading condition.