Multi-axial electrical switching of a ferroelectric: theory versus experiment

Samples of the polycrystalline ferroelectric ceramic PZT-SH were poled by a pplying an electric field at room temperature. Subsequently, an electric fi eld was applied to the samples at a range of angles to the poling direction . The measured non-linear responses in electric displacement are used to co nstruct "yield surfaces" in electric field space corresponding to the onset of ferroelectric switching. The results are compared with predictions from three models: (i) a previous self-consistent polycrystal calculation with rate-independent, non-hardening crystal plasticity; (ii) a simplified cryst al plasticity model with viscoplastic (rate-dependent) behaviour and a suff icient number of transformation systems to reproduce the polycrystalline be haviour; (iii) a phenomenological model based on rate-independent Row theor y, using kinematic hardening and a quadratic yield surface in electric fiel d and stress space. The experiments suggest that the self-consistent crysta l plasticity formulation is most able to reproduce the multi-axial electric al response and yield surface of the polycrystal. The phenomenological mode l is able to reproduce the uniaxial response accurately, but gives relative ly poor performance for multi-axial loading paths, in its present form. A t olerable compromise in multi-axial modelling is the simplified crystal plas ticity approach. This is able to reproduce multi-axial constitutive behavio ur with reasonable accuracy, whilst offering computational simplicity and s peed similar to that of the phenomenological model. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.