A finite element model of ferroelastic polycrystals

A finite element model of switching in polycrystalline ferroelastic ceramic s is developed. It is assumed that a crystallite switches if the reduction in mechanically driven potential energy of the system exceeds a critical va lue per unit volume of switching material. Stress induced (i.e. ferroelasti c) switching is a change of permanent strain in characteristic crystallogra phic directions. Martensitic twinning is one example, but the strain respon se of ferroelectric materials has the same characteristics. The model is su itable for representing ferroelastic systems such as shape memory alloys an d as a preliminary model for ferroelectric/ferroelastic materials such as p erovskite piezoelectrics. In the simulations, each crystallite is represent ed by a finite element and the crystallographic principal direction for eac h crystallite is assigned randomly. Different critical values for the energ y barrier to switching are selected to simulate stress vs strain hysteresis loops of a ceramic lead lanthanum zirconate titanate (PLZT) at room temper ature. The measured stress versus strain curves of polycrystalline ceramics designated PZT-A and PZT-B are also reproduced by the model. (C) 1998 Else vier Science Ltd. All rights reserved.