Thermomechanical stress in 1-3 piezoelectric composite

The 1-3 piezoelectric composites have been developed and utilized in many application fields for several decades. For design purpose, constitutive relations have been proposed allowing the prediction of the composite properties. In fact, because the piezoelectric active phase properties are very sensitive with heat treatment or stress, these prediction laws could be inaccurate. When composites are made with a high glass-rubber transition temperature polymer phase, a high curing temperature is needed. In this case, the variation of the composite permittivity is not anymore a proportional function of the PZT volume fraction. This points out a decrease of the PZT material permittivity in the composite as a function of the PZT volume fraction instead of a constant. This is interpreted in terms of non negligible effect of the thermo-mechanical stresses induced by the polymer curing process. In-situ measurements of this stress are described. A thermomechanical model is proposed along with PZT characterization under uni-axial stress, both giving a good numerical interpretation of the composite abnormal behavior. From the relation between the PZT permittivity and polarization variation in a 1-3 composite during the curing and estimated thermal stress by the model, the thermo-mechanical stress effects on the PZT in the composite are investigated.