A Constitutive Model for Piezoelectric Paint with Mixed Connectivity

This article presents a constitutive model for piezoelectric paint that addresses its special characteristics such as mixed connectivity and air void content. Piezoelectric paint is a composite piezoelectric material that is comprised of tiny piezoelectric particles randomly dispersed within a polymer matrix phase. The feasibility of using piezoelectric paint for ultrasonic sensing such as acoustic emission sensor has been demonstrated in the literature. With an emphasis on sensor application, a constitutive model that considers the special characteristics of piezoelectric paint such as mixed connectivity and air void content is formulated in a semi-empirical approach. The focus of this study is given to piezoelectric paints with a piezoelectric ceramic volume fraction ranging from 35% to 60%, for which some of the active particles form 1-3 connectivity, leading to higher piezoelectric activity than previous models for piezoelectric 0-3 composites predict. Percolation theory is used to empirically model the rapid increase of piezoelectric activity after a threshold level of piezoelectric ceramic particle volume fraction is exceeded in the piezoelectric paint. Such a constitutive model is very useful to sensor design since the insight gained from a parametric study of piezoelectric paint properties will provide input to optimizing paint formulation for a particular sensor design. The effect of piezoelectric particle volume fraction on the electromechanical properties of piezoelectric paint is first examined and is followed by a discussion of the air void content and polarization effects. The proposed percolation-based mixed connectivity model for piezoelectric paint sensor has been calibrated with experimental data.