Nonlinear electromechanical coupling behavior of 1-3 piezoelectric composites

In this paper the orientation dependence of the electromechanical response of 1-3 piezoelectric composites with PZT5A1 fibers embedded in epoxy matrix are investigated under an AC field. The PZT fibers are initially poled along the axial direction, and when the electric field is applied to the composite at an angle θ with respect to the fiber axis, its nonlinear electromechanical response is measured as a function of θ at 0, 30, 45, 60 and finally 90°. It is found that the magnitude of the electric displacement and mechanical strain of the 1-3 system all decease with θ and the electrical response diminishes to zero at 90°. Then a two-level micromechanics model is developed to study the overall hysteresis of the electric displacement vs. the electric field, and the butterfly-shaped axial strain vs. the electric field. The first level of the model involves a thermodynamically based evolution of the product domain from the parent one in the PZT fibers, and the second one treats the PZT fibers and the inactive polymer as a two-phase composite. In each case the electromechanical interaction of the two constituent phases are fully accounted for. The two-level micromechanics model is then applied to calculate the hysteresis behavior of the PZT/epoxy composite at the tested orientations of θ, and it is observed that comparisons between our experimental data and theoretical calculations are in reasonable agreement.