Investigation of orientation effects on the electro-mechanical coupling behavior of 1-3 piezoelectric composites under compression

The electro-mechanical responses of 1-3 piezoelectric composites with PZT5A1 fibers embedded in an epoxy matrix are investigated under compressive loading. When the applied loading direction is not parallel to the polarization and fiber directions of the PZT fibers, the corresponding electrical and mechanical responses can be dramatically affected. Here both experimental testing and theoretical modeling are carried out to study such orientation effects on 1-3 piezoelectric composites. The testing results indicate that, as the loading direction changes from 0°, to 30°, 45°, 60° and finally 90° to the initial poling direction (which is also the PZT fiber direction), the magnitude of the electric displacement and mechanical strain of the system all decrease and the electrical response will diminish to zero at 90°. On the other hand, a two-level micromechanics theory based on irreversible thermodynamics and the physics of domain switching is applied to predict such orientation dependency of the electro-mechanical coupling behavior of the composite system. The first level is based on PZT fibers only which consist of parent and switched domains due to external loading, and the second level is based on a larger scale consisting of PZT fibers and an electrically inactive polymer matrix. The theoretical results are found to be in reasonable agreement with our experimental data.