Effects of foam shape and porosity aspect ratio on the electromechanical properties of 3-3 piezoelectric foams

Three-dimensional finite element models are developed to completely characterize the role of microstructural features such as foam shape and porosity shape in determining the elastic, piezoelectric and dielectric properties of 3-3 type piezoelectric foam structures. Upon identifying 35 characteristic foam structures that capture a wide range of microstructures, the influence of foam shape, porosity aspect ratio and volume fraction on the effective properties of foam structures is examined. The material properties of the foam structures and their corresponding figures of merit are shown to be strongly dependent on the microstructural features. For foam structures with a particular shape, the principal electromechanical properties in the longitudinal direction (i.e. along the poling direction), such as C22, κ22 and e22, are lower for the piezoelectric foam structures with flat porosity with lower aspect ratios as compared to other foam structures with elongated porosity with higher aspect ratios. The piezoelectric figures of merit such as the piezoelectric charge coefficient (dh), the piezoelectric voltage coefficient (gh) and the hydrostatic figure of merit (dhgh) of the foam structures can be enhanced significantly by modifying the shape of the porosity. For example, in the equiaxed foam structure of PZT-7A with 30% porosity, dh, gh and dhgh are, respectively, increased by 175, 1000 and 1800%, by changing the shape of the porosity from a cuboidal shape (with aspect ratio of 1) to a flat-cuboidal shape (with an aspect ratio of 0.25).