A fully coupled three-dimensional micromechanics model based on the isofield
method is developed for the effective electrothermoelastic properties of piezoelectric
fiber-reinforced composite (PFRC) materials with poling and an electric field applied
normal to the fiber direction. In the isofield method, the strain and electric field
components parallel to the plane connecting two phases are assumed to be uniform
across both phases, and likewise for the stress and electric displacement components
normal to the connecting plane. The model employs the isofield assumptions for two
possible connectivities, which are then combined so as to yield transverse isotropy of
the effective properties when both constituents are transversely isotropic. The
assumption of uniform electric field across two phases made by some existing theories
can be achieved as a special case of the present formulation when the dielectric
constants of the fiber and matrix phases are equal. The effects of the fiber
volume fraction and dielectric ratio on the effective properties are studied for
two PFRC systems, PZT-7A/epoxy and PZT-5H/epoxy. The results are
compared with those available in the literature based on uniform electric
field assumptions. It is found that the dielectric ratio has a very significant
effect on the electromechanical and electrothermal coupling constants of
PFRCs.