The digital image correlation technique is used for full field measurements of axial strain and transverse strain of PZT95/5 ferroelectric ceramics under uniaxial compression. Based on the variations of the axial strain and transverse strain with axial stress, the effects of poling state and poling direction of PZT95/5 ferroelectric ceramics on the domain switching and phase transformation behaviors are explored. Domain switching occurs in unpoled and Z-axis poled PZT95/5 ferroelectric ceramics separately, while domain switching in the Y-axis poled PZT95/5 ferroelectric ceramic is not observed. Domain switching strain in the Z-axis poled PZT95/5 ferroelectric ceramic has obvious influences on the developments of axial strain and transverse strain, but the influence of domain switching strain in the unpoled PZT95/5 ferroelectric ceramic is very weak, which can be attributed to the different random distribution characteristics of domain orientation. By the strain decomposition analysis, it is proved that the domain switching and the phase transition process can be decoupled, and domain switching strain and phase transformation strain can be distinguished successfully. Compared with the Z-axis poled PZT95/5 ferroelectric ceramic, the unpoled PZT95/5 ferroelectric ceramic has a small critical stress of phase transformation, while the critical stress of the Y-axis poled PZT95/5 ferroelectric ceramics is big, which may be concluded that the domain switching behavior favors the phase transformation process. The polarization released behavior of PZT95/5 ferroelectric ceramic also depends on the poling direction. The depolarization mechanism of Z-axis poled PZT95/5 ferroelectric ceramic is caused by both domain switching and phase transformation, and the Y-axis poled PZT95/5 ferroelectric ceramic is caused by only phase transformation.

Four kinds of unpoled lead zirconate titanate (PZT95/5) ferroelectric ceramics were fabricated in a range of different porosity levels by systematic additions of added pore formers. By using the non-contact digital image correlation (DIC) optical technique to measure the full-field strain, the response of unpoled PZT95/5 ferroelectric ceramics to statically applied uniaxial stresses was investigated. The influences of porosities on the mechanical behavior, domain switching, and phase transformation of the porous unpoled PZT95/5 ferroelectric ceramics were explored. All the measured stress versus strain curves for the tested porous unpoled PZT95/5 ferroelectric ceramic samples can be divided into three stages: the initial linear elastic region, the approximate plateau region, and the second linear elastic region, similar to the behavior of foam or honeycomb materials. However, the deformation mechanism of porous unpoled PZT95/5 ferroelectric ceramics should be attributed to the domain switching and phase transformation processes, but not related to the collapse of voids. With the increase of porosity, the elastic modulus, fracture strength and fracture strain of the porous unpoled PZT95/5 ferroelectric ceramics would decrease. Effect of dispersed voids does not improve plasticity of the porous unpoled PZT95/5 ferroelectric ceramics, which is mainly attributed to no effect of the pores on the obstacle and proliferation of crack propagation during the axial splitting failure processes. Critical stresses of the domain switching and phase transformation decrease linearly with increasing porosity. The macroscopic critical volumetric strain needed for phase transformation is independent of the porosity in the unpoled PZT95/5 ferroelectric ceramics.