Abstract
Four-point bending tests were conducted with smooth specimens of poled and non-poled lead zirconate titanate (PZT) ceramics with a tetragonal structure. The specimens poled in the longitudinal, transverse and shorttransverse directions were called PL, PT and PS specimens, respectively. The non-poled specimens were called NP specimens. The true stress-strain relation showed nonlinearity and was different between tension and compression. The nonlinearity of the stress and strain relation resulted from domain switching induced by external loading, and the degree of nonlinearity increased with easiness of domain switching under bending. The fracture strength expressed in terms of the nominal and true stresses followed the Weibull distribution. The shape parameter took a large value around 18 to 22 for PT and PS specimens, while it was the smallest around 7 to 8 for PL specimens. NP specimens took values in between. The mean strength was the largest for NP specimen and was the lowest for PL specimen. Domain switching during loading will relieve local stress concentrations of defects within the material, thus increases the strength and the shape parameter. The change in intensity ratio of the 002 to 200 diffractions can be used to assess the degree of domain switching caused by external straining.
