抄録
Four-point bending tests were conducted with smooth specimens of poled and unploed lead zirconate titanate (PZT) ceramics with the tetragonal structure. The true stress-strain relations for tensile and compressive deformations were calculated from the relations of load against tensile and compressive surface strains under the Bernoulli's assumption of beam deformation. The relations showed nonlinearity and were different respectively depending on the poling conditions. The nonlinearity of the stress and strain relation comes from domain switching induced by external loading, and the degree of nonlinearity increased with the easiness of domain switching. The fracture strength in terms of the nominal and true stresses follows the Weibull distribution. The mean strength is the largest for NP specimen and is the lowest for PL specimen. The shape parameter takes a large value around 18 to 22 for PT and PS specimens, while it is the smallest around 7 to 8 for PL specimens. NP specimens take a value in between. Domain switching during loading will relieve local stress concentrations of defects within the material, thus increase the strength and the shape parameter. The change in intensity ratio of the 002 to 200 diffractions by X-rays can be used to assess the degree of domain switching caused by external straining.
