Fatigue crack growth mechanism in ferroelectric ceramics under alternating electric field: An investigation by digital image correlation technique

The deformation of crack tip in PZT ceramics under cyclic electric field loading was characterized by Digital Image Correlation (DIC) technique. Two other specimens without speckles were used to observe the physical processes during the crack propagation in-situ. The deformation of the region of interest is elucidated. Near the U-shaped notch, the DIC results directly reveal the existence of incompatible deformation. However, in the front of the newly formed crack, no incompatible deformation was observed. Additionally, in-situ observation reveals that, the crack growth occurs at the stage of crack closure when the crack propagates steadily. The observed pop-in behavior of the crack during the first cycle of electric field loading is rationalized by the interaction between the incompatible domain switching zones with and without U-shaped notch, which is consistent with the explanation of Westram et al. The subsequent crack propagation after the pop-in cannot be rationalized by the model exploited by Zhu and Yang, Wes tram et al., and Liu and Fang, which is thought to be related to three different factors - arcing, wedging and grain-to-grain interaction. The mechanism for the appearance and the disappearance of the incompatible domain switching zone near the U-shaped notch and around the tip of the newly formed crack is discussed based on the electrical boundary condition (EBC) of the crack surfaces we proposed recently.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The deformation of crack tip in PZT ceramics under cyclic electric field loading was characterized using Digital Image Correlation (DIC) technique. In-situ observation revealed the physical processes during crack propagation. The presence of incompatible deformation near the U-shaped notch was directly revealed, while no incompatible deformation was observed in the front of the newly formed crack. Crack growth occurred during the stage of crack closure. The appearance and disappearance of the incompatible domain switching zone near the U-shaped notch and around the tip of the newly formed crack were discussed based on the electrical boundary condition.