Fracture and fatigue behavior of piezoelectric materials
Abstract
A model based on domain switching around a crack tip was suggested to explain fracture and fatigue behavior of PZT-4 piezoceramics. A domain switching criterion was proposed, and its validity was confirmed by the existing test data. It was found that stress and electric fields might promote or impede domain switching depending on their applied directions. An FE algorithm in conjunction with the proposed domain switching criterion was developed to analyze the stress and electric fields for CT specimens. The domain switching zones and switching induced stress intensity changes were determined, and the intrinsic toughnesses in the directions parallel and perpendicular to the poling direction were thus obtained for PZT-4. It was found that the electric field altered the switching types and switching zone size depending on its applied direction and magnitude. The variation of apparent toughness from the CT specimen under the electric fields resulted from the domain switching induced stress. Meanwhile, 2-D near tip solutions were employed to evaluate the switching induced stress intensity factor in the framework of small scale switching. The results from near tip solutions are similar to those from FE solutions. Poled and depoled compact tension specimens were performed. It was observed that the depoled material has isotropic toughness while the apparent toughness for poled materials was anisotropic in the different directions. Finite element analysis was performed for the poled CT specimen to extract intrinsic toughnesses. It was found that the intrinsic toughness is slightly anisotropic in the two directions. Domain switching was attributed to the anisotropy of apparent toughness. Compact tension tests of PZT-4 under cyclic electric and mechanical loads were conducted to successfully establish a Paris law type of fatigue crack growth model in terms of mechanical strain energy release rate. The different effects caused by the positive and negative electric fields on the fatigue crack growth were explained in terms of domain switching at the crack tip.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Mechanics|Mechanical engineering
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