3106 - SIMPLIFIED CRACK INITIATION ANALYSIS OF PIEZOELECTRIC CERAMICS UNDER CYCLIC LOADING

Crack initiation of piezoelectric ceramics under cyclic loading conditions of mechanical and electric loads was analyzed by a double cantilever beam (DCB) model. The DCB model is a simplified method to analyze a macroscopic crack by using some assumptions, and the effects of important factors on the crack can be elucidated qualitatively. The author have so far proposed that damage generated in piezoelectric ceramics by mechanical and electric loads was represented by a damage variable on the basis of the continuum damage mechanics. It has been also proposed that the damage variable was introduced into a constitutive equation of piezoelectric ceramics by using the modified cubes model and an evolution equation of the damage variable was formulated. Then, the constitutive equation and the damage evolution equation were applied to the DCB model. In the analysis by using the DCB model, a criterion of the crack initiation was based on the continuum damage mechanics; i.e. crack initiation begins when the damage variable at the crack tip attains to the critical value. In the present study, cyclic loading conditions of mechanical and electric loads were taken into account in the DCB model. By using the DCB model, the number of cycles of cyclic loading until crack initiation (or crack initiation time), fracture strain at a crack tip, and distributions of stress, strain and damage variable in front of the crack tip until the crack initiation were calculated numerically, and the effects of applied electric field on them were discussed.