A theoretical study of fracture of piezoelectric solids

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Xu, Steven Xilin
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This thesis presents a theoretical study of fracture mechanics of piezoelectric materials. Based on the literature review, a selected set of basic problems related to linear fracture mechanics of plane piezoelectric media are examined. A comprehensive study of a plane piezoelectric medium with an arbitrarily oriented elliptical void and a straight crack is presented first. A set of complete analytical solutions for electroelastic fields around the void and at the crack tip are derived for different types of electric boundary conditions. It is found that solutions based on the special cases of defect orientation, i.e. defects parallel or perpendicular to the poling direction, cannot be always considered as the critical case. It is shown that the Hao and Shen type electric boundary conditions reduce to impermeable or permeable boundary conditions under practical situations. The branched cracks are then studied as the logical extension of straight cracks. It is found that branch closure happens for certain cases of branch length, branch angle and loading condition. It is shown that the asymptotic electroelastic fields at a branch tip have complex dependence on branch length, branch angle, crack orientation and the type of loading. The influence of applied electric loading is found to be more complicated and significant than mechanical loading. The issue of fracture criteria is examined next. A new stress-based criterion and two energy-based criteria are proposed to predict crack propagation in piezoelectrics. The criteria of modified hoop stress intensity factor and modified strain energy release rate suggest that, even in a symmetric case (loading and geometry), a crack may branch off from a straight path, which qualitatively agrees with available experimental findings. Finally, a general method of obtaining electroelastic singularities in piezoelectric wedges and composite piezoelectric wedges/junctions is successfully developed as a precursor to the study of fracture of multi-material systems. It is found that electric boundary conditions have a significant effect on the order of singularities for piezoelectric wedges. (Abstract shortened by UMI.)