Bibliographic record
Abstract
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.)
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".