The Effect of Testing Direction on DHC Growth Rate Using Zr-2.5Nb Plate
Bibliographic record
Abstract
Delayed Hydride Cracking (DHC) is a fracture mechanism responsible for several failures of zirconium alloy components.The Zr-2.5Nb alloy is used to manufacture CANDU pressure tubes, which are the primary pressure boundary in CANDU reactors.The rate of crack propagation in these tubes depends on direction.CANDU pressure tubes have anisotropic grain structure and texture due to extrusion and heat treatment.Disk-shaped hydrides preferentially form on certain crystallographic planes that are hypothesized to be responsible for the difference in DHC growth rates in certain directions.If bulk hydrides slow crack growth, then no directional difference in crack velocity will be observed when no bulk hydrides are present; i.e, where the DHC test temperature is reached by cooling to temperatures above the terminal solid solubility of precipitation (TSSP).Furthermore, below TSSP, where bulk hydrides are present, the crack velocities should begin to diverge as temperature is decreased, as oriented hydrides impede the crack growth to different extents in different directions.In this study, DHC crack velocities are determined using cantilever beam specimens with cracks propagating in both the longitudinal and through-thickness directions with and without bulk hydrides present, i.e., below and above TSSP.The DHC crack velocities in the longitudinal direction were observed to be higher than the corresponding through-thickness crack velocities with or without bulk hydrides present.Thus, the hypothesis is disproved; the orientation of bulk hydrides relative to the direction of DHC cracking does not explain the direction difference in crack velocities.Alternative hypotheses are presented.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".