Influence of Hydrides upon the Fatigue Initiation Behavior of Irradiated Zircaloy-2
Bibliographic record
Abstract
In a reactor, the properties of zirconium alloy components change significantly from their start-of-life condition. The accumulation of irradiation damage increases the strength of these alloys, while the aqueous corrosion results in hydrogen pickup. The combination of increased strength and elevated hydrogen content enhances the susceptibility to hydride related failures such as delayed hydride cracking. The motivation behind this work was to investigate whether the fatigue crack initiation behavior may also be affected by the presence of aligned notch-root hydrides in irradiated material. In collaboration with Canadian Nuclear Laboratories, Rolls-Royce has undertaken a program of testing to investigate this effect using notched specimens of irradiated and hydrided Zircaloy-2. Variables that were investigated included temperature, hydrogen content, notch geometry, and hydride alignment. Hydride alignment was achieved by applying preconditioning thermomechanical cycles to the specimens prior to commencement of isothermal fatigue cycling. Batches of specimens subjected to different numbers of preconditioning thermomechanical cycles were produced as a means to vary the density of hydrides around the root of the notch. Isothermal fatigue loading cycles were then applied to specimens that had different amounts of hydride alignment to quantify the sensitivity of fatigue initiation behavior to the presence of hydrides at the notch root. The results indicate that notched irradiated Zircaloy-2 exhibits a fatigue limit that is sensitive to temperature and test frequency. At load ranges above the fatigue limit, the presence of notch root hydrides reduces the number of cycles to crack initiation and also reduces the number of cycles to achieve a given crack size. Greater hydride alignment at the notch roots does not influence the fatigue limit; however, it may further reduce the rate of crack extension. The presence of hydrides under sharper notches may influence the fatigue limit, while a reduction is not observed under blunter notches.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".