Crack Initiation Behaviour in Small Root Radius Zr-2.5Nb Pressure Tube Specimens Under Monotonic and Cyclic Loading Conditions at Ambient Temperature
Bibliographic record
Abstract
To evaluate crack initiation from small radius flaws in Zr-2.5 Nb pressure tubes in operating CANDU reactors, a number of crack initiation tests under both monotonic and cyclic loading in notched tension specimens have been carried out at ambient temperature. Test specimens were machined with the tensile axis parallel to the circumferential or transverse direction in both as-fabricated and ex-service pressure tube materials. The test specimens were first pre-conditioned by subjecting them to a notch-tip creep stress relaxation cycle, and a subsequent hydride formation cycle whereby notch-tip hydrides are produced. Some specimens with no notch-tip hydride were also tested. Test specimens were instrumented with acoustic emission (AE) and DC potential drop (PD) monitoring systems for detection of crack initiation and growth. Test results indicated the following trends: (a) the existence of notch-tip hydride lowers the crack initiation stress, with the hydride effect being much stronger under monotonic loading than under cyclic loading; (b) the greater the hydrogen concentration, the lower the notch-tip hydride crack initiation stress under monotonic loading; (c) for a given alternating elastic peak stress, the smaller the root radius the greater the resistance to crack initiation; (d) as expected, the number of cycles to crack initiation is a strong function of the alternating elastic peak stress, for a given specimen geometry. An analysis of the test results and their impact on flaw evaluation methodology for Zr-2.5 Nb pressure tubes is described.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.010 | 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 teacher head, 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".