Mechanism of cracking in AZ91 friction stir spot welds
Bibliographic record
Abstract
The mechanism of liquid penetration induced (LPI) cracking is investigated in AZ91 friction stir spot welds. Liquid penetration induced cracking results from the following sequence of events: melted eutectic film formation in the periphery of the stir zone region, engulfment of melted eutectic films when the stir zone grows in width during the dwell period, penetration of α-Mg grain boundaries in the stir zone extremity and crack propagation when torque is applied by the rotating tool. Liquid penetration induced cracking occurs early in the dwell period during AZ91 spot welding and almost the entire stir zone is removed when the rotating tool is withdrawn. However, tool withdrawal does not provide the driving force for cracking during AZ91 spot welding; the upwards axial movement of the rotating tool at the end of the spot welding operation merely separates sections which are already cracked. The cracking tendency (the amount of the stir zone material produced during spot welding, which is removed when the rotating tool is withdrawn) is determined by the competing effects resulting from dissolution of melted eutectic films at α-Mg grain boundaries and the incorporation of eutectic rich material into the stir zone.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".