Recent Progress in Development of Ductile Fracture Arrest Methodology Based on CTOA: Test Standard, Transferability and Methodology
Bibliographic record
Abstract
Abstract Significant progress has been made in development of a new fracture arrest methodology based on a toughness parameter designed to characterize propagation — the crack-tip opening angle (CTOA). A CTOA test procedure using lab-scale DWTT-type specimens has been standardized by ASTM, and recently published experimental work has demonstrated transferability of CTOA from DWTT to full-scale pipe. This paper will present the basic methodology for determination of CTOA using DWTT-type specimens (i.e., ASTM E3039) and other specimens such as modified double-cantilever-beam (MDCB). Recent numerical studies using cohesive zone models (CZM) and others based on damage mechanics will be discussed, including models of full-scale pipe fracture. The effects on CTOA of loading rate, specimen flattening and constraint (bending vs. tension) will be reviewed. The effect on CTOA of loading rate between quasi-static and impact (covering five orders of magnitude) is small or negligible, being within experimental scatter. Observed differences between surface and mid-thickness CTOA values will be discussed. Models of DWTT specimens using damage mechanics have shown that the CTOA for tensile loading is the same at the surface and mid-thickness and equal to the mid-thickness value for bend loading, but that the surface CTOA is significantly larger than the mid-thickness CTOA in bending. Model calculations have revealed the dependence of crack velocity on stress for a given CTOA, enabling construction of fracture resistance curves (pressure required to propagate fracture as a function of crack velocity). These first-principles curves based on CTOA can then be used in the Battelle two-curve model (BTCM) to replace empirical resistance curves based on Charpy absorbed energy (Cv). It has been known for some time that Cv over-represents the propagation resistance for high-strength high-toughness steels, requiring empirical “correction factors” to Cv in the BTCM. Experiments have shown that there is a non-linear correlation between Cv and CTOA, explaining the need for correction factors to Cv and supporting the use of CTOA as a more appropriate propagation toughness.
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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 | 0.012 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.004 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.002 | 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".