Development of a Material Selection Procedure for Natural Gas Pipelines based on the Crack Tip Opening Angle
Bibliographic record
Abstract
In this thesis, extensive finite element simulations of ductile fracture propagation were analyzed using the cohesive zone model (CZM) and the constant CTOA model. The CZM was used to examine the effect of loading mode on the CTOA through comparing the results of a DWTT model to that of a pipe model. A novel constant CTOA model was proposed in which it was integrated into the explicit time integration solver for dynamic simulations. The proposed model was compared with previous published numerical data to serve as verification and then compared to recent experimental data for validation. The proposed model reduced the runtime from previous implementations by 94% while maintaining less than 2% difference. The analysis of the experimental data was the first use of the constant CTOA model to reproduce experimental fracture velocity data. Smoothed particle hydrodynamics was implemented to simulate the effect of backfill during fracture propagation simulations. Several aspects of the modelling techniques were investigated such as the effect of the backfill model size and particle size, as well as various backfill material properties. The effect of each of these parameters was quantified through the effect on the steady state fracture velocity of the model, and effect on the shape of the fracture resistance curve. The constant CTOA model was combined with the SPH model to calculate steady-state fracture velocities for an API X80 and X100 steel with various geometries. This was done to generate a database of fracture resistance data. The fracture resistance data was used to determine the arrest CTOA for various materials and geometries. Using the fracture resistance data, an equation was determined to calculate the arrest CTOA required for a given material, geometry, and operating pressure and backfill. This equation was compared with two other previous arrest CTOA models. The predictions were shown to agree well with X100 experimental data. The arrest methodology was further validated through examining a recent full scale burst test performed on a grade 550 pipe. The CTOA derived fracture resistance curves were shown to estimate the fracture velocity of each of the pipe sections better than the original TCM.
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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 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".