A Parametric Study of Variable Crack Initiation Criterion in XFEM on Pipeline Steel
Bibliographic record
Abstract
Abstract The integrity decisions for cracked pipelines can be made based on the conventional Finite Element Method (FEM). However, it is extremely time-consuming due to the requirement of remeshing to continuously conform to the geometric discontinuities as the crack propagates. The more recently developed Extended Finite Element Method (XFEM) provides a more robust approach in which a crack can propagate through the finite element analysis mesh and thus alleviates the requirement for remeshing. However, the current criteria for crack initiation and propagation in XFEM framework have not been calibrated to pipeline steels. The current built-in criterion in Abaqus assumes a fixed value as the damage strain. Crack initiation occurs after this strain is exceeded. However, the accuracy of numerical crack propagating path is questionable, especially in a side-grooved single edge notched tension (SENT) model. Faster crack initiation at specimen side over the center conflicts with the actual crack propagating path obtained from a physical test. This paper develops a new crack initiation criterion which defines a variable damage strain as a function of the stress configuration at the crack tip. The criterion is modified from the Mohr-Coulomb fracture criterion as a function of stress triaxiality and Lode angle parameters. The damage strain exponentially decreases as the stress triaxiality increases. This paper presents a parametric study on the effects of material parameters considered in the criterion on the development of damage strain locus. The new crack initiation criterion is applied to a side-grooved SENT model, in which the corresponding failure mechanism is defined by the user’s subroutine UDMGINI in Abaqus.
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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) | 0.000 | 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 | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".