A Comparative Study of Ke Factor in Design by Analysis for Fatigue Evaluation
Bibliographic record
Abstract
ASME Section III Design by Analysis rules provide a “Simplified Elastic-Plastic Analysis” approach for the fatigue usage evaluation when the primary plus secondary stress range exceeds the limit of 3Sm. A penalty factor Ke is applied to the alternating peak stress calculated by assuming elastic material behavior. There is general consensus that the Ke factor determined using current code equations can be overly conservative for some conditions, and can lead to severe design limitations. The ASME code committees have been actively working on revising the Ke equations. The work in this paper intends to assess the conservatism of the Ke procedure in current ASME NB-3228.5, and to evaluate the two proposed alternative ASME Code Ke procedures through a comparative study. The evaluation focuses on the Ke procedure related to the effect of through-wall temperature gradient induced stresses on fatigue life for austenitic stainless steel. The conservatism of current ASME NB-3228.5 rules for the Ke factor is demonstrated through the comparison of predicted fatigue life with the test result of a stainless steel stepped pipe. In view of the technical background that the Ke factor represents the ratio of the actual strain range to the elastically calculated strain range, the theoretically accurate Ke factor can be calculated from elastic and elastic-plastic analyses. This directly calculated Ke factor is found to be in good agreement with the fatigue life from the test. A comparative study of procedures for calculating the Ke factor using current ASME NB-3228.5 rules and its counterparts in various codes is then conducted. B31.7 code, French RCC-M code and Japanese JSME code are considered. The two proposed alternative ASME Code Ke methodologies are evaluated. The differences in calculated Ke values are illustrated through the sample stepped pipe problem with various thermal transients. The directly calculated Ke factor using elastic and elastic-plastic analyses is used as reference value for comparison and conservatism assessment.
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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 | 0.015 | 0.048 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.004 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".