Degradation of Mechanical Properties for Polyethylene by Small-Deformation Damage
Bibliographic record
Abstract
Polyethylene (PE) has now been widely used to make plastic pipe for gas transportation. Because of its excellent ductility, processes for repair and maintenance of PE pipe allow squeeze-flattening the pipe to reduce the gas flow. Our previous study has shown that stretch of PE, even at a low strain level, can cause damage of the material, and significance of the damage depends on the strain rate. This paper presents results from a follow-up study, to investigate the possibility of quantifying the influence of damage on the mechanical properties. Coupon specimens used in this study have the same geometry as that used previously. Each specimen was tested twice. The 1st test was to introduce the damage, by stretching the specimen at a crosshead speed of 1 mm/min; the 2nd test to characterize the influence of the damage on the mechanical properties, by stretching the specimen at 1 μm/min. The two crosshead speeds were chosen because the former (1 mm/min) is known to introduce much more damage than the latter (1 μm/min) at a same strain level. Therefore, change in mechanical properties observed from the 2nd test should mainly come from the damage generated in the 1st test. To avoid influence of viscous recovery from the 1st test on the results from the 2nd test, the two tests were conducted more than one month apart. Test results show that even by stretching the specimen to a strain level below the yield point in the 1st test (i.e. with the strain less than 0.1), damage introduced to the specimen can cause a detectable decrease in the mechanical properties, such as the tangent modulus at the strain 0.01 and the stress response at the strain 0.1, from the 2nd test. The results also show that the rate of decrease of the above values with the increase of strain becomes significant when the strain level introduced in the 1st test is above the yield point. By stretching the specimen to a strain level about 0.5 in the 1st test, though yet to cause apparent necking or stress whitening, the tangent modulus and the stress response in the 2nd test are decreased by about one-third of the values for the virgin specimen. This amount of change is significant and should not be ignored for long-term applications such as for gas transportation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".