An Elevated-Temperature Tension-Compression Test and Its Application to Mg AZ31B
Bibliographic record
Abstract
Many metals, particularly ones with HCP crystal structures, undergo deformation by combinations of twinning and slip, the proportion of which depends on variables such as temperature and strain rate.Typical techniques to reveal such mechanisms rely on metallography, x-ray diffraction, or electron optics.Simpler, faster, less expensive mechanical tests were developed in the current work and applied to Mg AZ31B.An apparatus was designed, simulated, optimized, and constructed to enable the large-strain, continuous tension/compression testing of sheet materials at elevated temperature.Thermal and mechanical FE analyses were used to locate cartridge heaters, thus enabling the attainment of temperatures up to 350 o C within 15 minutes of start-up, and ensuring temperature uniformity throughout the gage length within 8 o C. The low-cost device also makes isothermal testing possible at strain rates higher than corresponding tests in air.Analysis was carried out to predict the attainable compressive strains using novel finite element (FE) modeling and a single parameter characteristic of the machine and fixtures.The limits of compressive strain vary primarily with the material thickness and the applied-side-force-to-material-strength ratio.Predictions for a range of sheet alloys iii with measured buckling strains from -0.04 to -0.17 agreed within a standard deviation of 0.025 (0.015 excluding one material that was not initially flat).In order to demonstrate the utility of the new method, several sheet materials were tested over a range of temperatures.Some of the data obtained is the first of its kind.Magnesium AZ31B sheets were tested at temperatures up to 250 o C with strain rate of 0.001/s.The inflected stress-strain curve observed in compression at room temperature disappeared between 125 o C and 150 o C, corresponding to the suppression of twinning, and suggesting a simple method for identifying the deformation mechanism transition temperature.The temperature-dependent behavior of selected advanced high strength steels (TWIP and DP) was revealed by preliminary tests at room temperature, 150 o C and 250 o C. For Mg AZ31B alloy sheets, the curvature of compressive stress-strain plots over a fixed strain range was found to be a consistent indicator of twinning magnitude, independent of temperature and strain rate.The relationship between curvature and areal fraction of twins is presented.Transition temperatures determined based on stress-strain curvature were consistent with ones determined by metallographic analysis and flow stresses, and depended on strain rate by the Zener-Hollomon parameter, a critical value for which was measured.The transition temperature was found to depend significantly on grain size, a relationship for which was established.Finally, it was shown that the transition temperature can be determined consistently, and much faster, using a single novel -Step-Temperature‖ test.iv
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 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 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 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".