科研之友
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摘要
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 degrees C within 15 min of start-up, and ensuring temperature uniformity throughout the gage length within 8 degrees C. The low-cost device also makes isothermal testing possible at strain rates higher than corresponding tests in air. %26lt;br%26gt;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 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). %26lt;br%26gt;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 degrees C with a strain rate of 0.001/s. The inflected stress-strain curve observed in compression at room temperature disappeared between 125 and 150 degrees C, corresponding to the suppression of twinning, and suggesting a simple method for identifying the deformation mechanism transition temperature. The temperature-dependent behaviors of selected advanced high strength steels (TWIP and DP) were revealed by preliminary tests at room temperature, 150 and 250 degrees C.
- 出版日期2012-11
