| Popis: |
Investigations of metal materials properties were always based on preforming tests, for confirmation of mechanical properties mainly tensile tests were used. However, due to complicated state of stress after neck occurrence, these cannot be used for practical application at industrial forming processes. That's why plastometric tests (torsion, press)are further utilized, their outcomes are curves of stress-strain dependence. After applications of large strains tests always result in curve with Sigmap maximum stress value corresponding to the peak strain value Ethap. Reaching of this strain value induces (dynamic) re-crystallization or start of recovery. It is mostly one single point on the stress-strain curve, which can be defined unambiguously and mathematically described depending on the basic parameters. Single curves may vary in accordance with various ways of plotting, basic parameters (temperature T, strain Etha, and the strain rate Etha''), additional conditions (chemical composition influence and history of the material - residual strain after incomplete re-crystallization or recovery), structure influence (phases portions, grain size) etc. The paper is focused on various methods of peak stress description on the basisi of Gleeble plastometer tests results and Plane Strain Compression tests. |
