Problems associated with use of the logarithmic equivalent strain in high pressure torsion

6th International Conference on Nanomaterials by Severe Plastic Deformation

材料科学;化学

Jonas, J.J.^1 ; Aranas, C.^1

Materials Engineering, McGill University, 3610 University St., Montreal H3A 0C5, Canada^1

关键词: Conjugacy;    Equivalent strains;    High pressure torsions;    Rate sensitivity;    Von Mises;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/63/1/012048/pdf
DOI  :  10.1088/1757-899X/63/1/012048

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

The logarithmic "equivalent" strain is frequently recommended for description of the experimental flow curves determined in high pressure torsion (HPT) tests. Some experimental results determined at -196 and 190 °C on a 2024 aluminum alloy are plotted using both the von Mises and logarithmic equivalent strains. Three types of problems associated with use of the latter are described. The first involves the lack of work conjugacy between the logarithmic and shear stress/shear strain curves, a topic that has been discussed earlier. The second concerns the problems associated with testing at constant logarithmic strain rate, a feature of particular importance when the material is rate sensitive. The third type of problem involves the "history dependence" of this measure in that the incremental logarithmic strain depends on whether the prior strain accumulated in the sample is known or not. This is a difficulty that does not affect use of the von Mises equivalent strain. For these reasons, it is concluded that the qualifier "equivalent" should not be used when the logarithmic strain is employed to describe HPT results.