| Abstract: | The influence of strain rate on the stress-strain curve of materials showing yield point phenomenon are determined in the range of small strains and high strain rates by means of the indirect impact tension test. With increasing deformation velocity, the Lüders strain is found to increase considerably. The stress reduction after reaching the upper yield point, is not abrupt and takes place gradually with increasing strain. These phenomena are investigated on Armco iron, on the tempered steel 42 CrV 6, on pure tantalum and tungsten alloys. A simple mechanical model is introduced which shows that the Lüders front velocity increases with strain rate approaching asymptotically the value of the plastic wave velocity as an upper limit. With this restriction, the local strain within the Lüders band must increase by increasing the rate of elongation of the tensile specimen. The Lüders strain could be estimated quantitatively as a function of strain rate. The model describes also the stress-strain function after reaching the upper yield point considering the limited stiffness of the test arrangement. |
