Internal variable model describing high temperature plastic behaviour of metallic materials in a wide range of strain rates

The internal variable model of Follansbee and Kocks (FK) describes the plastic behavior of metallic materials by using two internal variables: the threshold stress and the thermal activated parameter of flow stress. The model has been applied to a wide range of metallic alloys, like steels. The original procedure to find the internal variables is quite complex, and a new straightforward method has been proposed to find the temperature and strain rate dependence of the two internal variables. The method is first applied to a large grained OFHC copper deformed through tensile tests from room temperature to 700°C with strain rates between 10-4 and 10-2 s-1, for the results can be compared to the original FK results on copper. The internal variable model is useful since it allows the introduction of other internal variables. A new variable and corresponding evolution equation have been introduced to model the flow stress when dynamic recrystallisation (DRX) occurs. After having analyzed the good matching between the results from the original FK procedure and the new one, the capability of predicting the flow behavior of copper in the range of conditions typically experienced in thermo-mechanical processing is investigated through high strain rate compression tests and impact tests, performed by a thermo-mechanical simulator Gleeble and a SHPB testing rig, respectively. Preliminary results of this investigation are reported.