Flow stress measuring by use of cylindrical compression test and special application to metal forming processes

In recent years the finite-element-method (FEM) simulation has become applicable for the development, design and optimisation of metal forming processes. To obtain accurate results within the simulation the exact description of the flow stress k f during the process is essential. The implementation of the flow curve into FE-packages can be realised through different methods. Using the measured data in tabular form seems to be the easiest way, but special interpolation methods are necessary and extrapolation is strictly forbidden. Hence the exact flow stress measurement up to highest strain rates (between 0.0001 and 300/s) to simulate industrial processes like rolling or extrusion is essential. This paper presents actual studies in the field of high-speed testing by use of a servohydraulic testing system in a temperature range between room temperature and 1300 °C. Furthermore the use of material models to describe the material behaviour is getting more and more popular. Therefore hot compression tests must be carried out to determine the necessary parameters for reliable prediction. Specifically for aluminium alloys, where homogeneous deformation in the temperature range above 300 °C is not possible at present, new strategies for the determination of the material models have been developed. The compression tests are deliberately performed under sticking conditions to obtain strong gradients of the forming and microstructure parameters within a sample. The model equations are then adapted by consideration of the local parameters. Finally an optimisation coupled with an FEM program is applied to the models.