An inverse finite element approach for the evaluation of the hot torsion test

The hot torsion test enables the analysis and simulation of hot forming behaviour up to large deformations. The emergence of strain, strain rate and temperature gradients in the specimen result in complex material response. For the development of an advanced evaluation, experimental torsion tests were carried out in a Gleeble 3800. As a basis for the evaluation, two finite element models were set-up in ABAQUS®. The determination of the underlying Hensel-Spittel constitutive model was done by an inverse analysis of experimental torsion data. Starting from initial values, the parameter set with the smallest deviation between numerical and experimental data is searched for. This optimisation problem was solved by an implementation of the Nelder-Mead algorithm. The experimental results revealed certain test conditions lead to a local instability. This results in flow localisation, due to a spatially confined temperature gain. The classical analytical evaluation method can then no longer be carried out reliably. The evaluation carried out using an inverse analysis showed good agreement with experimental results. A comparison of the determined material parameters with literature data from compression tests also were in good agreement.