Dehnungsabhängige Elastizitätsmodule und weitere bestimmende Faktoren auf die Rückfederung bei der Blechumformung

There is still great interest in the sheet metal processing industry in a scientifically based, reliable prediction of the spring back. The prediction accuracy of the spring back simulation has been improved significantly in recent years and enables simulation-supported tool compensation for soft deep-drawing steels.Despite the further developments and the intensive efforts to adequately model the spring back simulation, it is still not possible to make an accurate and reliable prediction of the spring back of the formed component parts in all cases. Especially with aluminum and high-strength steels there are still problems with the exact prediction of the spring back behavior.The reason of these often unsatisfactory results of the spring back prediction can be found simultaneously in several sub-aspects of modeling and implementation. These sub-aspects include variables such as the modulus of elasticity, the kinematic hardening and the coefficient of friction. A basic prerequisite for adequate modeling of the elastic material properties is their reliable experimental determination.Despite the supposed simplicity of corresponding test trials, experiments repeatedly produce highly scattered and contradictory results, which on the one hand are often related to the metrological requirements and an incorrect evaluation of the tests, but on the other hand also with unexplained scattering of the material properties in the sheet. The focus of the project is on the experimental determination of the elastic slope.Three different methods of strain measurement are examined. However, questions regarding evaluation methods for determining the elastic slope from the measurement data and the evaluation of the influence of the elastic slope on the return in comparison to other influencing factors such as kinematic hardening and friction were also investigated.