Improved FEA of deep drawing at elevated temperatures of magnesium sheet materials based on a realistic modelling of their formability at process conditions

前一个项目的目标是改进普通镁片材料AZ31的温度依赖性硬化和软化行为模型，以便更准确地通过高温深拉成形进行有限元分析。通过矩形杯拉深过程的仿真结果与实验结果的比较，对改进模型的质量进行了评价。在该工艺的有限元分析中使用确定的流量曲线，该曲线真实地再现了材料的硬化和软化过程，与常规外推的连续增加流量曲线相比，其精度更高。然而，由于关键材料点处的成形路径超出了成形极限曲线的有效范围，因此无法对成形件的变形局部化和随后的裂纹形成进行数值预测。新项目的目标是表征镁板材料AZ31在比成形极限曲线更宽的应力和应变状态范围内的成形性。表征将借助基于剪切拉伸试样的剪切拉伸试验的钣金成形性测定方法，结合基于在工艺相关温度下对腰板坯进行拉伸试验的常规成形极限曲线测定方法进行。所获得的数据将集成到高温下深拉深的热力学模拟中。因此，应描述应力状态和温度对所研究材料成形性的影响。此外，还应研究在确定了与工艺相关的应力状态和温度的成形性描述后，能否在工艺模拟中实现更好的成形性预测。根据项目结果，镁片材料的改进材料建模以及通过成形加工的工艺极限扩展有望实现。

The objective of the preceeding project was an improved model of temperature-dependent hardening and softening behaviour of a common magnesium sheet material AZ31 for a more accurate FEA of its forming via deep drawing at elevated temperatures. The quality of the improved model was assessed based on a comparison between simulation and experimental results of a deep drawing process on rectangular cups. The use of the determined flow curve, which realistically reproduces both hardening and softening of the material, in the FEA of the process leads to its higher accuracy compared to the FEA of the process with a conventionally extrapolated continuously increasing flow curve. However, numerical prediction of a deformation localisation and subsequent crack formation in the formed part was not possible as the forming path at the critical material point was outside the validity range of the forming limit curve.The objective of the new project is characterisation of formability of the magnesium sheet material AZ31 in a range of stress and strain states wider than that of the forming limit curve. The characterisation is to be carried out with the help of a method for determination of sheet metal formability based on shear-tensile tests on shear-tensile specimens combined with a method for determination of conventional forming limit curves based on stretching tests on waisted sheet blanks at process-relevant temperatures. The obtained data is to be integrated into a thermo-mechanical simulation of deep drawing at elevated temperatures. Thus, the influence of the stress state and temperature on formability of the studied material is to be described. Furthermore, it should be investigated if an improved formability prediction in the process simulation can be achieved with the determined formability description for process-relevant stress states and temperatures. With project results, an improved material modelling for magnesium sheet materials as well as a process limit extension of their processing via forming are expected to be achieved.