Reuther Franz, Lieber Thomas, Heidrich Jürgen, Kräusel Verena
Fraunhofer Institute for Machine Tools and Forming Technology IWU, 09126 Chemnitz, Germany.
Materials (Basel). 2021 Apr 9;14(8):1882. doi: 10.3390/ma14081882.
Forming 7000-series aluminum alloys under elevated temperatures is particularly attractive due to their increased formability. To enable process design by finite element simulation for hot forming, strain-based criteria, such as temperature-dependent forming limit diagrams (TFLD), can be consulted to assess forming feasibility. This work numerically investigates the extent to which in-plane experimental concepts with partial inductive heating are suitable for detecting discrete failure points in TFLD. In particular, an alternative to the currently widely used thickness-reduced specimen geometries was created for cruciform specimens under biaxial tension. First, the temperature-dependent and strain-rate-dependent flow behavior was investigated for AA7075 under uniaxial tension. A heat source model for partial inductive heating was inversely parameterized based on heating experiments. Subsequently, the test procedures were simulated with different specimen geometries under discrete strain conditions. Different concepts were discussed for deriving a suitable specimen shape for the biaxial tension case, and the influence of different notch and slot forms were shown. The simulations showed that partial inductive heating was suitable to induce failure situations, thus creating TFLDs. For the biaxial tension case, a sufficiently large temperature gradient was required to use cruciform specimens without thickness reduction.
由于7000系列铝合金在高温下的可成形性增强，因此在高温下成形具有特别的吸引力。为了通过有限元模拟进行热成形工艺设计，可以参考基于应变的准则，如与温度相关的成形极限图（TFLD），来评估成形的可行性。本文通过数值模拟研究了采用局部感应加热的平面内实验概念在多大程度上适用于检测TFLD中的离散失效点。特别是，针对双轴拉伸下的十字形试样，创建了一种替代当前广泛使用的厚度减小试样几何形状的方案。首先，研究了AA7075在单轴拉伸下与温度和应变速率相关的流动行为。基于加热实验对局部感应加热的热源模型进行了反向参数化。随后，在离散应变条件下，对不同试样几何形状的测试过程进行了模拟。讨论了为双轴拉伸情况推导合适试样形状的不同概念，并展示了不同缺口和狭槽形式的影响。模拟结果表明，局部感应加热适用于引发失效情况，从而创建TFLD。对于双轴拉伸情况，需要足够大的温度梯度才能使用不减小厚度的十字形试样。
