Evaluation of Experimental Forming Limit Curves and Investigation of Strain Rate Sensitivity for the Start of Local Necking
Evaluation of Experimental Forming Limit Curves and Investigation of Strain Rate Sensitivity for the Start of Local Necking
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局部颈缩开始时实验成形极限曲线的评估和应变率敏感性的研究
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
P. Hora
中科院分区：
文献类型：
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作者：
W. Volk;P. Hora
板料成形中的失效预测通常是通过计算成形极限曲线来实现的。到目前为止，FLC测定是使用Nakajima或Marciniak试验装置的失效样本进行的。标准方法通过考虑开裂的发生来确定失效，而不考虑Nakajima试验的时间连续记录的可能性。因此，以这种方式评估的成形极限曲线通常是“实验室依赖性的”，并且对于相同的材料偏离很大。这一贡献提出了一种算法，一个全自动和时间依赖性的确定开始塑性不稳定的基础上的物理效应。该算法是基于基于位移场的应变分布的评价，该位移场通过光学测量进行评价并被视为有限元计算的网格。临界变形状态，然后定义的2D考虑的应变分布和它们的时间导数使用的数值评估程序检测开始的本地化。所提出的算法的有效性将被用于Numisheet'08 Benchmark-1与Nakajima测试的不同材料。此外，还讨论了应变率敏感性对局部颈缩起始失稳的影响。结果表明，应变速率敏感性在板料成形模拟中起着不可忽视的重要作用。
The failure prediction in sheet metal forming is typically realized by evaluating the so called forming limit curves (FLC). Up to now, the FLC determination was performed with failed specimens of Nakajima or Marciniak test setups. Standard methods determine the failure by considering the occurrence of cracking and do not consider the possibility of time continuous recording of the Nakajima test. Consequently forming limit curves which have been evaluated in such way are often “laboratory dependent” and deviate for identical materials significantly. This contribution presents an algorithm for a fully automatic and time-dependent determination of the beginning plastic instability based on physical effects. The algorithm is based on the evaluation of the strain distribution based on the displacement field which is evaluated by optical measurement and treated as a mesh of a finite element calculation. The critical deformation states are then defined by 2D-consideration of the strain distribution and their time derivatives using a numerical evaluation procedure for detecting the beginning of the localization. The effectiveness of the proposed algorithm will be presented for different materials used for the Numisheet’08 Benchmark-1 with Nakajima test. Additionally the effect of strain rate sensitivity on the beginning instability of local necking is discussed. It can be shown that the strain rate sensitivity is from major importance and should not be neglected for the forming simulation of sheet metal materials.