Jaremenko Christian, Affronti Emanuela, Maier Andreas, Merklein Marion
Pattern Recognition Lab, Friedrich-Alexander-Universität Erlangen-Nürnberg Martensstr. 3, 91058 Erlangen, Germany.
Institute of Manufacturing Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstr. 13, 91058 Erlangen, Germany.
Materials (Basel). 2018 Oct 3;11(10):1892. doi: 10.3390/ma11101892.
The forming limit curve (FLC) is used in finite element analysis (FEA) for the modeling of onset of sheet metal instability during forming. The FLC is usually evaluated by achieving forming measurements with optical measurement system during Nakajima tests. Current evaluation methods such as the standard method according to DIN EN ISO 12004-2 and time-dependent methods limit the evaluation range to a fraction of the available information and show weaknesses in the context of brittle materials that do not have a pronounced constriction phase. In order to meet these challenges, a supervised pattern recognition method was proposed, whose results depend on the quality of the expert annotations. In order to alleviate this dependence on experts, this study proposes an unsupervised classification approach that does not require expert annotations and allows a probabilistic evaluation of the onset of localized necking. For this purpose, the results of the Nakajima tests are examined with an optical measuring system and evaluated using an unsupervised classification method. In order to assess the quality of the results, a comparison is made with the time-dependent method proposed by Volk and Hora, as well as expert annotations, while validated with metallographic investigations. Two evaluation methods are presented, the deterministic FLC, which provides a lower and upper limit for the onset of necking, and a probabilistic FLC, which allows definition of failure quantiles. Both methods provide a necking range that shows good correlation with the expert opinion as well as the results of the time-dependent method and metallographic examinations.
成形极限曲线（FLC）在有限元分析（FEA）中用于模拟板材成形过程中的失稳起始。FLC通常通过在 Nakajima 试验期间使用光学测量系统进行成形测量来评估。当前的评估方法，如根据 DIN EN ISO 12004-2 的标准方法和与时间相关的方法，将评估范围限制在可用信息的一小部分，并且在没有明显缩颈阶段的脆性材料的情况下存在缺陷。为了应对这些挑战，提出了一种监督模式识别方法，其结果取决于专家注释的质量。为了减轻对专家的这种依赖，本研究提出了一种无监督分类方法，该方法不需要专家注释，并允许对局部颈缩的起始进行概率评估。为此，使用光学测量系统检查 Nakajima 试验的结果，并使用无监督分类方法进行评估。为了评估结果的质量，将其与 Volk 和 Hora 提出的与时间相关的方法以及专家注释进行比较，同时通过金相研究进行验证。提出了两种评估方法，确定性FLC，它为颈缩的起始提供下限和上限，以及概率性FLC，它允许定义失效分位数。这两种方法都提供了一个颈缩范围，该范围与专家意见以及与时间相关的方法和金相检查的结果显示出良好的相关性。
