Anisotropic failure criterion for evaluation of local necking after nonlinear deformation history in sheet metal forming processes

成形性预测是板料成形模拟的重要内容之一。在工业应用中的通用标准是成形极限曲线（FLC）。FLC的最大优势是结合ISO标准对模拟或测量数据进行简单的解释。然而，传统的FLC仅限于几乎线性和不间断的应变路径，即具有非线性应变增量的变形历史与FLC的预测相比往往导致很大的差异。Volk提出了一种唯象的方法，即广义成形极限概念（Generalized Forming Limit Concept，GFLC），用于预测任意变形历史下的局部颈缩。目前GFLC还没有考虑各向异性材料的行为，本研究项目的主要重点是根据轧制方向（各向异性）和成形历史对成形极限进行实验表征。实验将主要在DFG（INST 95/1268-1）资助的通用试验机BUP 1000上进行。基于实验数据库的参数化的应变路径和扩展的元模型与各向异性材料的行为发生。最后，通过对材料影响的识别和对材料族尺度方法的推导，完成了本课题的研究，预期的结果使得通过考虑各向异性材料行为来评估非线性应变路径成为可能。

The prediction of formability is one of the most important tasks in sheet metal process simulation. The common criterion in industrial applications is the Forming Limit Curve (FLC). The big advantage of FLCs is the easy interpretation of simulation or measurement data in combination with an ISO standard for the experimental determination. However, the conventional FLCs are limited to almost linear and unbroken strain paths, i.e. deformation histories with non-linear strain increments often lead to big differences in comparison to the prediction of the FLC. Volk published a phenomenological approach, the so-called Generalized Forming Limit Concept (GFLC), to predict the localized necking on arbitrary deformation history with unlimited number of non-linear strain increments. Anisotropic material behavior is not considered in the GFLC so far.The main focus of the proposed research project is the experimental characterization of the forming limits depending on the rolling direction (anisotropy) and the forming history. The experiments will be performed mainly on the universal testing machine BUP1000, funded by DFG (INST 95/1268-1). Based on the experimental database a parameterization of the strain paths and an expansion of the metamodel with the anisotropic material behavior takes place. Finally, the identification of the material influence on the developed procedure and derive of a scaling approach for material families complete the research project.The expected results enable the evaluation of non-linear strain path by the consideration of anisotropic material behavior.