Variation of deep drawing steel grades’ properties in dependency of the stress state and its impact on FEA
Variation of deep drawing steel grades’ properties in dependency of the stress state and its impact on FEA
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深冲钢种性能随应力状态的变化及其对有限元分析的影响
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发表时间：
2011
期刊：
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通讯作者：
M. Merklein
中科院分区：
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作者：
Vera Goedel;M. Merklein
在工业钣金成形工艺中，由于对雄心勃勃的设计和轻质结构的要求，零件的复杂性在过去十年中有所增加。由于成形工艺通常布置在可行性极限附近，工艺参数和材料性能的微小变化可能导致批量生产中废品率增加。在计算机工艺设计中考虑变参数是普遍可行的，但特别是在材料性能变化的数值模拟中如何更接近实际，还没有得到全面的研究。在所谓的随机模拟中考虑的变化参数通常限于可以在单轴拉伸试验中确定的力学性能。由于在复杂钣金件的成形过程中会出现不同的应力状态，因此必须详细研究不同成形条件下的批量变化。在这项工作中，提出了一个基本的调查，考虑在不同的应力状态下的批次变化。三个线圈相同的钢种，温和的深冲钢DX56，其特征在于实验，以调查的三个批次之间的应力的分散带代表材料的变化接近现实。为此，在单轴应力条件下和双轴应力条件下确定了流动行为。此外，双轴应力条件下的测试结果导致批次特定双轴应力点，其代表根据Hill 90的屈服轨迹插值的另一个参考点。通过实验确定了三个批次的成形极限图，以重现颈缩开始的分散性。基于实验结果，三批特定的材料有限元模拟模型的准备和作为输入参数的数值成形模拟。采用交叉凹模几何结构，可以在四个参考点上调整不同的应力状态，覆盖单轴和双轴应力状态之间的应力状态，即平面应变区。在参考点范围内，评估了材料性能变化对失效风险的影响。
In industrial sheet metal forming processes the complexity of parts has been increased within the last decade due to the demands on ambitious designs and lightweight construction. As the forming processes are often laid out near the limit of feasibility, small variations of process parameters and materials’ properties may lead to an increased scrap rate in serial production. The consideration of varying parameters in the computerized process design is generally realizable, but especially the modelling of the material properties’ variation in numerical simulation close to reality is not investigated comprehensively yet. The varying parameters considered in a so called stochastic simulation are often limited to the mechanical properties, which can be determined within the uniaxial tensile test. As within the forming process of a complex sheet metal part different stress states occur, the batch variation under different forming conditions has to be investigated in detail. Within this work a basic investigation for the consideration of the batch variation under different stress states is presented. Three coils of the same steel grade, the mild deep drawing steel DX56, are characterised experimentally in order to investigate the scatter band of the stresses between the three batches representing material variation close to reality. For this the flow behaviour is determined under uniaxial stress condition and under biaxial stress condition. Furthermore the results of the tests under biaxial stress condition lead to a batch specific biax-stress-point, which represents a further reference point for the yield locus interpolation according to Hill 90. The forming limit diagrams are determined experimentally for the three batches in order to reproduce scattering of the onset of necking as well. Based on the experimental results, three batch specific material models for FE-simulation are prepared and used as input parameters for numerical forming simulations. Using the cross die geometry with two different initial blank geometries, different stress states can be adjusted in four reference points, covering the stress states between uniaxial and biaxial stress condition, thus, the plane strain area. Within the reference points, the effect of materials’ properties variation on the risk of failure is evaluated.