Development of a plane strain-test method for tubular semi-finished parts and a wide range of strain-rates

成形过程的方法规划通常使用基于仿真的设计，这需要关于材料弹塑性行为的详细信息。现有针对平板金属半成品的有限元模拟基本试验和建模方法，但对管状半成品的模拟应用有限。现有的管状半成品表征试验（如环拉伸试验、管爆裂试验）在工业实践中几乎没有被接受，但主要使用现有的基于平板金属制品试验的材料卡。这导致在模拟以下成形过程时出现相当大的误差，并且基于模拟的工艺设计的潜力没有得到充分利用。因此，本研究项目的目的是开发一种新的管状半成品材料检测方法，以弥补现有检测方法存在的不足。面向过程的材料性能数值模拟需要在所考虑过程的特征条件下进行材料测试。在管状半成品成形的背景下，液压成形是除弯曲和预成形步骤外的主要制造工艺。对于这种技术，平面应变状态和10/s数量级的应变速率是特别重要的。因此，研究项目的总体目标是在这种应变状态和高应变率下，开发、试验和验证管状半成品材料特性的测试策略。通过应用所提出的方法，与目前的技术水平相比，对材料行为进行更精确的建模，从而对管状半成品的成形进行更精确的数值模拟成为可能。对管状半成品进行广泛和局部解决的表征，可以识别晶格类型，纹理，应力状态和应变率灵敏度之间的相互关系。由于对材料的微观力学过程有了更深入的了解，模型质量将得到显著提高。钢合金C45将作为一个简单的（体心立方）模型材料进行研究，这可以清楚地了解基本的相关性。随后，测试方法转移到奥氏体（面心立方）铬镍钢（1.4301），用于工业排气系统领域。

Method planning for forming processes often uses simulation-based designs, which require detailed information about the elastic-plastic material behavior. Established basic tests and modelling approaches for finite element (FE) simulation exist for flat sheet metal semi-finished products, but the transfer to tubular semi-finished products is limited. Existing tests for the characterization of tubular semi-finished products (e.g. ring tensile test, tube burst test) have hardly been accepted in industrial practice, but existing material cards based on the testing of flat sheet metal products are mainly used. This results in a considerable error in the simulation of the following forming processes and the potential of a simulation-based process design is not fully exploited. Therefore, the aim of this research project is to develop a new method for material testing of tubular semi-finished products, which will compensate for the existing disadvantages of current testing methods.The process-oriented numerical modelling of material behavior requires material testing under the conditions that are characteristic for the regarded process. In the context of the forming of tubular semi-finished products, hydroforming is the dominating manufacturing process in addition to bending and preforming steps. For this technology the plane strain state and strain rates in the order of several 10/s are particularly relevant. The overall objective of the research project is therefore the development, trial and validation of a testing strategy for the material characterization of tubular semi-finished products under this strain state and at high strain rates. By applying the presented methodology, a much more exact modelling of the material behavior and thus a more precise numerical modelling of the forming of tubular semi-finished products becomes possible compared to the state of the art. An extensive and locally resolved characterization of the tubular semi-finished products allows an identification of the interrelations between lattice type, texture, stress state and strain rate sensitivity. Due to the resulting deeper understanding of the micromechanical processes in the material, a significant improvement of the model quality will result. The steel alloy C45 will be investigated as a simple (body-centered cubic) model material, which allows a clear understanding of the basic correlations. Subsequently, the test methodology is transferred to an austenitic (face-centered cubic) chrome-nickel steel (1.4301), which is used in the industrial context in the area of exhaust systems.