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New experimental approach for yield loci determination using a modified Nakajima setup

使用修改后的 Nakajima 设置确定产量位点的新实验方法

基本信息

批准号：
363839128
负责人：
Professor Dr.-Ing. Wolfram Volk
金额：
--
依托单位：
Lehrstuhl für Umformtechnik und Gießereiwesen
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/363839128?language=en
关键词：
New experimental approach yield loci

项目摘要

In the state of the art the Nakajima test is used to determine die forming limit of sheet metal. In the common test setup, consisting of a spherical punch, a die and a blank holder, only the strains in the sheet are measured. The aim of the research project is the development of a method for the experimental determination of stress states by use of a modification of the Nakajima test. For this purpose, different measurement concepts are developed for the detection of the normal pressure between the apex area of the punch and different tailored specimens by means of a simulation and a calibrated test rig. The high strength steel DP600 is used as a test material. On the basis of the experiments as well as the virtual experiments with specimens, which have different widths, a mathematical method is designed for differentiation of the measured normal pressure into the membrane stresses. This approach takes into account the complete punch stroke and thus the entire forming history of the test sheet. By means of the resulting knowledge, it is possible to determine flow curves or yield loci for sheet metal, at different stress states in the first quadrant of the stress space, as well as for each strain state of the deformation history up to the determination of the local necking. The methodology is validated by using of prescale foil, which can measure the pressure, and the bulge test. Finally, experimental yield loci are determined exemplary. The Nakajima tests, which are required in the research project, are determined on the BUP1000 universal sheet metal testing machine procured within the scope of the DFG large instrument application. The new approach to determine the yield locus offers the possibility to understand the plastic material behavior better, to compare numerical material models with actual material parameter, and to develop new yield function approaches. Performing all the necessary tests on one test machine and one experimental setup, which already finds a wide application for the determination of the forming limit, minimizes the extensive effort required for the determination of yield loci.The main objectives of the research project include:1.Construction of measuring concepts and a calibrated test rig2.Derivation of calibration function depending on the different specimen widths3.Development of a mathematical method for the decomposition of the normal pressures in membrane stresses4.Determination of flow curves and yield loci by means of the membrane equation

在现有技术中，Nakajima试验用于确定金属板的模具成形极限。在由球形冲头、凹模和坯料保持器组成的普通测试装置中，仅测量板中的应变。该研究项目的目的是开发一种方法，通过使用修改的Nakajima测试来实验确定应力状态。为此，开发了不同的测量概念，用于通过模拟和校准试验台检测冲头顶点区域与不同定制样品之间的法向压力。高强度钢DP600被用作测试材料。在实验和不同宽度试件虚拟实验的基础上，设计了一种将实测法向压力微分为薄膜应力的数学方法。这种方法考虑了整个冲压行程，从而考虑了测试板的整个成形历史。通过所得的知识，可以确定金属板在应力空间的第一象限中的不同应力状态下的流动曲线或屈服轨迹，以及直到确定局部颈缩的变形历史的每个应变状态。利用可测量压力的预标箔和胀形试验对该方法进行了验证。最后，实验屈服位点被确定为示例。在DFG大型仪器应用范围内采购的BUP 1000通用钣金试验机上确定了研究项目中所需的Nakajima试验。确定屈服轨迹的新方法提供了更好地理解塑性材料行为、比较数值材料模型与实际材料参数以及开发新的屈服函数方法的可能性。在一台试验机和一个实验装置上进行所有必要的试验，这已经广泛应用于确定成形极限，最大限度地减少了确定屈服轨迹所需的大量工作。该研究项目的主要目标包括：1.测量概念和校准试验台的构建2.根据不同的试样宽度推导校准函数3.开发用于分解膜应力中的法向压力的数学方法4.流量的确定用薄膜方程描述屈服曲线和屈服轨迹