Improved Flow Curve Modelling for Bending Processes in the Range of Low Plastic Strains

改进的低塑性应变范围内弯曲工艺的流动曲线建模

• 批准号: 530544475
• 负责人: Professor Dr.-Ing. Gerhard Hirt
• 金额: --
• 依托单位: Institut für Bildsame Formgebung (IBF)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/530544475?language=en
• 关键词: Improved; Flow; Curve; Modelling; Bending

The use of high-strength alloys is common practice in the manufacture of sheet metal parts. Due to high ratios of yield strength to Young's modulus, strong springback effects are to be expected, which influence geometric accuracy and thus represent a significant challenge. The extent of springback depends on the material properties of the material used. The now standard use of numerical simulations to model forming processes requires careful determination of the material data in order to ensure realistic material modelling and thus good prediction quality. It has been shown that the use of constitutive models for flow curve approximation can lead to losses in accuracy, particularly in the initial range, i.e. in the transition range from elastic to plastic material behaviour. This can particularly affect processes that only lead to small strains of the material, as is the case for example in levelling or various bending operations. Previous work has also shown the nonlinear character of elastic unloading and reloading, which cannot be fully represented by classical linear-elastic-plastic models. Furthermore, a decrease of the effective Young's modulus can be observed, which leads to an improved springback prediction when taken into account in the FE model and is therefore already widely used in the simulation of sheet metal forming processes. Finally, the results obtained so far show that, in addition to the description of elasticity, the plastic deformation behaviour also exerts an influence on springback; here, both yield point and the flow curve are decisive. Individual influencing factors and their impact on springback prediction have already been extensively investigated. However, a comprehensive investigation of all relevant effects (elastic behaviour, flow curve, yield point) and their mutual interaction has not yet been carried out after reviewing the state of the art. The overall objective of the project is to improve flow curve modelling for forming processes in which low strains occur. The three-point bending test serves as an example process in order to be able to evaluate the effect of occurring accuracy losses in the flow curve approximation in the area of low strains and the influence of the nonlinear transition area including the variable modulus of elasticity on the springback. For this purpose, first a comprehensive characterization of the selected materials will be carried out in order to subsequently investigate the various influencing factors and their mutual interaction by means of FEM. In addition, a new constitutive model combined with a validated and practicable procedure is to be developed which makes it possible to minimize errors that occur and to increase the prediction accuracy.

使用高强度合金是制造钣金件的常见做法。由于屈服强度与杨氏模量的高比率，预计会产生强烈的回弹效应，这会影响几何精度，因此是一个重大挑战。回弹的程度取决于所用材料的材料特性。现在标准使用数值模拟来模拟成形过程需要仔细确定材料数据，以确保真实的材料建模，从而确保良好的预测质量。已经表明，使用本构模型进行流动曲线近似可能导致精度损失，特别是在初始范围内，即在从弹性到塑性材料行为的过渡范围内。这可能特别影响仅导致材料的小应变的过程，例如在整平或各种弯曲操作中的情况。以往的工作也表明，弹性卸载和再加载的非线性特性，这不能完全代表经典的线弹塑性模型。此外，可以观察到的有效杨氏模量的减少，这导致一个改进的回弹预测时，考虑到在有限元模型，因此已经被广泛用于金属板成形过程的模拟。最后，迄今为止获得的结果表明，除了弹性的描述，塑性变形行为也对回弹产生影响;在这里，屈服点和流动曲线都是决定性的。单个影响因素及其对回弹预测的影响已经得到了广泛的研究。然而，在回顾了最新技术水平后，尚未对所有相关效应（弹性行为、流动曲线、屈服点）及其相互作用进行全面调查。该项目的总体目标是改进低应变成形过程的流动曲线建模。三点弯曲试验作为一个示例过程，以便能够评估在低应变区域中流动曲线近似中出现的精度损失的影响以及包括可变弹性模量的非线性过渡区域对回弹的影响。为此，首先将对所选材料进行全面表征，以便随后通过FEM研究各种影响因素及其相互作用。此外，一个新的本构模型相结合的验证和可行的程序是要开发，这使得它有可能尽量减少发生的错误，并提高预测精度。