Study of Anisotropic Behavior in Tube Drawing Process Using Multiscale Simulation

在精密管材的生产中，即使在工艺的早期阶段，减少偏心也是一个挑战。DFG项目已经表明，可以通过模具倾斜或模具与管之间的偏移量来控制拉拔管中的残余应力。为此，对不同尺寸的铜管进行了检测，并对其偏心程度、残余应力和织构变化进行了实验和模拟分析。建立了三维有限元模型，编制了描述织构变化的UMAT子程序。从文献中提取了晶体塑性(CP)方法描述流动行为所需的弹性和塑性硬化参数，并将其输入到有限元计算中。由于这些参数直接与材料在较低尺度上的结构和性能有关，因此本工作的主要目的是通过多尺度模拟对现有的CP有限元模型进行修正，从而开发基于集成计算材料工程(ICME)概念的模拟模型来评估材料的各向异性行为。然而，现有的模型将首先对铝管进行测试，以检查为其他材料的铜管开发的模型的可行性。将使用多尺度方法来获得最终CPFE模型所需的所有参数。它还将为分析成形过程提供更精确和准确的预测工具，因为在结构层面上的力学性能预测将考虑较小尺度上的特征的影响。此外，利用ICME方法，将建立一个连接四个极端长度尺度(电子-原子-微观-细观)的框架，用于预测管材拉拔过程中的材料行为。它也可以用于其他参数，如不同的材料、不同的压下量和各种倾斜度/偏移值，以及--最后--其他成形工艺。为此，将使用位错动态(DD)模拟来定义硬化规则常数。因此，铜和铝的各向异性硬化参数将通过DD模拟(微尺度)来计算。DD计算的输入将是位错迁移率，这将通过分子动力学(MD)计算(原子)实现。各向异性弹性常数将用改进的嵌入原子法(MEAM)计算，以获得MD计算所需的势。在电子尺度下，用密度泛函理论(DFT)方法得到广义层错能(GSFE)和能量随晶格参数的变化。最后，将用实验测量结果来验证将要开发的框架。

In the production of precision tubes, the reduction of eccentricity is a challenge even at an early stage of the process. The DFG project has shown that it and the residual stresses in drawn tubes can be controlled with tilting of the die or an offset between the die and tube. For this, Cu tubes of various dimensions were examined and their eccentricity, residual stress and texture changes were analyzed experimentally and simulatively. A 3D FEM model was developed and a UMAT subroutine was programmed to describe texture changes. The elastic and plastic hardening parameters required for the Chrystal Plasticity (CP) approach to describe the flow behavior were taken from the literature and imported into the FEM calculations. The simulation results obtained are in good agreement with the experimental data.Since these parameters are directly in conjunction with structure and properties of the material in lower scales, the main aim of this work is modifying the existing CP Finite Element (CPFE) model through multiscale simulation, so developing a simulation model based on the Integrated Computational Materials Engineering (ICME) concept to evaluate the anisotropic behavior of the material. However, the existing model will be first tested for Al tubes to check the feasibility of the model developed for Cu tubes for other materials. The multiscale methodology will be used to achieve all the necessary parameters for the final CPFE model. It will also provide a more precise and accurate predictive tool for analyzing the forming processes because the prediction of mechanical properties in structure level will be performed regarding the effect of features in smaller scales. Moreover, using ICME approach, a framework will be developed that is linking four desperate length scales (electronic-atomic-micro-meso) for the prediction of materials behavior during tube drawing. It should be also possible to be usable for other parameters like different materials, different amounts of reduction, and various tilting/offset values as well as – finally - for other forming processes. For this aim, Dislocation Dynamic (DD) simulations will be used to define the hardening rule constants. Therefore, the anisotropic hardening parameters for both Cu and Al will be calculated by DD simulations (microscale). An input for the DD calculations will be the dislocation mobility, which will be achieved by Molecular Dynamic (MD) calculations (atomic). Anisotropic elastic constants will be calculated by Modified Embedded Atomic Method (MEAM), to be used to achieve the required potentials for the MD calculations as well. At electronic scale, Density Functional Theory (DFT) approach will be used to get the generalized Stacking Fault energy (GSFE) and energy variations as a function of the lattice parameter. Finally, this framework to be developed will be validated with experimentally measured results.