Numerical and Experimental study of texture, residual stresses, and eccentricity evolution in drawn copper tubes

在管生产中，壁厚变化的减小（描述为偏心）导致材料节省，并且因此对于昂贵的材料，允许显著的成本节省。如自己的初步研究（AiF13939N、AiF17263N）所示，在拉伸过程中，偏心率可通过两个方向的调整（增加和减少）重复受到影响。与此同时，残余应力状态也会随着刀具设置而发生变化，残余应力的发展取决于变形类型、显微组织和晶粒取向。为了理解影响偏心率和最终残余应力的过程及其模拟描述，理解晶体学取向的发展是必要的。对于固态成形中织构发展的描述，这里是管材拉拔，关于晶体学取向的演变有不同的理论。已建立的理论是晶体塑性理论，如已知的，其未在任何FEM软件包中实现。因此，研究的一个目标是开发一个合适的子程序与有限元软件相结合。因此，采用有限元法对不同孔型（这里是铜管）的管材拉拔过程进行分析研究是可能的。为此，在模型中采用随机晶体取向，并通过实验确定颗粒尺寸。初始残余应力值被用作模型的输入变量。为了考虑非轴对称材料流（由于偏心），偏心值也将是输入数据。模型验证进行了实验研究。在上述AiF项目中开发了用于拔管的基本模型。然而，该模型已被开发为一个三维对称模型，没有考虑偏心率和残余应力和晶体取向的初始状态。此外，局部织构条件和变化必须考虑，因为它影响残余应力状态。将使用中子辐射（管壁上的中等纹理）、高能同步辐射（管壁上的纹理梯度）和EBSD（基于微的局部纹理）进行纹理测量。这些数据将用作输入值以及验证。最后，（局部）纹理对管材拉伸中的a.m.参数的影响应提供一种更精确描述效果的工具。

In tube production the reduction of wall thickness variations, described as eccentricity, leads to material savings and thus, for expensive materials, allows significant cost savings. The eccentricity can be reproducibly affected by adjustments during the drawing process in both directions, increase and decrease, as shown in own preliminary studies (AiF13939N, AiF17263N). At the same time, the residual stress state changes characteristically as a function of the tool settings.The development of residual stresses depends, inter alia, on the type of deformation, the microstructure and crystallographic grain orientations. To understand the process and simulative description thereof affecting the eccentricity and the final residual stresses the understanding of the crystallographic orientation development is necessary. For a description of texture developments in solid forming, here the tube drawing, there are different theories on the evolution of crystallographic orientations. An established theory is the crystal plasticity theory, which, as known, is not implemented in any FEM software package . Therefore, one object of the studies is the development of an appropriate subroutine to be combined with FEM software. Therewith analytical studies of tube drawing with different pass-lines (copper tubes here) using the FEM will be possible.For this purpose, a random crystal orientation will be implemented in the model with an experimentally determined particle size. The initial residual stress values are used as input variables for the model. To consider the non axisymmetric material flow (due to the eccentricity), the eccentricity values will also be input data. The model validation is performed on experimental investigations. The basic model for tube drawing was developed in the above mentioned AiF project. However, this model has been developed as a 3D symmetric model without taking into account the eccentricity and the initial state of residual stresses and and crystallographic orientations. Furthermore, the local texture condition and change has to be considered as it affects the residual stress state. Texture measurements will be performed using neutron radiation (medium texture on the tube wall), high energy synchrotron radiation (texture gradient over the tube wall) and EBSD (micro based local textures). The data will be used as input values as well as for validation. Finally, the effect of the (local) texture on the a.m. parameters in the tube drawing should present a tool for more precise description of the effects.