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

在管材生产中，减少壁厚变化(称为偏心)可以节省材料，因此，对于昂贵的材料，可以显著节省成本。正如自己的初步研究(AiF13939N，AiF17263N)所示，在拉伸过程中，偏心可以重复地受到双向调整的影响，即增加和减少。同时，残余应力状态随着刀具设置的变化而发生显著变化。残余应力的发展主要取决于变形类型、显微组织和晶格取向等。要了解影响偏心和最终残余应力的过程及其模拟描述，必须了解晶体取向的发展。为了描述固态成形中织构的发展，这里是管材拉拔，关于晶体取向的演变有不同的理论。一个公认的理论是晶体塑性理论，众所周知，该理论没有在任何有限元软件包中实现。因此，研究的目标之一是开发一个合适的子程序，以便与有限元软件相结合。这样，就有可能用有限元对不同孔型(这里是铜管)的管材拉拔进行分析研究。为此，将在模型中实现随机的晶体取向和实验确定的颗粒尺寸。将初始残余应力值作为模型的输入变量。为了考虑非轴对称物流(由于偏心)，偏心值也将作为输入数据。模型验证是在实验研究的基础上进行的。在上述AIF项目中开发了管材拉拔的基本模型。然而，该模型被发展为3D对称模型，没有考虑残馀应力和晶体取向的偏心和初始状态。此外，由于局部织构状态影响残余应力状态，因此必须考虑局部织构的条件和变化。纹理测量将使用中子辐射(管壁上的中等纹理)、高能同步辐射(管壁上的纹理梯度)和EBSD(基于微观的局部纹理)进行。数据将用作输入值和验证。最后，(局部)纹理对上午的影响。管子图中的参数应该是更精确地描述效果的工具。

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.