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

• Applicants: Professor Dr. Heinz-Günter Brokmeier; Professor Dr.-Ing. Heinz Palkowski
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Synthesis and Properties of Functional Materials
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282209677

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.

• DFG Programme: Research Grants