Neutron Stress Imaging of Drawn Copper Tube: Comparison with Finite-Element Model

Seamless tubes are used for various mechanical applications, often produced by several cold drawing steps to reach the required dimensions. The first process step, for example, extrusion or rolling, typically results in ovality and eccentricity of the tube caused by nonsymmetric material flow and being present during the cold drawing process, i.e., no homogeneous deformation. Because of this nonsymmetrical deformation, and deviations over the length of the tube caused by moving tools, this process step generates inhomogeneous residual stresses. To understand the interconnection between geometrical changes in the tubes and the resulting residual stresses, the residual strain distribution in a copper tube was measured by neutron diffraction. The aim of this study is to evaluate residual stresses generated during cold drawing of copper tubes. This research comprises experimental measurements and numerical analysis. An industrially produced copper tube was cold drawn, and the profile of residual strain over circumference and across wall thickness was measured by neutron diffraction. In parallel, a three-dimensional finite-element model (FEM) was developed to calculate the residual macrostress state generated by the forming process. Good agreement between experimental results and numerical computations was obtained.