Residual stresses evolution in Cu tubes, cold drawn with tilted dies – Neutron diffraction measurements and finite element simulation

• Tube drawing with a tilted die is a method to control the eccentricity as well as the residual stresses in the tube.
• The evolution of residual stresses in copper tubes during drawing with a tilted die was investigated.
• The residual stresses were measured using neutron diffraction method using SALSA@ILL, which has a high beam resolution.
• An interrupted drawing of a copper tube with a tilted die, was performed.
• Three different zones were existed in this tube: the as-received, the deformation zone, and finally the drawn tube.
• A non-symmetric FEM model was developed and verified using the experimentally investigated residual stresses.
• This model simulates the residual stresses for different tilting angles.

The use of cold drawing processes for tubes is a flexible and well-established technology to reduce tube dimensions and improve their surface quality. However, wall thickness deviations over the circumference in the semi-finished goods – eccentricity – and residual stresses can be disadvantageous. Nevertheless, drawing with die tilting is clearly affecting the eccentricity as well as the residual stress development. In this paper the evolution of residual stresses over the wall thickness in cold drawn copper tubes was measured from the as-received state over the condition in the deformation zone with tilted dies and finally to the drawn tubes by means of neutron diffraction analysis at SALSA facility in Institut Laue-Langevin (ILL), Grenoble. A model was developed and the behavior of the residual stresses was simulated using the finite element method (FEM). The information about the evolution was necessary for the model and its verification. With this model – which is taking into account the influence of eccentricity on the residual stress development – the cost intensive neutron diffraction measurements can be reduced strongly. The verified model was used to calculate the residual stresses for standard drawn tubes and compared to tilted ones.

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