Investigation of residual stress in a bent Ti-clad Cu bus-bar by neutron diffraction and finite element modelling

Abstract

Titanium-clad copper bus-bars are used to provide corrosion resistance in high temperature electrolytic cells. When cold-formed, such components will have a complex residual stress pattern. We report the investigation of residual stress in a high conductivity Cu bus-bar clad with Grade-2 Ti by neutron diffraction and finite element modelling. Straight bars were co-extruded, air-cooled and cold-stretched. The bars were cold-bent into an inverted ‘top-hat’ shape with four 90° bends. Residual stresses were investigated at the apex of a 90° bend. Three sets of measurements were performed in each of the measurement directions (transverse, normal and axial, relative to the straight bar): one set along the centre line in Cu; one set along the edge in Cu and one set along the edge in Ti. Residual stresses were then calculated in the three directions assuming both materials are elastically isotropic. The cooling, stretching and bending processes were simulated with an explicit finite element program, while the springback was modelled with dynamic relaxation. The neutron diffraction and finite element modelling results show reasonable agreement. Both materials exhibit unbalanced profiles relating to the combination of higher yield stress in the Ti cladding, and larger cross section of the copper bar.