Ductile Fracture by Central Bursts in Drawn 2011 Aluminium Wire

Abstract

This paper reports on the application of numerical techniques to predict the initiation and propagation of central burst defects in the wire drawing process. The development and implementation of a suitable failure model into a commercial finite element code, via a user written subroutine, has enabled the occurrence of ductile fracture by central bursting in 2011 Aluminium alloy wire to be successfully analysed. In validating the numerical model, the drawing force, die pressure and occurrence of central burst defects has been compared with previously published experimental data. Results from the numerical model suggest that a ‘nose shape’ curve divides the safe and unsafe zones for the successful drawing of the wire. It follows that no central bursts are expected to occur, regardless of the die angle used, when the reduction ratio is less than a critical value. When central bursts did occur, the effective strain was found to vary periodically along the surface of the wire. These oscillations corresponded with the occurrence of central burst defects and resulted in variations in the final diameter of the wire. These variations in the final diameter of the wire are thought to be representative of an external defect known as ‘bamboo markings’, which are often an external indication of central burst defects within the wire.