A new approach for the prediction of central burst defects in extrusion and wire drawing is proposed. Central burst defects are troublesome in industry as it is impossible to detect these defects by simple visual examination alone. It is therefore important to identify the combination of process parameters that will reduce the probability of these defects occurring. The proposed approach is capable of accurately predicting when and where a central burst is likely to occur. The influence of die geometry on damage development and subsequent central burst formation is examined using the modelling capabilities of Abaqus finite element software. The ductile fracture criteria of Cockcroft and Latham, Oyane and Chaouadi were employed using a Fortran subroutine, and their ability to predict the onset and evolution of the central burst defect was examined. For relatively lower area reductions and die angles the considered criteria are capable of accurately predicting the morphology of the defect. Under these conditions, the proposed approach shows good agreement with experimental results, confirming its effectiveness and suitability for industrial application. The failure criteria are inadequate in predicting central burst defect formation during conditions of large reduction in area and large semi-die angles. Further development of ductile failure criteria is necessary to accurately simulate defect evolution for all die angles and area reductions.

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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.

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