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.

The influence of the drawing parameters and temperature rise on the prediction of chevron crack formation in wire drawing

“…However, the obtained results are compared with those available in the literature. Komori (2003), Alberti et al (1993) and McAllen and Phelan (2005) observed a similar effect for the prediction of central bursting defects. Komori (2003) has investigated the occurrence of central burst defects in copper wire drawing using four kinds of ductile fracture criteria (Gurson 1977;Oyane et al 1980;Cockcroft and Latham 1968;Brozzo et al 1972).…”

“…This author has showed that the material at the center of the cross section is fractured in the analysis using Gurson's fracture criterion, Cockcroft and Latham's fracture criterion, Brozzo et al's fracture criterion and Oyane's fracture criterion. Otherwise, Alberti et al (1993) and McAllen and Phelan (2005) have investigated the formation of central burst defects in drawing of UNI-3571 Aluminium alloy and 2011 Aluminium wire respectively. Their results exhibit a curve dividing the safe and unsafe zones corroborating our present findings.…”

“…It was observed that the damage increases with increase in reduction and friction, but decreases with increase in die length. A modified failure model has been developed by McAllen and Phelan (2005) to examine ductile fracture initiation and propagation by central bursting in 2011 Aluminium wire. Results from the numerical model have shown that a nose shape curve divides the safe and unsafe zones for the successful drawing of the wire.…”

Thermomechanical Simulation and Experimental Validation of Wire Drawing Processes

“…The study of this problem has attracted the attention since the end of the 19th century (see [1][2][3] for a historical review on this subject). In recent years, the analysis of this process has encompassed different topics such as: assessment of the influence of drawing variables (e.g., drawing velocity, die geometry and heat treatment) on the material response [2][3][4][5][6][7][8] comparison of finite element simulations with analytical results [7][8][9], estimation of the back tension in single [10], and multistep [11][12][13] processes, surface and internal (i.e., chevron) crack formation [14][15][16][17][18][19][20], experimental and numerical evaluation of residual stresses [21][22][23][24][25][26][27], hydrodynamics in the lubricant layer [28,29], wear prediction [30,31], computation of temperature distribution on the wire [30,32,33], strain rate effects in high-speed forming [34], and texture development [35].…”

Numerical simulation of bursting in extrusion process using finite viscoplasticity with ductile damage and thermal effects

“…Although this type of defect occurs with a small frequency, it is highly insidious because it is usually not visible from the outside and needs special non destructive technique control to be detected. This problem has been addressed in many works using various kinds of local fracture criteria in order to predict the discontinuous chevron shaped cracks formation ( [1][2][3][4][5][6][7][8]). In this paper, thermoelasto-viscoplastic constitutive equations with both non linear isotropic and kinematic hardenings strongly coupled with isotropic ductile damage and thermal effects are used.…”