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TECHNICAL BRIEFS

Prediction of Central Bursting in Drawing and Extrusion of Metals

[+] Author and Article Information
A. R. Ragab

Department of Mechanical Design and Production, Faculty of Engineering,  Cairo University, Giza 12613, Egypta.r.ragab@link.net

S. N. Samy

Department of Industrial Engineering, Faculty of Engineering,  Cairo University—Fayoum Branch, Fayoum, Egypt

Ch. A. Saleh

Department of Mechanical Design and Production, Faculty of Engineering,  Cairo University, Giza 12613, Egypt

J. Manuf. Sci. Eng 127(3), 698-702 (Jun 23, 2004) (5 pages) doi:10.1115/1.1961982 History: Received November 30, 2003; Revised June 23, 2004

In this work central bursting in drawing and extrusion of metals is investigated. The analysis is based on a modified stress distribution within the die zone due to Shield (Shield, R. T., 1955, J. Mech. Phys. Solids, 3, pp. 246–258) together with Gurson–Tvergaard’s yield function (Tvergaard, V., 1981, Int. J. Fract., 17, pp. 389–407) and its associated flow rule for voided solids. The effects of hardening and evolution of void shape on void growth are considered. Various fracture criteria are employed to predict the process conditions at which central bursting occurs. The first criterion is due to Avitzur (Avitzur, B., 1968, ASME J. Eng. Ind., 90, pp. 79–91 and Avitzur, B., and Choi, J. C., 1986, ASME J. Eng. Ind., 108, pp. 317–321), the second and simplest criterion is based on vanishing mean stress while a suggested third criterion depends on the current value of the void volume fraction. Two other criteria which are basically due to Thomason’s internal necking condition (Thomason, P. F., 1990, Ductile Fracture of Metals, Pergamon, Oxford) as well as McClintock’s shear band formation criterion are applied (McClintock, F. A., Kaplan, S. M., and Berg, C. S., 1966, Int. J. Fract. Mech., 2, p. 614, and McClintock, F. A., 1968, in Ductility, ASM, Metals, Park, OH). The critical process conditions are predicted and compared with the available experimental data. Comparison showed that predictions based on the vanishing mean stress and the current void volume fraction criteria are closer to experiments than those based on Thomason’s internal necking and McClintock criteria.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison among predictions of central bursting based on various criteria for rod extrusion (m=0.02, n=0.05, fi=0.01, λ1i=0.25)

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Figure 2

Comparison among the critical void volume fractions and area reductions at central bursting according to various criteria in rod extrusion (fi=0.01, n=0.05, m=0.02, λ1i=0.5, α=30deg)

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Figure 3

Effect of friction on central bursting predictions for rod extrusion (n=0.1, fi=0.01, λ1i=1)

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Figure 4

Comparison among critical initial porosities (oxygen content) at different die angles according to various criteria (n=0.3, m=0.08, λ1i=1.5, 20% reduction per pass). Experimental points are for wire drawing of copper.

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Figure 5

Comparison of predictions of central bursting according to various criteria with experimental results in rod extrusion of iron alloys (m=0.02, n=0.08, fi=0.02, λ1i=0.25)

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Figure 6

Comparison of predictions of central bursting according to various criteria with experimental results in rod extrusion of commercial aluminum (m=0.08, n=0.173, fi=0.02, λ1i=0.25)

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