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TECHNICAL PAPERS

Prediction of Ductile Fracture in Metal Blanking

[+] Author and Article Information
A. M. Goijaerts, L. E. Govaert, F. P. T. Baaijens

Materials Technology, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

J. Manuf. Sci. Eng 122(3), 476-483 (Oct 01, 1999) (8 pages) doi:10.1115/1.1285909 History: Received April 01, 1999; Revised October 01, 1999
Copyright © 2000 by ASME
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References

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Stegeman,  Y., Goijaerts,  A., Brokken,  D., Brekelmans,  W., Govaert,  L., and Baaijens,  F., 1999, “An Experimental and Numerical Study of a Planar Blanking Process,” J. Mater. Process. Technol., 87, pp. 266–276.
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Goijaerts, A., Stegeman, Y., Govaert, L., Brokken, D., Brekelmans, W., and Baaijens, F., 1998, “A validated fem model to improve metal blanking,” Simulation of Materials Processing: Theory, Methods and Applications, Twente, pp. 979–984.
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Goijaerts, A. M., Govaert, L. E., and Baaijens, F. P. T., 2000, “Evaluation of Ductile Fracture Models for Different Metals in Blanking,” submitted to J. Mater. Process. Technol.
Goijaerts, A. M., Govaert, L. E., and Baaijens, F. P. T., 2000, “Experimental and Numerical Investigation on the Influence of Process Speed on the Blanking Process,” submitted to J. Manufacturing Science and Engineering Transactions.

Figures

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The blanking process with an indication of the different zones determining the product shape
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Strain hardening behavior
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Experimental results for ductile fracture initiation for varying clearance
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Dimensions of the tensile specimens in mm, thickness is 1 mm
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Minimum thickness of neck after fracture as a function of hydrostatic pressure
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The evaluation of three criteria from literature with one parameter. The critical values C are determined in the 15 percent-experiment; Cockroft & Latham: C=1.40⋅103 [MPa]; Plastic work: C=3.49⋅103 [MPa]; Rice & Tracey, C=2.32[−].
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Results for the adapted Rice & Tracey and Oyane criterion
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Field variable plot of the Oyane integral for an axisymmetric blanking model, at the punch displacement where fracture initiated (15 percent clearance), with two zoomed plots. Maximum value is 2.38. The location of the maximum is in agreement with experimental results.
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Simulation of a tensile test and experimental verification on deformations. In the upper left corner the undeformed tensile specimen is shown with the modelled part(1/8). Upper right, the calculated deformations at fracture initiation are shown with five levels of the equivalent plastic strain. In the center, the three orthogonal views of the deformed specimen are shown with a zoomed plot of the refined mesh in the neck. At the bottom, the experimental fracture surface is compared with the calculated cross-sectional area in the neck at fracture initiation. (Mind the wedge-like shape.)
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The numerical and experimental force displacement curves (left plot). The crosses are the points where the experimental thickness of the neck after fracture is numerically reached for the three different hydrostatic pressures. In the right plot the deformation history of the overall center of the specimen up to the point of fracture initiation (crosses) is presented for the tensile tests under different hydrostatic pressures.
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Validity check in the pressurized tensile tests for the criteria that performed well with a characterization in the blanking process (Table 3). Rice & Tracey and Oyane et al. deviate respectively 60 percent and 30 percent from the 500 MPa experiment, when the C is determined in the experiment at room pressure.
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Validity check of the proposed criterion for the tensile tests
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Validity check of the proposed criterion for the blanking process

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