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RESEARCH PAPERS

A Unified Finite Element Approach for the Study of Postyielding Deformation Behavior of Formable Sheet Materials

[+] Author and Article Information
Xinjian Duan1

Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton L8S 4L7, Canada

Mukesh Jain

Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton L8S 4L7, Canada

Don. R. Metzger1

Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton L8S 4L7, Canada

David S. Wilkinson

Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton L8S 4L7, Canada

1

Present address: Atomic Energy of Canada Ltd., 2251 Speakman Drive, Mississauga, Ontario L5K 1B2, Canada.

J. Pressure Vessel Technol 129(4), 689-697 (Oct 17, 2006) (9 pages) doi:10.1115/1.2767360 History: Received April 18, 2006; Revised October 17, 2006

Deformation and fracture behavior of several formable automotive aluminum alloys and steels have been assessed experimentally at room temperature through standard uniaxial tension, plane strain tension, and hemispherical dome tests. These materials exhibit the same deformation sequence: normally uniform elongation followed by diffuse necking, then localized necking in the form of crossed intense-shear bands, and finally fracture. The difference among these alloys lies primarily with respect to the point at which damage (i.e., voiding) starts. Damage develops earlier in the steel samples, although in all cases very little damage is observed prior to the onset of shear instability. A unified finite element model has been developed to reproduce this characteristic deformation sequence. Instability is triggered by the introduction of microstructural inhomogeneities rather than through the commonly utilized Gurson-Tvergaard-Needleman damage model. The predicted specimen shape change, shear band characteristics, distribution of strain, and the fracture modes for steels and aluminum alloys are all in good agreement with the experimental observations.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Nonstandard specimen used in the in situ SEM observation. All units in millimeters.

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Figure 2

Specimen used in the strain mapping by the ARAMIS ® for AA6111-T4. All units are in millimeters. The thickness is 0.92mm.

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Figure 3

Illustrated sequence of deformation during tensile test of sheet materials: uniform deformation, diffuse necking (point A), localized necking (point B), and fracture (point D)

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Figure 4

Experimentally observed failure modes for both steel and aluminum alloys

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Figure 5

Comparison of forming limit strains between DP600 and AA5754 sheet

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Figure 6

Measured distribution of the von Mises strain (equivalent plastic strain) from the ARAMIS system for AA6111-T4 at the cross-head displacement of approximately 8.1mm. This is the last image before the fracture.

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Figure 7

FE predicted distribution of equivalent plastic strain (a) and the equivalent plastic strain rate (b) at an applied displacement of 8.01mm

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Figure 8

(a) Comparison of strain profiles at different deformation stages for AA6111 (b) Locations on the load curves where the FEA and the ARAMIS measurements are compared: 6.5mm, 7.0mm, 7.5mm, and 8.0mm

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Figure 9

Comparison between the FE prediction and experimental observations for DQAK steel

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Figure 10

Predicted intense-shear bands with void in the center (a) and the final failure mode (b). The initial notch profile is also plotted in (a). Thickness direction is along the horizontal.

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Figure 11

SEM observations of the crossed shear bands with void nucleated at the interaction and the final failure for AA5754 with double notches at a width of 0.55mm. Thickness direction is along the horizontal. The thickness of the unnotched part is 2.18mm.

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Figure 12

Comparison between the predicted and observed load curves and the failure modes for AA5754. Both images are taken at the end of load-engineering strain curve.

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