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Research Papers

Numerical and Experimental Investigations of Key Assumptions in Analytical Failure Models for Sheet Metal Forming

[+] Author and Article Information
Brad L. Kinsey

Department of Mechanical Engineering,
University of New Hampshire,
Durham, NH 03824

lCorresponding author.

Manuscript received August 6, 2012; final manuscript received August 22, 2013; published online December 13, 2013. Assoc. Editor: Jyhwen Wang.

J. Manuf. Sci. Eng 136(1), 011013 (Dec 13, 2013) (9 pages) Paper No: MANU-12-1238; doi: 10.1115/1.4025567 History: Received August 06, 2012; Revised August 22, 2013

In this paper, the key assumptions in the M-K and effective stress ratio models are investigated for AISI 1018 steel specimens with a thickness of 0.78 mm using experimental and numerical data from Marciniak tests. The experimental procedure included Digital Imaging Correlation (DIC) to measure the major and minor in-plane strains. Strain components were obtained at points inside (i.e., the defect region) and adjacent (i.e., the safe regions) to the high strain concentrations for four different strain paths. In the numerical analysis, FEA simulations with Marc Mentat were performed with shell elements to investigate the four specimen geometries. The key assumptions of interest are the incremental major strain ratio from M-K model and the critical stress concentration factor from effective stress ratio model. Thus, the mechanics- and material-based failure phenomena in these two analytical models are examined in this paper to provide insight into the material behavior at failure. Also, data are presented that shows clearly the localization (both size and strain value) for the various strain paths.

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References

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Derov, M. J., 2008, “Investigation of a Stress Based Failure Criterion for Sheet Metal,” Master's thesis, University of New Hampshire, Durham, NH.
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Figures

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Fig. 1

Strain-based FLCs for various uniaxial (U), equi-biaxial (E), and plane strain (P) prestrains induced longitudinal (L) and transverse (T) to the major strain direction [4]

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Fig. 2

Representation of main groups of geometries for the Raghavan modification [12]

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Fig. 3

Specimen and washer geometry types [12]

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Fig. 4

Strain paths varying from uniaxial to balanced biaxial cases for the various specimen types

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Fig. 5

AISI 1018 hardening curves

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Fig. 6

Numerical simulated stress paths varying from uniaxial to balanced biaxial cases for the various specimen types

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Fig. 7

Initial strain ratio ρ=dɛ2dɛ1 versus forming depth at failure

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Fig. 8

Contour plots of major true strain for Type II-2 specimens for (a) experimental data [13] and (b) numerical simulation

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Fig. 9

Contour plots of major true strain for Type IV specimens for (a) experimental data [13] and (b) numerical simulation

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Fig. 10

Strain path curves for the defect node and different locations away in the X-direction for Type II-2 specimens for (a) experimental [13] and (b) numerical simulation data

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Fig. 11

Strain path curves for the defect node and different locations away in the X-direction for Type IV specimens for (a) experimental [2] and (b) numerical simulation data

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Fig. 12

Incremental major strain ratios versus forming depth for Type II-2 specimen for experimental [13] and numerical simulation data

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Fig. 13

Incremental major strain ratios versus forming depth for Type IV specimen for experimental [13] and numerical simulation data

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Fig. 14

Initial strain ratio versus incremental major strain ratio directly before failure for experimental [13] and numerical simulation data

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Fig. 15

Critical stress concentration factor (i.e., Fσ¯ parameter) versus the X-direction location for Type II-2 specimens at various distances from failure for (a) experimental [13] and (b) numerical simulation data

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Fig. 16

Critical stress concentration factor (i.e., Fσ¯ parameter) versus the X-direction location for Type IV specimens at various distances from failure for (a) experimental [13] and (b) numerical simulation data

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Fig. 17

Fσ¯ parameter versus distance from the defect node in the X-direction for different specimen types for (a) experimental [13] and (b) numerical simulation data

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Fig. 18

Critical stress concentration factor versus initial strain ratio for both experimental (Exp) [13] and numerical simulation (FEA) data

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Fig. 19

Schematic of Safe (A) And Defect (B) Regions with Varying Thicknesses for M-K Model [5]

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