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Research Papers

An Experimental and Numerical Assessment of Sheet-Bulk Formability of Mild Steel DC04

[+] Author and Article Information
Celal Soyarslan1

 Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyCelal.Soyarslan@iul.tu-dortmund.de

Dennis P. F. Fassmann

 Institut für Werkstoffkunde, Leibniz Universität Hannover, 30823 Garbsen, Germanyfassmann@iw.uni-hannover.de

Björn Plugge

 Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyBjoern.Plugge@iul.tu-dortmund.de

Kerim Isik

 Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyKerim.Isik@iul.tu-dortmund.de

Lukas Kwiatkowski

 Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyLukas.Kwiatkowski@iul.tu-dortmund.de

Mirko Schaper

 Institut für Werkstoffkunde Leibniz Universität Hannover 30823 Garbsen, Germanyschaper@iw.uni-hannover.de

Alexander Brosius

Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyAlexander.Brosius@iul.tu-dortmund.de

A. Erman Tekkaya

Institut für Umformtechnik und Leichtbau, Technische Universität Dortmund, 44227 Dortmund, GermanyErman.Tekkaya@iul.tu-dortmund.de

Gurson’s original porous plasticity does not give account for porosity evolution under shear stresses, i.e., zero triaxiality ratio. Reference [7] modifies this formulation where phenomenological softening effects with void distortion and void interaction with material rotation are taken into account.

For q1  = q3  = 0, the porous structure is lost, i.e., the pressure dependence is precluded and conventional isochoric isotropic plasticity is recovered.

In numerical solutions with classical continuum elements, since a length scale is not explicitly involved, element size acts as a length scale.

1

Corresponding author.

J. Manuf. Sci. Eng 133(6), 061008 (Dec 01, 2011) (9 pages) doi:10.1115/1.4004852 History: Received April 01, 2011; Revised July 26, 2011; Published December 01, 2011; Online December 01, 2011

This paper presents investigations on development of a new way of teeth-forming, which is related to sheet-bulk metal forming, with application of incremental bulk forming process to sheets. For this purpose, a combined experimental-numerical study on damage assessment in sheet-bulk forming of DC04 is presented. Using scanning electron microscope (SEM) and glow discharge optical emission spectrometry (GDOS), a combined quantitative/qualitative metallurgical survey is carried out on undeformed specimens to illuminate microstructural aspects in the context of nonmetallic inclusion content, distribution and size which act as prime failure factors. These surveys are extended to monitor ductile damage accumulation with cavitation at different stages of the incremental sheet indentation process over certain sections. An anticipated failure mode is captured where formability is limited by severe macro-cracking preceded by localization with void sheeting. To this end, using a developed VUMAT subroutine for the micromechanically based Gurson damage model which is recently enhanced for shear fracture, the processes are simulated in ABAQUS/Explicit and comparisons with experiments are provided. The results support the requirement of integrating powerful coupled accumulative damage models in the virtual process design procedure for sheet-bulk metal forming. This requirement also arises from distinct features of these class of processes from conventional sheet metal forming processes which preclude use of forming limit curves.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental setup and regarding dimensions (in mm)

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Figure 2

Superficially detectable damage occurrence and macrocracks

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Figure 3

The structure in the lower part of the image shows the damaged edge region of the tooth flank (point a). In addition to individual voids, signs of strong material movement can be observed.

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Figure 4

Fracture surface of the material in the area of the tooth root (Fig. 3 point b)

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Figure 5

Positioning of the examination zone in the geometry

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Figure 6

Less severe cracking at parallel orientation of rolling and forming direction

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Figure 7

Severe cracking behind the heavily damaged cutting edge

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Figure 8

Void nucleation and growth in the bulk material

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Figure 9

Deformation and crack patterns for (a) kw  = 0, (b) kw  = 1, and (c) kw  = 2 (the indentation depths differ from 1 mm to 4 mm from left to right)

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Figure 10

Void volume fraction distributions at the indentation zone at the incipient cracking for (a) fhydg, (b) fshrg, (c) fn , and (d) f (kw  = 0, the indentation depth corresponds to 2.86 mm)

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Figure 11

Void volume fraction distributions at the indentation zone at the incipient cracking for (a) fhydg, (b) fshrg, (c) fn , and (d) f, (kw  = 2, the indentation depth corresponds to 1.80 mm)

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Figure 12

Contour plots for (a) triaxiality ratio and (b) w, at the indentation zone at the incipient cracking (kw  = 2, the indentation depth corresponds to 1.80 mm)

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Figure 13

Void volume fraction distributions for (a) fhydg, (b) fshrg, (c) fn , and (d) f (kw  = 2, the model with side-walls, the indentation depth corresponds to 4 mm)

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Figure 14

Contour plots for (a) triaxiality ratio and (b) w (kw  = 2, the model with side-walls, the indentation depth corresponds to 4 mm)

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Figure 15

The contours representing in plane boundaries of the deformed blanks modeled with (the indentation depth corresponds to 1.80 mm) and without (the indentation depth corresponds to 4 mm) side-walls

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Figure 16

Tool force-displacement curves of experiments and simulations

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