Effect of Plastic Anisotropy on Forming Limit Prediction

A model based on Marciniak-Kuczynski (M-K) theory [1] for the prediction of forming limit diagrams (FLDs) for anisotropic sheet metals is presented. The plastic anisotropy is taken into account by the shape of the yield locus generated on the basis of measured crystallographic texture. As a result, not only the material behavior during the monotonic loading can be well described and predicted, but also the complex strain-path changes during the forming process can be taken into account. Examples of predicted FLDs for two aluminum alloys are given. Comparisons with experimental results are presented.

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The forming limit diagram of sheet metals and effects of strain path changes on formability: a dislocation treatment

Materials Science and Engineering ◽

10.1016/0025-5416(82)90181-1 ◽

1982 ◽

Vol 56 (1) ◽

pp. 47-61 ◽

Cited By ~ 13

Author(s):

Y. Bergström ◽

S. Ölund

Keyword(s):

Strain Path ◽

Forming Limit Diagram ◽

Forming Limit ◽

Sheet Metals ◽

Strain Path Changes

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Orientation and Path Dependence of Formability in the Stress- and the Extended Stress-Based Forming Limit Curves

Journal of Engineering Materials and Technology ◽

10.1115/1.2931152 ◽

2008 ◽

Vol 130 (4) ◽

Cited By ~ 5

Author(s):

C. Hari Manoj Simha ◽

Kaan Inal ◽

Michael J. Worswick

Keyword(s):

Strain Path ◽

Path Dependence ◽

Forming Limit ◽

Stress Space ◽

Forming Limit Diagrams ◽

Metall Trans ◽

Strain Paths ◽

Strain Path Changes ◽

Path Dependent ◽

Forming Limit Curves

This article analyzes the formability data sets for aluminum killed steel (Laukonis, J. V., and Ghosh, A. K., 1978, “Effects of Strain Path Changes on the Formability of Sheet Metals,” Metall. Trans. A., 9, pp. 1849–1856), for Al 2008-T4 (Graf, A., and Hosford, W., 1993, “Effect of Changing Strain Paths on Forming Limit Diagrams of Al 2008-T4,” Metall. Trans. A, 24A, pp. 2503–2512) and for Al 6111-T4 (Graf, A., and Hosford, W., 1994, “The Influence of Strain-Path Changes on Forming Limit Diagrams of Al 6111 T4,” Int. J. Mech. Sci., 36, pp. 897–910). These articles present strain-based forming limit curves (ϵFLCs) for both as-received and prestrained sheets. Using phenomenological yield functions, and assuming isotropic hardening, the ϵFLCs are transformed into principal stress space to obtain stress-based forming limit curves (σFLCs) and the principal stresses are transformed into effective stress and mean stress space to obtain the extended stress-based forming limit curves (XSFLCs). A definition of path dependence for the σFLC and XSFLC is proposed and used to classify the obtained limit curves as path dependent or independent. The path dependence of forming limit stresses is observed for some of the prestrain paths. Based on the results, a novel criterion that, with a knowledge of the forming limit stresses of the as-received material, can be used to predict whether the limit stresses are path dependent or independent for a given prestrain path is proposed. The results also suggest that kinematic hardening and transient hardening effects may explain the path dependence observed in some of the prestrain paths.

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