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Prediction of Failure during Sheet Metal Forming

This project is aimed at gaining a fundamental understanding of the mechanics of failure during sheet metal forming processes and at developing methods to predict these failures by the use of finite element simulations. The finite element method (FEM) realizes a possibility of so-called virtual prototyping, in which case the testing of new tool designs is carried out through computer simulations of the pressing operation. In particular, data needed by the constitutive models are obtained from simple tests using small specimens. Failure due to instabilities and fracture can be predicted directly from the analysis.

The aim of the first part of this project was to show that the Forming Limit Diagram (FLD) of a certain sheet metal could be obtained by using explicit FEM simulations of the Erichsen cupping test. In particular, the mesh adaptive FEM using a sheet-thickness-based indicator has been used in order to improve the accuracy of the simulation results. The refined mesh can serve as a visual necking indicator. The investigation carried out in the first part of this project was presented in a Licentiate Thesis.

An approach for FE simulation of the hydromechanical deep drawing process has been investigated. As a reference, the corresponding conventional deep drawing is also simulated using different material models for anisotropic sheet material. Numerically obtained results are compared with experimental results.

The hydro-forming process has been proposed as a promising alternative to conventional, hydrostatic and fluid cell forming processes. However, such a process is not widely applied in current production. The reason for rather limited application of hydro-forming is due to the difficulties in controlling the process parameters. A project has been carried in co-operation with Swedish industries and research institutes in which the advantages and disadvantages of different forming processes in connection with tool design from both numerical and experimental points of view.

We have also developed two new mesh refinement indicators based on the gradient of the effective stresses and effective plastic strains, respectively. A program module for implementing these refinement indicators is developed and coupled with the finite element code LS-DYNA.

Page responsible: Bo Torstenfelt
Last updated: 2008-02-07