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C4 - Microstructural Analysis - FEA



Analysis of Load History Dependent Evolution of Damage and Microstructure for the Numerical Design of Sheet-bulk Metal Forming Processes

Project Status: Active

Last Update: 16.03.2020



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The aim of this project is the numerical failure prediction in sheet-bulk forming processes based on coupled damage models, which are motivated and validated by microstructural analysis. This serves the purpose to predict the remaining formability and a safe process window for complex multi-step sheet-bulk forming processes. Hence minor goals are following, like the characterization and modelling of anisotropic hardening, characterization and modelling of strain rate dependencies and the determination of the local loose in stiffness of the workpiece.

Material models developed in the first and second stage to model kinematic hardening, shall be modified to model hardening phenomena like cross-hardening and hardening stagnation, which can be observed for continuous and discontinuous loading path changes in DC04 and DP600. These advanced models are used by TP A4 to adapt process routes of ISBMF in such a manner that locally wanted hardening effects occur. The anisotropic hardening model is combined with a criterion for ductile damage to take into account the impact of load history dependent hardening and evolution of pore structure on fatigue.

The strain rate dependent hardening and fatigue behavior of DC04 and DP600 is to be captured experimentally in a range between 0.001 1/s and 500 1/s. Hence, the developed Gurson- and Lemaitre-based failure models have to be extended with a strain rate dependency to predict the strain rate dependent evolution of damage in the manufacturing as well as the usage. The observed influence of higher strain rates on the evolution of pore structure has to be taken into account for the formulation of the enhanced models.

For a reasonable characterization of initial damage resulting from sheet-bulk metal forming processes and damage due to abrupt dynamic loads in the stage of usage, the resonance method, which was qualified/verified in the second stage, is to be adapted to reduced material volumes, to determine macroscopic damage in predefined areas even for short-term measurements.

 

For the aim of determining above-mentioned cross-hardening effect at large strains, the Bulge-Torsion-Test has been developed at the IUL. The combination of bulge test and torsion test allows an orthogonal strain-path change at plastic strains greater than 0.5. This approach makes it possible to characterize cross-hardening at strains typical for sheet-bulk metal forming.

 

 


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