Identification of strainrate dependent hardening sensitivity of metallic sheets under in-plane biaxial loading

Wei Liu (INSA Rennes)

CHALLENGE - Sheet metal forming processes are widely used in the manufacturing industry. In many sheet metal working operations, large strains and intermediate strain rates can be reached under biaxial strain or stress states. The objective of this work is to show the potential of the biaxial in-plane tensile test to characterize the hardening behaviour of metal sheets up to large strain levels. 

SOLUTION - Tests have been performed on a dedicated servo-hydraulic machine. These biaxial tensile tests have been carried out on aluminium alloy AA5086 to validate the identification methodology of hardening behavior under biaxial loading.  Digital Image Correlation (DIC) technique is used for strain measurement. The parameters of isotropic hardening models are identified by inverse analysis based on the finite element model of the biaxial tensile test. By numerical investigation, an optimal cruciform shape is designed to obtain large equivalent plastic strain, up to 30%, at the central zone under equi-biaxial strain path. As expected, the initial cracks of tested specimens are always observed at the central zone. The inverse analysis and the optimization process has been performed in modeFRONTIER









BENEFITS - Inverse analysis based on FE model has been applied for parameter identification of hardening laws with strain rate sensitivity. By comparison of uniaxial and biaxial flow stress curves at certain strain rates, it is more beneficial of biaxial tensile tests to identify strain rate dependent hardening behavior up to large strains.