Combined kinematic/isotropic hardening behavior study for magnesium alloy sheets to predict ductile fracture of rotational incremental forming

Abstract

In order to predict the ductile fracture of rotational incremental forming for magnesium alloy sheet , a combination of kinematic and isotropic hardening law is implemented and ev aluated from the histories of ductile fracture value (I) by means of finite element analysis. Here, the criterion for a ductile fracture, as developed by OYANE, [J. Mech. Work. Tech. 4 (1980), pp. 65-81], is carried out via a user material, using finite el ement code. To simulate the effect of the large amount of heat generation at elements in the contact area due to friction energy of the rotational toolspecimen interface on equivalent stress-strain evolution in incremental forming, Johnson -Cook model was applied and also compared with equivalent stress -strain curves obtained by tensile test at elevated temperatures. The FE simulation results of ductile fracture was then compared with the experimental results of 80 mm × 80 mm × 25 mm square shape with 45°, 60°, and 80 mm × 80 mm × 20 mm square shape with 70° wall angles. The trend of FE simulation results were quite in good agreement with experiment results. Finally, the effect of process parameters e. g tool down -step and tool radius on the ductile fract ure value and forming limit curve at fracture (F LCF) were investigated using FE simulation results

Relevant material characterization for load prediction in incremental forming

“…Results show a strong discrepancy between the predicted forces but the use of the mixed hardening model leads to a relevant decrease (up of 20%) in the FE simulation of a frustum cone with a wall angle of 50°. Such a conclusion is also presented in the case of AA5754-O sheets of thickness 1.5 mm [18], of magnesium alloy AZ31 sheet with a thickness of 1 mm [19], as well as an overestimation of the load with an isotropic hardening model for AA5182 sheets [20]. Henrard et al [21] have also investigated the effect of different mechanical models (yield criterion, hardening type and hardening law) on the force prediction for the same material AA3003-O.…”