U-Bending Analysis with an Emphasis on Influence of Hardening Models

In this paper the effect of different hardening models in simulating the U-bending process for AA5754-O and DPSteel, taking a benchmark of NUMISHEET'93 2-D draw bending, has been discussed. The simulation of the process is modeled using the finite element code, ABAQUS 6.5. For efficiency, the simulation of the U-bending process is modeled in the finite element program ABAQUSExplicit, while the springback analysis is simulated in ABAQUSStandard as it would take a long time to obtain a quasi-static solution of springback analysis in ABAQUSExplicit. Three hardening models are considered in simulations: isotropic hardening, pure (linear) kinematic hardening and combined (nonlinear kinematic) hardening. The influence of hardening models on predicting springback and final state variables such as equivalent plastic strain, sheet thickness and punch force has been studied. The combined hardening model predicted the springback parameters well and the isotropic hardening overpredicted the springack. The results of springback prediction have been compared with the results reported in the literature. A relation between the level of the final equivalent plastic strain and the amount of springback has been found. Results show that attaining higher amount of the equivalent plastic strain in the sheet leads to less springback after unloading. Comparison between the two materials demonstrates that the aluminum alloy requires lower punch force which means superior formability and exhibits smaller springback.