| The main objective of this dissertation is to generate cyclic stress-strain curves for sheet metals so that the springback can be simulated accurately. Material parameters are identified by an inverse method within a selected constitutive model (Chaboche model) that represents the hardening behavior of materials subjected to a cyclic loading.; Three-point bending tests are conducted on sheet steels (mild steel and high strength steel) and sheet aluminum. Punch stroke, punch load, bending strain and bending angle are measured directly during the tests. Bending moments are then computed from these measured data. Bending moments are also calculated based on a constitutive model. Normal anisotropy and nonlinear isotropic/kinematic hardening are considered. Material parameters are identified by minimizing the normalized error between two bending moments. Micro genetic algorithm is used in the optimization procedure. Stress-strain curves are generated with the material parameters found in this way, which can be used with other plastic models.; This dissertation contributes to the generation of cyclic stress-strain curves of sheet metals for more accurate simulation of forming process and especially for springback prediction when the process includes a cyclic loading. |
