Yoshida-Uemori model: Improvement of the elastic modulus evolutive model and Springback application

Today, a combined hardening model coupled with the elastic evolution modulus which depends on the equivalent plastic strain, called Yoshida-Uemori model, is recommended for an improved springback prediction in stamping numerical simulation. The identification of the elastic evolution modulus parameters is based on hysteresis loops realized between 0.2% of plastic deformation and uniform elongation (UEL), by steps of 1%. The direction change point of each loop is close to 5 MPa. At the equilibrium state of a stamped part after springback, the stress state is not zero at all integration points. Two solutions allow to improve the elastic modulus evolutive model to consider the final stress state in addition to the cumulative plastic deformation. The first solution consists at an implement a full loops model in FEA code; The second solution is to realize two springback steps: the first is a step with constant elastic modulus to obtain the final stress state then defined a model according to this stress state and plastic equivalent strain. To demonstrate the benefits of considering the final stress state in addition to the cumulative plastic deformation, the 2nd solution is applied in the springback prediction of U-form stamping part.