Combined Hardening Behavior for Sheet Metal and its Application

Abstract

Our major goal in this book is to better simulate the stress strain curves for tension-compression test by proposing a modification of combined hardening behavior, and then predict fracture and optimize the press formability for applications. At macroscopic level, one of the most popular phenomenological models, the combined hardening model has been implemented into ABAQUS/Explicit and a user subroutine (VUMAT) has been developed. This model was used in order to determine whether peculiarities observed in the experimental results can be predicted. The number of material properties to express the hardening is based on easy testing. A simple method to identify the required parameters is introduced. The capability of the proposed hardening model is demonstrated by three case studies: predict ductile fracture and improve press formability of door hinge, study of Incremental forming for complex shape and its improvement, and case study for magnesium alloy sheet to predict ductile fracture of rotational incremental forming. The proposed model shows more accurate results in the prediction of stress strain curves for all kind of material, as well as the stress and strain distribution. For the ductile fracture prediction, door hinge simulation is done by all the three hardening models and given the best way by using combined hardening model; simulation for incremental sheet metal forming of complex shape is combined of both CAM and FEM then implemented and evaluated from the histories of stress and strain value and ductile fracture value (I) by means of finite element analysis, the prediction and optimization of press formability is implemented for negative incremental sheet forming and then investigate by experiment; To simulate the effect of the large amount of heat generation at elements in the contact area due to friction energy of rotational incremental forming for magnesium alloy sheet, Johnson-Cook model was applied and also compared with equivalent stress-strain curves obtained by tensile test at elevated temperatures. The effect of process parameters e. g tool down-step and tool radius on the ductile fracture value and forming limit curve at fracture (FLCF) were investigated using (FE) simulation results.