A numerical model to analyse the under-tension-bending-unbending processes. Special analysis for determining the spring-back of TRIP 690 steel sheet

In this work, a numerical model has been developed to determine the stresses and deformations involved in the under-tension-bending-unbending processes of metallic sheet strips. The presented procedure allows us to evaluate the behavior in the die radius of a typical deep-drawing process. The procedure is based on a flexible numerical method that can be adapted to many other processes. Experimental results have been obtained from TRIP 690 + EBT steel sheets under different pure shear deformation states. The forces involved as well as the final deformations, or spring-back, after each forming process analyzed (bending, unbending over-unbending and stretching), were determined by introducing these experimental data into the ad-hoc created numerical method. The results obtained by the proposed model have been compared with finite element simulations (FEM) and contrasted with the experimental results. This allows the proposed procedure to be validated as a general method with more accuracy than FEM as permits the thickness of the sheet to be divided into a great number of points or elements.