Study On Wrinkling Resistance Of Automobile Thin Steel Sheet Based On Yoshida Buckling Test

According to the need for lightening of cars, high strength steel has been extensively used to reduce vehicle body weight and improve automobile safety. But the high strength steel parts have more serious wrinkling and local buckling problems in the cold forming process. The wrinkling problem of high strength steel has attracted world wide attention.For a long time, sheet wrinkling numerical simulation is a difficult problem which contains strong nonlinear geometric, material and boundary condition. Even though there are many simulations and experiments researches on sheet wrinkling resistance, the most respective of which is the Yoshida Buckling Test, they are not accurate enough because the real contact situations between sheet and die in stamping progress are ignored.In this thesis, the wrinkling phenomenon of high strength steel-BIF340 and DP600 has been studied combining experiment and simulation method based on Yoshida Buckling Test model, especially the wrinkling after contact removal by considering the sheet’s practical contact situation. The main content of this thesis is as follows:1. The wrinkling mechanism, wrinkling criteria, wrinkling prediction theory have been illustrated. The implementation of wrinkling analytical criterion to FEM software is also introduced, which can be used to predict surface distortion more accurately.2. The standard Yoshida Buckling Test experiments of BIF340 and DP600 have been carried out. The results are compared with FEM results, which show a difference of about 15% between experimental and FEM results. The correctness of the FEM model as well as the prediction accuracy on wrinkling problems is validated.3. Considering the sheet’s practical contact situation, single-contact-interface Yoshida Buckling Test model have been built. The influence of the contact and removing contact on sheet wrinkling height is analyzed. It shows that the wrinkling height is reduced obviously due to the contact, but after released from the contact, the wrinkling height will become larger due to springback. Friction coefficient and contact area, these two parameter’s influence on wrinkling and springback is also studied.4. Four material parameters have been selected to study their sensitivity on wrinkling resistance by uniform experiment design method. And the sensitivity analysis of these four parameters has been carried out from two aspects-one single parameter floating and muti-parameters interaction. Results shows the thickness (t) have the most impact on wrinkling resistance, following are n value, k value and E value.