Study On The Influence Of Roll Forming Effects On Impact Simulation

A number of complex cross-sections and high strength steel products of auto body were produced by roll forming process, which is one of the important technical for automotive lightweight. However, in the roll forming process, the yield and tensile strength of the material are increased, the ductility is decreased, that is named roll forming effect. Due to the roll forming effect, the crashworthiness of the roll forming products will be changed. However, in the conventional automobile crash simulations, the roll forming effect were not considered, which made the simulation results low accuracy. The roll forming effects were imported into the crash model to study the effects of which on the crashworthiness of the auto parts in this thesis.Quasi-static and dynamic tensile tests of high-strength steel were carried out. The tensile tests of the sample which along the rolling direction of0°,45°through90°direction were conducted respectively, the results showed that the anisotropy is not obvious, could be assumed it is an isotropic material. The dynamics of high-strength steel tensile test results show that the strain rate sensitivity coefficient was0.00425. Moreover, four samples tensile test with different stress triaxialities were experimented, the results showed that the fracture strain decreased with the stress triaxiality increasing. Strain rate had less effect on the high-strength steel fracture strain. Johnson-Cook constitutive model was used to characterize the relationship between the flow stress and plastic strain, and Johnson-Cook fracture model was used to characterize the relationship between fracture and stress triaxiality. ABAQUS/Explicit simulation results show that the Johnson-Cook model can characterize the elastic-plastic behavior and fracture behavior of the material well.Different forming effects of the crash simulation were compared, and had the conclusion: the stiffness of the cap-shaped parts increased when the crash models with consider the plastic strain or residual stress. Therefore, the maximum impact force and average impact force significantly greater than the crash model which not considered the roll forming effect. The maximum impact force and the average impact force were smaller than without considering the roll forming effect when consider the thickness variation. The main reason is that the material was thinning when roll forming, which reduce the stiffness of the cap-shaped parts. The energy absorption of the crash models were compared, which show that:energy absorption of cap-shaped parts was most when considered plastic strain; the second was the model when considered residual stress; the energy absorption was at least when consider the thickness variation.