Testing and Finite Element Modeling of Hydroform Frames in Crash Applications

Hydroformed components are replacing stamped parts in automotive frames and front end and roof structures to improve the crash performance of vehicles. Due to the increasing application of hydroformed components, a better understanding of the crash behavior of these parts is necessary to improve the correlation between full-vehicle crash tests and FEM analysis. Accurately predicting the performance of hydroformed components will reduce the amount of physical crash testing necessary to develop the new components and new vehicles as well as reduce cycle time. Virgin material properties are commonly used in FEM analysis of hydroformed components, which leads to erroneous prediction of the full-vehicle crash response. Changes in gauge and material properties during the hydroforming process are intuitive and can be reasonably predicted by using forming simulations. The effects of the forming process have been investigated in the FEA models that are created for crash analyses. However, some studies have shown that forming effects alone do little to improve the accuracy of the FEA model. This study incorporates physical material properties obtained from forming simulations with strain rate data to more accurately predict the performance of hydroformed components. In order to verify the accuracy and robustness of the developed modeling methodology, two different frame rails are studied. The validation includes the calibration of simulation results with test data in coupon and component levels. To understand the effects of work-hardening, gauge thinning, and strain rate, a sensitivity study is conducted by using finite element simulations. The effect of each factor on the load deflection relationship, crush distance and deformation mode is discussed. Finally, to verify the modeling methodology, full vehicle simulations conducted prior to physical tests are compared with the results obtained from full vehicle tests. Both the deformation modes and responses of the hydroformed components, frame, and body are discussed.