A Practical Approach to Consider Forming Effects for Full Vehicle Crash Application

The forming effects along with strain rate, actual material properties and weld effects have been found to be very critical for accurate prediction of crash responses especially the prediction of local deformation. As a result, crash safety engineers started to consider these factors in crash models to improve the accuracy of CAE prediction and reduce prototype testing. The techniques needed to incorporate forming simulation results, including thickness change, residual stresses and strains, in crash models have been studied extensively and are well known in automotive CAE community. However, a challenge constantly faced by crash safety engineers is the availability of forming simulation results, which are usually supplied by groups conducting forming simulations. The forming simulation results can be obtained by either using incremental codes with actual stamping processes or one-step codes with final product information as a simplified approach. Due to the limitation of resource allocated to crash/safety simulations, incremental simulations are usually conducted only on critical parts such as rail components in a utilized vehicle or frame components in a body-on-frame vehicle that are in the major load paths. In this study, the forming process of a front rail simulated by using incremental and one-step codes are studied and incorporated into crash models as an attempt to understand the difference of their influences. By incorporating incremental and one-step forming results, the responses of crash models are compared with those of physical component tests. The forming process of a second frame is simulated by using a different set of incremental and one one-step codes to provide more data points. The forming results are then carried to full vehicle model for frontal impact analysis. The pulses and deformation modes of the full vehicle impact simulation are compared with those of physical full vehicle test. The comparisons are documented in this paper to understand if it is feasible to use the forming results obtained from one-step forming simulation tools in crash models when forming results simulated by incremental forming tools are not available. It was found that differences of crash results do exist when using the two different methods. However in some cases, the results obtained by using one-step forming tool are acceptable especially when the global responses are the main focus of the crash simulations.