Development of Validated Generic Road Vehicles for Crashworthiness Through Optimization Procedures

Abstract

The development of passive safety devices for vehicles or setup of virtual tests requires that detailed numerical models are available. Generally, the vehicle manufacturers are unable to release the detailed data for their models due to commercial and legal restrictions. Since finite element models for road vehicles suitable for crashworthiness analysis are very detailed, their complexity involve computations that require long time to perform analysis involving large deformations with plasticity and contact. With the actual computer technology the computational time for these models is measured in terms of days. However, during the design of a new vehicle, the redesign of a component or of a particular safety device, many simulations must be performed to appraise different design solutions. An alternative approach to the use of detailed FEM models is important to reduce calculations time. Multibody models of road vehicles are shown here to be suited for early design phases of such vehicles, components or devices, being the computational time required for any specific crash analysis being measured in same number of minutes than the hours required for FEM models. This work presents a methodology for modeling generic road vehicle models for multibody dynamic analysis that have all the characteristics of a real cars, have crash responses for front and side impact similar to the top of line vehicle of its class for the Euro NCAP test but still are not the exact model of any existing vehicle. The multibody modeling work is based on a previously existing finite elements model of the vehicle. First a strategy to convert the finite element to a multibody system model is presented so that the structural features of the MB model are correlated with those of the complex of the FEM model. The responses of the two models are correlated through selected responses extracted from results of impact simulations regarding occupant safety and energy absorption. The crash scenarios used, according to standards for crash tests, are the same for finite element and multibody models. Selected responses, obtained from the results of the simulations in representative points of the car and the barrier, are used to compare the performance of the models in terms of displacements, velocities and accelerations. The plastic hinge characteristics of the multibody model are redefined, using an optimization procedure to ensure that the selected responses of the multibody and finite element models are similar, thus leading to validated multibody models.