Crashworthiness Design of Vehicle Structures via Equivalent Mechanism Approximations

A new method for crashworthiness optimization of vehicle structures is presented. In the new method, early design exploration is done by the optimization of an equivalent mechanism approximating a vehicle structure. An equivalent mechanism (EM) is a network of rigid bodies connected by prismatic and revolute joints with special nonlinear springs. These springs are tuned to mimic the force-displacement characteristics of thin-walled beams often found in the vehicle body structures. The EM models can be regarded as a super-set of lumped models and thus they are capable of providing better insight to the design issues. Proper selection of the nonlinear spring parameters is essential to successful implementation of the EM models. Identification of the spring parameters involves pre-compilation of databases of the crash characteristics of frequently used structures via LS-DYNA simulations. The pre-compiled databases and EM models are then used in the initial design phase in order to explore the crash deformation patterns and identify the good crash mode (CM). Once the good crash mode is identified, it becomes the target for detailed design stage which uses higher accuracy LS-DYNA models of the vehicle structures. A case study involving design optimization of the mid and lower rails of a vehicle subjected to frontal crash test conditions is presented. The case study demonstrates the effectiveness of the proposed method.