Reliability Based Designs for Crashworthiness: Decision Under Uncertainty/Uncertainty Modeling

This paper presents a framework to incorporate the notion of reliability into crashworthy designs of automotive vehicle components. Optimal design for crashworthiness is a challenging task in itself as it involves time dependent complex interactions among bodies along with material and geometric nonlinearities. Maximum energy absorption in the structure is widely used as a design criteria in crashworthiness designs as long as penetration levels are kept under allowable limits. These designs behave well and are safe as long as loading conditions and material properties are deterministic however failure can happen due to excessive penetration under uncertain conditions. Hence a semi coupled reliability based crashworthiness design methodology is proposed in which independent reliability assessments are done on the designs at various intermediate levels during an iterative design cycle of a crashworthy structure. Reliability index approach (RIA) is used to incorporate reliability constraint in the design problem where reliability index is evaluated using first order reliability method (FORM). The most probable point of failure (MPP) is determined with respect to the maximum allowable deflection of the structure when loaded. The reliability constraint is satisfied by changing global mass of the structure as the maximum deflection of the structure is dependent on the mass of the structure. Finally a non gradient based method called hybrid cellular automata (HCA) is used to distribute material within the design domain to achieve maximum energy absorption in the structure. The application of the proposed method will be shown with the help of a practical example.