Structural Optimization of Thin-Walled Tubular Structures using Weighted Multi- Objective Approach

1. Abstract This paper focuses on improvement of the crashworthiness of tubular structures using compliant mechanism approach to intelligently tailor local mechanical properties throughout the structure. The ideal crashworthy performance for energy absorbing tubular structures can be achieved by promoting progressive buckling throughout the length of the tube to occur. Progressive buckling is typically achieved when uniform tubular structures are subjected to an axial impact however in practical applications the tubes have geometric imperfections and are subjected to oblique impacts for which Euler buckling / Global Bending deformation is observed. This design methodology relies on the ability of a compliant mechanism to transfer displacement and/or force from an input to desired output port locations. The suitable output port locations are utilized to enforce desired buckle zones, mitigating the natural Euler-type buckling effect. However compliant mechanism approach increases the compliance of the structures/decrease the stiffness of the structures. This paper uses a weighted linear combination of two objective functions of maximizing the MPE (Mutual Potential Energy) and minimizing the SE (Strain Energy). The objective is to find the distribution of the value of thickness over the entire tubular structure to achieve progressive buckling while improving the energy absorption and limiting the peak force. A nonlinear explicit finite element code LS-DYNA is used to simulate tubular structures under impact loading. Biologically inspired hybrid cellular automaton (HCA) method is used to drive the design process. This paper illustrates the use of this design methodology on representative tubular structures which are typical components of vehicle structures. 2.