Comparison of functionally-graded structures under multiple loading angles

•Crashworthiness of thin-walled structures with functionally graded wall thickness under multiple load cases.•Multiobjective optimization for multiple load cases.•Design of functionally-graded wall thickness for energy absorber subject to oblique loads.

This paper provides a comparative study on the crashworthiness of different functionally-graded thin-wall tubes under multiple loading angles, which include hollow uniform thickness (H-UT), hollow functionally graded thickness (H-FGT), foam-filled uniform thickness (F-UT) and foam-filled functionally graded thickness (F-FGT) configurations. First, finite element analyses of these differently graded circular tubes reveal that the F-FGT tube has the best crashworthiness under multiple loading angles. Second, parametric study on the F-FGT tube indicates that the thickness gradient and variation range significantly influence its crashworthiness. Third, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to optimize the F-FGT tube, in which the optimal thickness variation is sought for maximizing specific energy absorption (SEA) and minimizing initial peak force (IPF) under multiple loading angles. The optimized F-FGT tube exhibits better crashworthiness than other three equivalent tube configurations, indicating that the F-FGT tube can be a potential energy absorber when oblique impact loading is inevitable.