Research And Optimization On The Functionally Graded Thin-wall Structure In Crashworthiness

Ecological awareness and economic pressure force automobile manufacturers to decrease the weight of vehicles, consuming of energy sources and the emission. To lighten its weight without reduce its original ability, a new kind of method was supposed recently that making the components of vehicle functionally graded so that the ability could even rise while weight dropped. The energy absorption devices is the key component when a crashing accident happen, which will deform heavily to absorb energy, protecting the passengers’ safety.Functionally graded foam(FGF) and functionally graded wall(FGW) has been recently gaining comprehensive attention due to its excellent energy absorption capacity under axial impact. However, energy absorption devices will rarely experience pure axial loading in real world, but rather oblique loads, especially during an actual vehicle crash event. This paper aimed at investigating the crashworthiness of the functionally graded foam-filled uniform wall(FGF-UW) square tube and the uniform foam-filled functionally graded wall(UF-FGW) circle tube under multiple load case s. The foam density of FGF in FGF-UW square tube varies throughout the axial direction and is controlled by gradient exponent n. Numerical comparative analysis results reveal that the FGF-UW square tube exceed the corresponding uniform foam-filled uniform wall(UF-UW) square tube in crashworthiness under oblique impact loading, and parameter n has a significant effect on crashworthiness of FGF-UW square tube. The thickness of outside wall in UF-FGW circle tube varies throughout the axial direction and is controlled by gradient exponent m. It is revealed by numerical comparative analysis results that the UF-FGW circle tube exceed the corresponding other three kinds of tubes in crashworthiness under oblique impact loading, and parameter m and the range of the thickness has a significant effect on crashworthiness of UF-FGW circle tube.To optimize the crashworthiness of FGF-UW square tube under some specific angles, the Non-dominated Sorting Genetic Algorithm(NSGA-II) is used to seek for an optimal gradient, in which a surrogate modeling method, specifically the RBF method, is adopted to formulate the Specific Energy Absorption(SEA) and Initial Peak Force(IPF) functions. The results found that the optimal designs are different under different impact angles. Therefore, a multiobjective optimization design process including multiple impact angles was implemented to improve the robustness. The results obtained by optimizations further indicate that the FGF-UW square tube compared with the UF-UW square tube has better crashworthiness. Therefore, FGFT is recommended as a potential absorber of crashing energy. After that, similarly using the RBF and NSGA-II to implement multiobjective optimization design process including multiple impact angles, the optimal UF-FGW circle tube is compared with the other three kinds of corresponding circle tubes, indicating that UF-FGW circle tube is a better choice of energy absorption devices with better performance in crashworthiness.