Crashworthiness Analysis And Multi-objective Design Of Sandwiched Double-tube Under Multiple Loading Cases

The safety risks caused by impact are gaining more and more focus with the rapid development of transportation,aerospace,and other industries.The growing usage of intelligent electronic components,new energy technologies,and other new technologies have also put forward higher and more multifaceted requirements for safety design.Thin-walled tubes are widely used as energy absorbers.The progressive buckling deformation of tubes under axial compression leads to a large amount of energy absorption and a stable load.Many kinds of sandwich double-tube designs have been proposed as optimizations of the thin-walled tube to improve the energy absorption efficiency and design ability.Moreover,the multiple loading cases and multi-objectives in actual engineering bring a significant necessity to explore the design method for complex application conditions based on the high design ability of the sandwich double-tube structure.The sandwiched double-tube structure commonly consists of concentric inner and outer thin-walled tubes and a core between them.The popular core designs include foam materials and multi-cell structures.The sandwich-double tube design improves space utilization but also increases the complexity,making the design optimization more difficult.For example,the inner tube may cause an increase in the initial peak crush force and reduce the structural protection capacity.The novel lightweight materials used as the core will cause an improvement in manufacturing.The key performance indicators such as energy absorption,crush force stability,and the cost couple with each other,causing difficulty in independent controlling.In addition,the sandwiched double tubes have more components than the empty thin-walled tube.The sandwich core may interfere with the deformation of thin-walled tubes,and the related mechanism has not been researched enough.The uncertainty of the impact direction makes it necessary to consider both axial and oblique compression.The multiple loading cases complicate the deformation mechanisms of the structure and hard the crashworthiness design.The characteristics of foam-filled and multi-cell double tubes are analyzed by simulations and experiments in the study.The deformation mechanisms understanding of different structures under different loading conditions is also deepened.Multi-objective optimization strategies and novel sandwich double-tube structures are presented based on the deformation analysis.As an artificial cellular material,aluminum foam has the characteristics of lightweight,high specific strength,and stable compression deformation.The introduction of aluminum foam as a filler could raise the energy absorption of a thin-walled tube.In this study,an analytical method is proposed to decouple the interactions between components of the foam-filled double tubes.The analysis of foam-filled double square tubes reveals the interaction mechanism and energy dissipation mechanism in different stages of the axial compression process.The interaction effect between the inner and outer square tubes is insignificant,and the initial peak force is not affected by any interaction.A novel strategy is proposed to control the initial peak force by shortening the inner tube to get a foam-filled non-equal-length double-tube structure.The shortening of the inner tube can reduce the initial peak force and keep the platform force.The effect of the length difference between the inner and outer tubes on the peak force is analyzed.The non-equal length design strategy significantly improves the stability and controllability of the axial crushing force of the foam-filled double-tube structure.A novel foam-filled double-tube structure is proposed with a combination of square outer and circular inner tubes,and its axial compression simulation is carried out.Compared with foam-filled double square tubes,the novel design significantly improves the deformation intervention and interaction between the inner and outer tubes.The simulation reveals that the deformation of the circular tube changes from a ring mode to a diamond mode affected by the outer square one in the new structure.And,energy absorption of the new structure also shows a high increase.Keeping the thickness of the inner and outer tubes constant,the nearness of the two tubes can increase their deformation intervention and the interaction effect contribution ratio in the crushing force.Depending on the dimensional analysis and decoupling analysis of the interaction effect,a mean crushing force prediction of the novel structure,fitting well with the experimental result,is provided.A corner-filled design is further proposed based on the novel structure by removing the filler on the four sides.The removal can reduce the cost of aluminum but not the specific energy absorption.The glue effect on the novel structure is also explored experimentally.The glue effect between the foam filler and the tubes increases the interaction effect and energy absorption.Therefore,the design can balance the load-carrying capacity,economy,and lightweight requirements.The crash boxes in a vehicle frontal system are optimized and evaluated numerically and experimentally for their protection capacity.The result shows that the energy absorption characteristics of the crash box are different in the axial compression and the trolley impact.The protection capacity of the crash boxes in the trolley impact is not only decided by its load-carrying capability and initial peak force but also influenced by the deformation sequence and stability of other components in the frontal system.Affected by the joint action with other components,the loading direction on the crash box show instability,causing the tilt of the crash box and instability of the system.It is also found that the length and trigger of the box together determine the system stability of subsequent deformation after the initial buckling stage.The foam-filled double-tubular crash boxes with cutout holes in the outer tube were more stable in the impact than those with edge slots.The optimization design strategy for the foam-filled crash box is improved,considering the protection capability,material cost,and stability in complex-system loading.The trolley impact tests verify the effectiveness of the design.This work can guide the foam-filled crash box design and the crashworthiness design of a frontal system.The global buckling of the thin-walled structure under the oblique loading could reduce its load-carrying capability.The axial and oblique crushing performance of tubes both need to be considered,as the loading direction is uncertain in the actual engineering.A barnacle-bionic multi-cell double-tube structure is proposed,inspired by the adaptability of whale-crowned barnacles in the multiple loading cases of the marine.Taper is added to the outer tube to make this novel structure fit both axial and oblique loading.The compression simulations of the barnacle-bionic structure with different loading angles are conducted.This bionic design can improve the energy absorption efficiency in axial compression and stability under oblique loading.And the mixed deformation mode shown on the barnacle-bionic tube under the obliqueloading can delay the full compaction and increase the energy absorption.The deformation analysis reveals that the barnacle-bionic tubes with different cone angles have different deformation patterns.The prediction of the crushing force of the novel structure during the axial crush process is provided using the simplified super bending element method and considering the effect of the cone angle.The study improves the controllability of the mechanical properties of the new structure.