Crashworthiness Investigation Of Thin-walled Bionic Hierarchical Self-similar Structures

Recently,the safety accidents occur frequently due to the increasing number of car ownership.The thin-walled structures have been widely applied in various energy absorbers of cars because of their excellent mechanical properties,but the conventional single-walled structures still exist defects and disadvantages of unstable deformation modes and low efficiency in energy absorption,therefore,researches about new absorbers with the characteristic of high energy absorption have become an emergent task.Many biological structures with excellent mechanical properties have emerged by reason of natural evolution for billions of years,therefore,in recent years,the subject of bionics design has become the research focus in different engineering areas.To further increase the energy absorption efficiency of thin-walled structures,this article selected the prototype of spider web with outstanding mechanical performance,and designed novel energy absorbers based on the hierarchical and self-similar characteristics.This article fully investigated on crashworthiness performance of new hierarchical and self-similar structures by experiment test and simulation analysis.All contents of this article are showed as:（1）Based on the prototype of spider web,this article proposed the novel hexagonal hierarchical structures and corresponding derivative hexagonal self-similar vertex-fractal structures.Crashworthiness performance of hierarchical and self-similar fractal structures has been investigated systematically by the methods of experiment and simulation.The results shows that both hierarchical and self-similar fractal arrangements can effectively improve the crashworthiness performance of the hexagonal single-walled structure,and comparing with hierarchical organization,the corresponding self-similar organization shows obvious superiority in energy absorption.In addition,different self-similar fractal arrangements at the positions of vertexes and different parameters have important effect on crashworthiness of the 2^stt self-similar vertex-fractal structure,the study shows that increasing the thickness and side length of sub-hexagon and contributes to improve crashworthiness performance of the structure obviously,but the thickness of primary net structure and arc linking is not favorable to crashworthiness performance of the 2^stt self-similar fractal structure.Afterwards,this article performed multi-objective optimization design for the hexagonal and self-similar vertex-fractal structure by the kriging mode and multi-objective particle swarm optimization,and obtained the optimized self-similar vertex fractal structure with optimal parameters and most energy absorption.（2）A novel self-similar side-fractal organization was proposed,and the result shows that the 4^stt hexagonal self-similar side-fractal structure HSF₄ has obvious superiority in crashworthiness performance after comparing triangle,square and hexagon self-similar side-fractal structures.Further,the hierarchical characteristic of HSF4 was studied,the results shows the fractal structure HSF4-2 has the most excellent crashworthiness performance when hierarchical order is 2^nd.In addition,after investigating on the parameters of HSF₄-2,the results show the thickness and side length of sub-hexagon have important effects on energy absorption and deformation modes of HSF₄-2;and energy absorption capacity of HSF₄-2 will increase at first and then decrease after a certain value when thickness keeps increasing;the energy absorption capacity of HSF₄-2 will increase with the impact velocity increasing;the energy absorption of HSF₄ keeps increasing when the impact angle is less than a certain value,but its crashworthiness performance becomes worse after impact angle is greater than the certain value.Afterwards,this article performed optimization designs under multiple impacting conditions for the self-similar side-fractal structure,and the result shows the optimized structures of HSF4 in different dynamic impacting conditions have more excellent crashworthiness performance than the corresponding primary structure.After the investigations in this article,the hierarchical self-similar bionic design can provide excellent ideas for the anti-collision structures,especially,self-similar fractal organizations can effectively improve the crashworthiness performance of thin-walled structures.