Study On Energy Absorption Characteristics And Crashworthiness Optimization Of Thin-walled Structures

As important energy-absorbing components,thin-walled structures have been widely used in automotive,rail transportation,aerospace and other fields.Thin-walled structures can dissipate a large amount of impact energy through the crushing deformation theirselves in the event of collision,thereby effectively reducing impact load.Studying the energy absorption characteristics of thin-walled structures is of great significance for the crashworthiness of automobiles and other transportation tools.At present,most of researches are carried out on the axial energy absorption of thin-walled structures.The research on the energy absorption characteristics of thin-walled structures under different angle loads is very lacking.In a real vehicle collision,a pure axial impact occurs rarely,and a common situation is that there is a certain angle between the direction of impact load and the axial direction of energy absorbing devices.The thin-walled structures proposed considering axial loads,although having excellent axial energy absorption characteristics,doesn’t necessarily exhibit good crush performance under oblique loading.In the present work,based on numerical simulation technology,experimental verification,theoretical analysis and multi-objective optimization methods,a series of research work is carried out in order to improve the energy absorption characteristics of thin-walled structures under different angle loads.With a deep comprehension of the crushing deformation mode and energy absorption characteristics,three methods for enhancing the crush performance of thin-walled structures under different angle loads are proposed.The main works of the dissertation are as follows:The main research works of this thesis can be summarized as follows:(1)The energy absorption characteristics of foam-filled thin-walled square tubes under different angle loads are studied.Based on the Super Folding Element theory,introducing initiators on the thin-walled tubes is believed to an effective method in order to enhance the crush performance of foam-filled thin-walled structures.The effects of types and number of crush initiators on the crush behavior of foam-filled thin-walled tubes are analyzed.Based on the comprehensive energy absorption characteristics assessment method,the best suitable type and number of initiators are determined.A multi-objective optimization method is used to derive the structural parameters design of foam-filled thin-walled square tubes with the best suitable type and number of initiators.(2)The energy absorption characteristics of multi-cell square tubes under different angle loads are studied.Theoretical expressions for the mean crushing force of multi-cell tubes are derived by applying the Simplified Super Folding Element theory and verified by numerical simulation method.The effects of cell number,wall thickness and initial velocity of impact loads on the crush characteristics of multi-cell tubes are analyzed.Based on the design principle of uniform strength beam,a layered multi-cell tube whose strength gradually changes along the axial direction of tube is proposed to enhance the energy absorption characteristics of multi-cell tubes under different angle loads.The effects of layer number,wall thickness and initial velocity of impact loads on the crushing behavior of layered multi-cell tubes are discussed.Based on the comprehensive energy absorption characteristics assessment method,the layered multi-cell tube with the best crushing performance under different angle loads is determined.The effects of the wall thickness of each tube on the energy absorption characteristics of the optimal layered multi-cell structure are analyzed.The wall thickness of each tube is optimized via the optimization design method to improve further the crushing performance of the layered multi-cell structure under different angle loads.(3)The crushing performances of single and bitubular polygonal tubes under different angle loads are studied.The effects of interaction between inner and outer tubes,side number of polygonal tubes and loading angles on energy absorption characteristics of polygonal tubes are analyzed.Based on the comprehensive energy absorption characteristics assessment method,the bitubular tube with the best crushing performance under different angle loads is determined.In order to improve the energy absorption characteristics of bitubular tubes under different angle loads,a bitubular tube with double functionally graded thickness along the axial direction of tube is proposed.The effects of gradient index and minimum wall thickness of the inner and outer tubes on the crushing behavior of the functionally graded bitubular tube are analyzed.The optimal gradient index and wall thickness of the inner and outer tubes of the functionally graded bitubular tube are determined via the multi-objective optimization method.