Study On The Bending Mechanical Behavior And Energy Absorption Characteristics Of Lightweight Thin-Walled Beams

Light-weight thin-walled beams have excellent mechanical properities and energy absorption capacity.They are widely used in transportation devices as energy absorbers to absorb the kinetic energy in accidental impacts and protect the safety of occupations.Transverse bending of thin-walled beams is one of the most important energy dissipation mechanisms.However,the current theoretical studies mainly focus on the pure bending,and they can not reflect and predict the bending mechanical behavior and response of thin-walled beams in the real conditions.This paper aims to investigate the bending mechanical behavior and energy absorption characteristics of thin-walled beams under transverse loading,to provide theoretical methods to analyze the energy dissipation mechanism and predict the response of metallic thin-walled beams,and to offer techanical supports for engineering applications of CFRP(Carbon Fiber Reinforced Plastic: CFRP)reinforced thin-walled beams.The main contents of this paper are as follows:In the first part,three deformation modes: bending collapse,local indentation and bending with indentation modes are defined for thin-walled beams under transverse bending,and a study is carried out to analyze the energy dissipation mechanism of beams developing the bending collapse mode.Experimental and numerical studies are carried to investigate the three-point bending process of rectangular thin-walled beams.The deformation characteristics and load responses(contact force and bending moment in the middle section)of the beams are analyzed.The numerical method is employed to analyze the influence of different geometric parameters on bending collapse of the beams,and the differences between three-point bending and pure bending are investigated.Finally,on the basis of the experimental and numerical results,the Kecman’s model is modified,and a theoretical method is proposed to predict the bending moment response of thin-walled beams deforming in the bending collapse mode.The second part focuses on the local indentation mechanism of thin-walled beams.Experimetal tests are firstly conducted to investigate the deformation and force responses of thin-walled rectangular section tubes under lateral compression.Numerical studies are then performed to simulate the tests,and analyze the influences of geometric parameters on force response.Basing on the deformation features of the tubes,a theoretical model is proposed to analyze the energy dissipation mechanisms for tubes developing local indentation mode.In the theoretical model,the dimesional analysis method is employed to determine the rolling radius of the travelling plastic hinge lines,and the force response of the tubes are derived theoretically.Finally,the experimental and numerical results are employed to validate the theoretical formulas.The third part concentrates on the mechanism of thin-walled beams with bending and notable indentation.Experimental tests and numerical simulations are performed to analyze the bending with indentation deformation process and force responses of the rectangular tubes.The influences of geometric parameters on collapse mechanism are then investigated.Furthermore,basing on the experimental results,a theoretical model is established to analyze the bending with indentation mode.The energy analysis method and dimensional analysis method are employed to derive the theoretical expressions for the force responses of the beams.The fourth part primarily studies the three-point bending collapse and energy absorption characteristics of Al/CFRP multi-cell tubes.Quasi-static and dynamic three-point bending tests are conducted to analyze the deformation mode,force response and energy absorption characteristics of the Al/CFRP tubes.Numerical studies are then performed to simulate the tests and investigate the influences of several critical factors on bending deformation mechanisms and crashworthiness of Al/CFRP tubes.Results show that the deformation modes of Al/CFRP tubes are determined by the relative strength on the resistance of bending collapse and local indentation.Introducing CFRP wrapping can remarkably improve the energy absorption capacity and efficiency of pure Al tubes.The Al wall thickness,partial CFRP wrapping and sectional shape have significant influences on the response of Al/CFRP tubes,while the number of CFRP plies and the initial loading velocity of the punch only have small influences.Partial CFRP wrapping is an effective approach to increase the energy absorption efficiency of the Al/CFRP tubes,and the multi-cell Al/CFRP tubes outperform their single-cell counterparts in crashworthiness.The fifth part focuses on the structural optimization design of Al/CFRP multi-cell tubes to further improve the crashworthiness of the structure.Experimental and numerical studies are conducted to analyze the influence of wrapping angle and ply thickness on the deformation and force responses of Al/CFRP tubes.The sequential response surface method(RSMS)is employed to optimize the structure.Results show that the variation of wrapping angle results in two different failure modes of the CFRP layers.Optimization results indicate that the Al/CFRP tubes with larger wrapping angle and thicker ply thickness achieve higher energy absorption efficiency,and introducing thickness variables in the section can further increase the crashworthiness of Al/CFRP tubes.