Study On Plastic Hinge Mechanical Model And Energy Absorption Theory Of FRP/Metal Hybrid Thin-Walled Structures With Large Deformation

With the increasing requirements for energy saving,emission reduction and environmental pollution reduction,autobody lightweight deisgn has become one of the key areas of automobile design.The use of advanced lightweight materials such as fiber-reinforced plastic(FRP)with high specific strength,specific stiffness,and light-weight is an effective mean to achieve lightweight of autobody.The FRP/metal hybrid thin-walled structures combine metal and fiber-reinforced plastic in a certain proportion and structural form.Through reasonable structure and material design,a stable and controllable deformation mode can be formed,thereby improving the energy absorption capacity of the structure.The FRP/metal hybrid thin-walled structures,which combine the advantages of the low cost,stable deformation,strong toughness of metal materials and the characteristics of lightweight,high specific strength and specific stiffness,and strong designability of FRP,have become the future development trend of advanced multi-material autobodies.At present,some studies and explorations have been carried out on the mechanical response of FRP/metal hybrid thin-walled structures using experimental tests and finite element simulation methods.The cost of designing hybrid thin-walled structures using experimental tests or simulation methods is high.Trial and error is required in parameter design,resulting in the design cycle is long.The theoretical analysis method is to quantitatively express the analytical relationship between the dynamic response and structural parameters such as geometry,material,and loading condition by analyzing the structural deformation and energy absorption mechanism,so as to realize the rapid prediction of the dynamic response of thin-walled structures,find out the improvement direction of the structure and guide the design.Therefore,on the basis of experimental testing and simulation,it is very meaningful and necessary to deeply analyze and summarize the deformation mechanism and energy absorption law of FRP/metal hybrid thin-walled structures,and to establish an analytical theory model of energy absorption.In this work,based on the general project of the National Natural Science Foundation of China(51775228,51875237),a study on mechanical model and energy absorption theory of FRP/metal hybrid plastic hinge and hybrid thin-walled structures with large deformation is conducted.The content includes extracting the FRP/metal hybrid plastic hinge and proposing a theoretical analysis method for plastic hinge mechanical model;analyzing the deformation process of FRP/metal laminates under off-center impact and establishing a dynamic response analytical model;considering the spatial and direction distribution,based on the hybrid plastic hinge mechanical model,the analytical expression of the energy absorption theory of the FRP/metal hybrid square tube is derived;based on the established analytical expression of the energy absorption theory,a variable thickness FRP/metal hybrid square tube is proposed and its axial crushing performance is analyzed.energy characteristics;a fast forward design of car seat and front end structure is achieved through the proposed theoretical model.Firstly,the basic and common characteristics of the FRP/metal hybrid thin-walled structures in the process of large deformation is analyzed Extract the fiber-metal hybrid plastic hinge(hereinafter referred to as hybrid plastic hinge)as the basic energy absorption element of the FRP/metal hybrid thin-walled structures.The relationship between the structural form of the hybrid plastic hinge and the stress distribution is analyzed.The establishment method of the dynamic model of the hybrid plastic hinge is proposed to obtain the mathematical expressions of the bending moment,membrane force and yield criterion.The effect of thickness,stress and other factors on the yield curve is analyzed.The mechanical modeling method of FRP/metal hybrid plastic hinge is summarized.Secondly,taking the FRP/metal laminate as a typical representative of the autobody panel,based on the mechanical modeling method of FRP/metal hybrid plastic hinge,the hybrid plastic hinge with arbitrary number of layers is established considering the uncertainty of the loading position of the FRP/metal.Establishment and simplification method of yield curve is proposed.The motion field distribution of FRP/metal laminate impacted at different positions(off-center impact)is analyzed.Based on the energy conservation equation,the control equation is established and solved,and the theoretical expressions of the maximum transeverse displacement and impact force are obtained.Results show that the theoretical analytical solution using the inscribing square yield curve agrees well with the simulation results.Thirdly,taking the FRP/metal hybrid square tube composed of FRP/metal laminates as a typical representative of the autobody load-bearing parts,the deformation and energy absorption process of FRP/metal hybrid square tube under axial loading is studied based on the mechanical modeling method of FRP/metal hybrid plastic hinge,and the spatial distribution of the hybrid plastic hinge in the super-folding element during the axial collapse deformation of the FRP/metal hybrid square tube is analyzed,and the mathematical expression between mean crushing force and material property,geometric parameter of the FRP/metal hybrid square tube is derived.The energy absorption theoretical model of FRP/metal hybrid square tubes under axial loading is established,and its accuracy is verified by CFRP/Al hybrid square tubes and GFRP/Al hybrid square tubes.Then,based on the established energy absorption theoretical model of FRP/metal hybrid square tubes under axial loading,the variable thickness FRP/metal hybrid square tubes are proposed to improve the axial crushing performance of the tubes.The performance advantages of structures are proved by combining the test and simulation methods.The specific energy absorption,crushing load efficiency and other indicators of the variable thickness FRP/metal hybrid square tubes are analyzed.The results show that the variable thickness FRP/metal hybrid square tubes can effectively improve the axial crushing performance.Finally,taking the conceptual design of the seat frame and the front thin-walled beam structure as an example,the method of applying the FRP/metal hybrid thin-walled structure and its energy absorption theory to the autobody and realizing the rapid design of structural parameters is introduced.The research is conducive to the in-depth understanding of the deformation mechanism and internal energy absorption law of the FRP/metal hybrid thin-walled structures.The proposed energy absorption theoretical model effectively provides the direction to improve performance of the FRP/metal hybrid thin-walled structure.At the conceptual design stage of the hybrid thin-walled structure,the parameters of the energy-absorbing structure are rapidly designed based on the theoretical model.