Study On Energy Absorption Characteristics Of Tubular Composite Structure Filled With Polyurethane Foam Under Lateral Crushing

As an energy absorption element for vehicle collision protection,thin-walled tubular structure can absorb the impact energy in the process of low-speed collision through large plastic deformation,damage and fracture,so as to reduce the damage to occupants and vehicle structure.However,the thin-walled tubular structure has a weak ability to withstand non-axial loads and is prone to Euler buckling,resulting in inadequate energy absorption.In the backgro-und of automotive lightweight design,porous material filling with thin-wall structure provides an important way to solve the contradiction between lightweight and collision resistance in structural design.Rigid polyurethane foam（RPUF）is an excellent porous energy absorbing material.When RPUF is used as a core material to fill thin-walled tubular structure,the bearing capacity and energy absorption characteristics of the structures can be improved.However,the common RPUF material has poor compressive performance and cannot meet the application requirements.In this paper,inorganic particle materials were used as fillers to enhance and modify RPUF,and inorganic particle reinforced RPUF composites were prepared.Using it as the filling core material of carbon fiber reinforced composite material（CFRP）and metal material tubular structure,three types of reinforced RPUF tubular composite structures,namely,foam-filled metal circular tube and foam-filled CFRP circular tube,foam/aluminum honeycomb filled CFRP circular tube and foam/aluminum honeycomb filled CFRP square tube,were prepared.Their mechanical behavior and energy absorption characteristics under lateral crushing were studied,and their compound reinforcement mechanism was further revealed.Specific research contents and results are as follows:Three inorganic particles,hollow glass microspheres（HGMS）,graphene oxide（GO）and nano-silica（Si O₂）,were selected as the basic filling materials.The surface functionalization of HGMS was modified by 4,4’-methylene diisocyanate（MDI）to prepare isocyanate function-alized HGMS material（HGMS-NCO）to enhance the interfacial bonding strength between HGMS and substrate;Through the"molecular bridge"effect of silane coupling agent（KH550）,GO-HGMS cross-linking hybrid materials were prepared to increase the layer spacing of GO and improve the dispersion of GO in polymer matrix materials;Nano-Si O₂particles generated by in situ hydrolysis of tetraethyl silicate（TEOS）were loaded onto the surface of GO through electrostatic adsorption to prepare GO-Si O₂hybrid material and improve the dispersion of GO and nano-Si O₂.Three kinds of inorganic particle fillers were prepared to enhance and modification of RPUF.HGMS-NCO/RPUF,GO-HGMS/RPUF and GO-Si O₂/RPUF composites were prepared,and the effects of the types and contents of reinforcing fillers on the compressive mechanical properties,thermal stability,thermal insulation and waterproof properties of foam composites were studied.The results show that the addition of fillers significantly enhances the compressive mechanical properties and energy absorption properties of the foam composites.GO-HGMS material was the most outstanding in enhancing the compression performance of RPUF,compared with pure RPUF,the compression strength and compression modulus are increased by 146.17%and 199.11%,and the total energy absorption and specific energy absorption are increased by 137.33%and 110.40%,respectively,when the filling content of RPUF is 4 wt%.The lateral crushing performance of GO-HGMS/RPUF-filled metal circular tube and CFRP circular tube composite structure was tested by quasi-static test,and the influences of circular tube structural parameters and foam material properties on the deformation mode and energy absorption characteristics of composite structures were analyzed,the interaction effect between foam filling and circular tube structure was also investigated.The results show that the foam as the core material significantly improves the bearing capacity,bearing stability and energy absorption efficiency of the circular tube structure,and the strengthening effect of the thin-walled tube is better than that of the thick-walled tube;In addition,improving the mechanical properties of foam materials can further increase the energy absorption performance of the structure,compared with pure RPUF filled CFRP thin-walled circular tube（wall thickness is 1 mm）,the total energy absorption and specific energy absorption of GO-HGMS/RPUF（4%）filled structure were increased by 107.95%and 96.62%,respectively.By introducing aluminum honeycomb as the reinforcing phase to prepare the composite structure of foam/aluminum honeycomb,the influence of aluminum honeycomb core and foam material properties on the lateral crushing performance of CFRP circular tube was studied,and the failure mechanism and energy absorption characteristics of the composite structure of CFRP square tube filled with foam/aluminum honeycomb were analyzed.The results show that the inhibition effect of foam material on the deformation of aluminum honeycomb makes the deformation mode of foam/aluminum honeycomb composite structure more stable than that of aluminum honeycomb specimen,and the energy absorption characteristics are more prominent;The improvement of mechanical properties of foam materials further enhances the interaction effect between foam and aluminum honeycomb,and increases the energy absorption capacity of foam/aluminum honeycomb composite structure;Through the above effects,the core material of foam/aluminum honeycomb composite structure improves the stability,bearing capacity and energy absorption performance of CFRP tubular structure.