| Polyurea elastomer is a highly elastic material with excellent protective properties.The composite structure made by compounding it with a variety of metal materials such as aluminium,steel and non-metallic materials such as concrete,has a greater effect on the performance of the substrate in resisting explosions and collisions and impacts.However,less research has been carried out on the application of polyurea in the field of traffic safety and protection,and even less on its application in combination with tubular metal structures to make energy-absorbing cushioning devices to resist impact.This paper used a combination of experimental studies and finite element software simulations to first investigate the physical and mechanical properties and thermal properties of Qtech T190 polyurea(hereafter QT190),Qtech T413 polyurea(hereafter QT413)and Qtech T501 polyurea(hereafter QT501).On this basis,polyurea was sprayed onto the outer surface of the hollow thin-walled aluminium tubular structure(hereafter pure aluminium tubular structure)according to the experimental design to make a coated polyurea-aluminium tubular composite structure(hereinafter coated structure),and the interior of the tubular body was filled with polyurea pouring to make a cast polyurea-aluminium tubular composite structure(hereafter cast structure),and the impact resistance of the composite structure was investigated by conducting falling ball impact test.ABAQUS finite element simulation software was used to simulate and analyse the dynamic response of the polyurea-aluminium tube composite structure under different composite methods when subjected to impact loading.The effect of polyurea and castings on the impact resistance of the pipe body was investigated,and the best ratio of polyurea composite coating for energy absorption and cushioning was derived,as well as the best composite method for simultaneous polyurea casting and coating of the pipe body.The following conclusions have been drawn from the above study.Firstly,the basic performance of the material shows that the density of QT190,QT413and QT501 are 1.1468 g/cm~3,0.9016 g/cm~3and 0.9496 g/cm~3respectively,which will not affect the weight of the composite structure in practical application.QT190 and QT413 have short curing time,simple construction process,and the adhesion between them and aluminium is strong.QT190 and QT413 have a short curing time,simple construction process and strong adhesion between both and aluminium,making them suitable for use as an external coating material for aluminium tube substrates.QT501 has a long curing time and good viscoelastic properties,making it suitable for casting inside the structure.The results of thermal performance studies show that QT190,QT413 and QT501 all have good thermal stability performance with initial degradation temperatures of 261°C,251°C and 253°C respectively,and all have a thermal degradation peak near 400°C with peaks of 1.2%/°C,0.93%/°C and1.13%/°C respectively.All three polyureas had two distinct stages of thermal decomposition,each with approximately the same temperature region,and all can maintain their good material properties and meet service conditions in operating environments below 250°C.Secondly,a study of the impact resistance of the coated structures showed that the maximum deformation values for each coated structure were in the range of 25.32mm～32.33mm and the peak strain was in the range of-9038.2～-10509.45.The pure aluminium tube structure had a deformation value of 78.12mm and a strain value well above the range.Under the condition that the total thickness of the coating was 1mm,the impact resistance of1mm QT190 coating was better than that of 1mm QT413 coating.While the impact resistance of the alternately coated composite coating was better than that of the single coating,and the coated composite structure with the external alternate coating of 0.5mm QT413 and 0.5mm QT190 composite coating successively had the smallest deformation value and strain peak,and was the best among the coated structures.The impact protection effect was the best among the coated structures.A study of the impact resistance of cast structures showed that the maximum deformation values for each cast structure were in the range of 5.82mm～17.54mm and the peak strain values were in the range of-3592.74～-7410.15.Among the composite structures,the cast structure with a dense internal QT501 and an external alternate coating of 0.5mm QT413 and 0.5mm QT190 had the smallest deformation and peak strain values of 5.82mm and-3592.74 respectively,with the strongest impact resistance.The energy absorption efficiency of the polyurea composite protective coating was higher in the case of equal structural mass.In the case of equal structural volume,the impact resistance of the coated composite structure was substantially improved compared to the pure aluminium tube structure,but the effect was weaker than that of the cast composite structure,and the energy absorption cushioning effect of the QT501 polyurea castings was more significant than that of the polyurea coating.At last,the simulation results of the ABAQUS finite element software showed that the model and algorithm used in the calculation process can effectively simulate the damage form and deformation of the polyurea-aluminium tube composite structure in the falling ball experiment.Among the coated structures,the best impact resistance and the smallest deformation was achieved with a value of 27.86 mm for the coated structure with alternating external coatings of 0.5 mm QT413 and 0.5 mm QT190.Among the cast structures,the one with a dense QT501 cast inside and a 0.5mm QT413 and 0.5mm QT190 composite coating applied alternately on the outside had the smallest deformation,with a value of 6.341mm,and was the best impact resistant cast composite structure.The pure aluminium tube structure has the largest deformation value of 70.52mm and the worst impact resistance.The data obtained from the simulations were in good agreement with the results of the falling ball impact tests,and the error was controlled in the range of 1.09%～10.03%,and the variation pattern shown in the displacement cloud was more consistent with the falling ball impact tests.In conclusion,QT190,QT413 and QT501 polyureas have good mechanical properties,and when they are combined with the pipe substrate structure in a reasonable way,the impact resistance is significant and has practical engineering significance and good application prospects,providing a certain experimental basis for the application of polyureas in the field of impact absorbing cushioning. |
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