Study On Energy Absorption Characteristics Of Polyurethane Foam Filled Triaxial Fabric Thin Wall Tube

The superior energy absorption and crashworthiness of composite tubes have attracted the attention of a series of industries.Its light weight,high energy absorption and stable failure process have been widely recognized.Due to its strong designability,it has important applications in the automotive and aerospace fields,and is currently the most potential lightweight material.The triaxial fabric has good in-plane performance,showing quasi-isotropy,the stress distribution is uniform under the action of external force,has strong binding performance in the transverse,the force at the interweaving point shows self-locking characteristics,which makes the triaxial fabric excellent mechanical performance.In this paper,carbon fiber triaxial fabric composite tube was prepared,and polyurethane foam was filled inside to enhance the energy absorption effect.Through quasi-static axial compression experiment,the energy absorption effect of triaxial fabric empty tube was first studied and compared with that of polyurethane filled tube.It was found that foam filling could provide more energy absorption for the triaxial fabric thin-walled tube.The foam-wall interaction can also enhance the energy absorption effect.In this paper,the failure mode and damage morphology of triaxial fabric tubes with different proportions of warp and weft yarns were studied.The weight evaluation was carried out combined with the energy absorption index,and the failure process and damage morphology were analyzed to obtain the role and stress of warp and weft yarns in the axial compression process.The difference between C2C2 and C3C2 is mainly due to the difference in effective compression stroke caused by different warp layers which provide transverse binding force.The difference between C2C4 and C2C2 is due to the different axial loading capacity caused by different filling layers,and the compression curve shows a difference between high and low.The weft yarn has higher participation in compression and can significantly increase the load peak.The existence of warp yarn mainly strengthens the axial bearing capacity of the filling yarn and reduces the buckling damage of the filling yarn.Under the constraint of C2 and C3 layers,the average peak value of filling increases by 45.03% and 98.92% after the same number of filling threads is increased.There are weak jointed regions M and N in the process of compression failure of triaxial fabric pipe.The failure sequence of weak jointed regions will be changed and the failure mode will be affected by the ratio of different warp and weft layers.The weak joint zone of C2C2 and C2C4 appears near the interweaving point of the warp yarn,and the stress concentrates on the warp yarn with small number of layers.The shear failure of the weak joint zone leads to the structural failure.The weak joint area of C3C2 is located near the weft yarn at interweaving point,the axial load is concentrated on the weft yarn,and the brittle fracture of the weft yarn leads to the structural failure.The warp and weft yarns near the C3C4 interweaving point have no obvious weak joint area,and the inner fiber and the outer interweaving point produce more plastic deformation and absorb a lot of energy,and the failure process is stable and has a long effective compression stroke.On the basis of the analysis of the above experimental results,a composite filling tube with plain structure and triaxial fabric is introduced,and its failure process,force mechanism and failure morphology are analyzed.The mathematical model is introduced and supplemented to improve the formula suitable for characterizing the wall-foam strengthening effect of triaxial fabric structure,and the folding evolution process of triaxial fabric is analyzed,and the failure morphology is classified.PW12 is highly dependent on pre-failure.Compared with N-PW12 without pre-failure,the total energy absorption(EA)and load efficiency(CFE)of Y-PW12 with pre-failure increased by 28.77% and 64.19% respectively.The failure morphology of Y-PW12 and N-PW12 with pre-failure presented a "flowering" shape and energy absorption was carried out through scattering failure mode.The shape and size of the fold is affected by the degree of damage.The failure mode of TWF12 is complex,which absorbs energy through buckling failure and brittle fracture.After the plain structure is combined with the triaxial fabric(PW1-TWF2),the bearing capacity of the structure is greatly improved,the failure mode is more stable,and the total energy absorption is increased by 43.46%and 123.07% compared with TWF12 and PW12,respectively.The failure mode changed from a single scattering mode to a mixed failure mode of inner scattering and outer brittle fracture,and the energy absorption effect was significantly improved.Finally,the Hanssen theoretical formula is supplemented.The foam-wall strengthening theoretical model needs to be comprehensively considered in combination with the porosity problem of the triaxial fabric,and the porosity is introduced as the supplementary coefficient.Meanwhile,due to the characteristics of foam filling and pore structure,the folding evolution process of the triaxial fabric pipe is different from the internal and external overturning mode proposed by Wierzbicki.The warp and weft yarns have different movement trends.The warp yarns alternately surround the tube wall,and the wrinkles formed by the weft yarns extend outward to a certain extent and fall off.It is found by optical microscope that the damage degree of the fibers at the interweaving point is different and the weft yarn has the phenomenon of secondary damage shedding.