| With high specific strength,excellent specific energy absorption rate and specific surface area characteristics,carbon nanotube(CNT)fiber has a wide application prospect in microelectronic devices,aerospace,protection engineering and other fields.However,at present,the research on dynamic mechanical properties of CNT monofilament is insufficient,especially due to the limitation of experimental conditions,the research on dynamic response mechanism of transverse impact is still lacking.In this paper,an experimental device for transverse mechanics of fiber monofilament was designed,and Nylon fiber was compared.On this basis,the deformation and failure mechanism of carbon nanotube fiber under different transverse loading speeds were discussed.Based on the one-dimensional characteristics of fiber materials,the axial failure of CNT fiber is accompanied by local tension when it is subjected to lateral load.Therefore,the axial tension experiment of CNT fiber is carried out by using quasi-static tensile tester.Self-spun CNT fiber(CNTF-1)and commercial CNT fiber(CNTF-2)are used.The results show that the tensile strength of CNTF-2 is lower than that of CNTF-1,and CNTF-1 with high twist angle breaks after large deformation,and the fracture filament drawing phenomenon of CNTF-2 is obvious.Under the condition of higher strain rate loading,the strength of CNTF-2 increases,but the fracture strain decreases.The transverse mechanical properties of fiber are related to its reliability in engineering application.Therefore,an in-situ transverse loading system of fiber monofilament was set up for in-situ experiment,and the tension-cutting process of CNT fiber in transverse cutting was observed.The results showed that CNTF-1 could solve the spiral failure under quasi-static transverse loading.The transverse impact experiment of CNT fiber is carried out by using the fiber monofilament transverse impact experimental device.the results show that Compared with the time-varying process of fiber transverse impact strength,CNTF-1 and CNTF-2 have viscoelastic tensile stage,strengthening tensile stage and impact failure stage,and the viscoelastic tensile stage of CNTF-1 lasts longer than that of CNTF-2.With the increase of transverse impact velocity,the load amplitude and the slope of load time history curve of CNTF-2 have an increasing trend,while the loading time has a decreasing trend.When the fiber is subjected to transverse load,it will be damaged like filament drawing and even fail.With the increase of loading speed,the shape of the damaged section becomes smoother.Based on the experimental results,the evolution law of mechanical quantities such as impulse and peak stress under fiber transverse impact was statistically analyzed,and the relationship between fiber impact fracture angle,density and elastic modulus under different transverse loading speeds was established by using dimensional method.After that,the finite element numerical method is used to simulate the deformation process of fiber at different speeds.The results show that with the increase of impact speed,the impact fracture angle of fiber increases and the growth rate gradually slows down,which is in good agreement with the conclusion predicted by dimensional analysis theory.The dimensional analysis formula of impact fracture angle at medium and low speed is modified by introducing strength characteristics.This study has certain reference significance for the transverse dynamic fracture properties of fibers under low-speed impact,which is conducive to the optimal design of high-performance CNT fibers and promotes their application in engineering field. |
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