The Research On Interfacial Mechanical Properties Of Carbon Nanotube Reinforced Nb/Nb₅Si₃ Composites

In recent years,carbon nanotubes have been regarded as the ideal reinforcement of composite materials because of their singular mechanical properties.They have attracted much attention of domestic and overseas scholars.The interface takes on the stress transfer between the carbon nanotubes and the matrix in the carbon nanotubes reinforced composites which plays a decisive role in the overall mechanical properties of the composites,and it has increasingly become the focus of research in the field of composite materials.In this paper,the carbon nanotubes reinforced Nb/Nb₅Si₃ composites were used as the object of study.The theoretical modeling of the carbon nanotubes reinforced Nb/Nb₅Si₃ composites was built from the vertical.Based on cohesive finite element method and composite homogenization theory,the interfacial stress transfer of composite material,the stress transfer of the carbon nanotubes reinforced body and the Nb/Nb₅Si₃ matrix were statistically analyzed under the state of complete bonding and debonding.Based on the above,the interfacial stress transmission and pull-out mechanism of single-walled carbon nanotube reinforced Nb/Nb₅Si₃ composites were simulated by ABAQUS.The effects of interfacial properties on the transverse mechanical properties of carbon nanotube reinforced Nb/Nb₅Si₃ composites were investigated.The results show that:1.The aspect ratio α and the elastic modulus ratio β of carbon nanotubes have significant effects on the interfacial shear stress of carbon nanotube reinforced Nb/Nb₅Si₃ composites both in the state of complete bonding and debonding.When α decreases,the distribution of the interface shear stress in the carbon nanotubes is more uniform and the stress transfer efficiency is higher in the above two states.When β decreases,the interface shear stress becomes smaller at the load end and becomes larger at the pull-out end in the state of complete bonding,and the maximum shear stress at the interface Only at the load end,will not be transferred to the pull out in the state of debonding.The effect of volume fraction Φ on the interfacial shear stress of carbon nanotube reinforced Nb/Nb₅Si₃ composites on the contrary that of β in the complete bonding state and has no effect on the debonding state.2.In the complete bonding state,the Vander Ed Ley and thermal residual stresses have an influence on the interfacial shear stress.The maximum interfacial shear stress obtained by considering Van Edward effect is smaller than that without considering.When the temperature decreases,the thermal residual shear caused by thermal mismatch stress makes the maximum shear stress of the load end increases,and the pull-out end decreases due to the superposition effect,and even the negative maximum shear stress is generated.The composites will lead to debonding when the negative maximum shear stress exceeds the interface ultimate strength.3.In the debonding state,the friction coefficient μ and the temperature difference ΔT have significant influence on the axial stress of carbon nanotubes and the interfacial shear stress of carbon nanotube reinforced Nb/Nb₅Si₃ composites.With the increase of the temperature difference and the friction coefficient of the interface,the axial stress of the carbon nanotubes decreases,while the interfacial shear stress increases,and the interfacial stress transfer efficiency is effectively enhanced.4.The maximum load required to pull out the carbon nanotubes increases with the increase of the aspect ratio or the interfacial strength,and the time required for debonding is also longer.The pull-out load will suddenly drop sharply when it reaches the limit value of interfacial,and the debonding process of the interface is very short.