Interfacial Enhancement Mechanisms Of Carbon Nanotube/Carbon Fiber Multi-scale Composites

Compared with the traditional carbon fiber reinforced composites, carbonnanotube/carbon fiber multi-scale reinforced composite has excellent mechanicalperformance, such as the interfacial strength and toughness, which has potentialapplication value in aerospace and other high-technology fileds. However, there is alimited number of study in the interfacial enhancemengt mechanisms of thismulti-scale composites, such as the detachment of carbon nanotubes from carbonfiber surface and the pullout of carbon nanotubes from matrix. In this study, theabove two interfacial enhancement mechanisms are investigated by experimentaland theoretical methods. Then, based on the study of these two mechansims, a newtheoretical pullout model of carbon nanotube/carbon fiber multi-scale reinforcementfrom matrix was established. This study will provide theoreitcal basic on theapplication of this multi-scale reinforced composites.The carbon nanotube/carbon fiber grafting force was quantitativelydetermined. For the carbon nanotube/carbon fiber multi-scale reinforcement fromchemical method, there is a large range of strength from5to90MPa. Sometheoretical results show that the grafting force comes from van der Waals andchemical bonding interacitons. For the carbon nanotube/carbon fiber multi-scalereinforcement from chemical vapor deposition method, experimental results showthat there exists strong grafting force between the carbon nanotube and carbon fiberso that the carbon nanotube can be fractured.A peeling model based on continuum theory was established. In this model, thebonding types and the effect laws of angle between the carbon nanotube and carbonfiber were discussed. For the reinforcement obtained from chemical method, thebonding between the carbon nanotube and carbon fiber is composed of van derWaals and chemical bond interactions. The chemical bond contributes to the stronggrafting force, which is20times larger than the vdw der Waals interaction. Thereexists a relation of power function between the angle and curvature radius of carbonnanotube, which determines following rules: the effective interaction length betweencarbon nanotube and carbon fiber will decrease or increase when the angle increasesor decreases. The interface will break based on normal failure where the normalstress firstly reaches the maximum value when the angle is more than some criticalvalue; The interface will break based on shear failure where the shear stress firstlyreaches the maximum value when the angle is less than some critical angle. For thecarbon nanotubes, the grafting force based shear failure is more than the one basedon normal failure. A continuum pullout model of inclined carbon nanotube was established. Inthis model, the relation of rotation angle and inclining angle was established. Theeffect laws of elastic modulus, inclining angle, interfacial strengh, frictioncoefficient of CNT and compression strength of matrix in the relation of rotationangle and inclining angle, and curve of pulling load-displacement were discussed.The results show that the effect of friction coefficient in the relation of rotationangle and inclining angle can be neglected. When the inclining angle was fixed, therotation angle will increase with the increase of interfacial strength of carbonnanotube and matrix and compression strength of matrix, and decrease of elasticmodulus. The effect of elastic modulus in the maixmum pulling load can beneglected, however, the maixmum pulling displacement will increase with thedecrease of elastic modulus of carbon nanotube. The maximum pulling load anddisplacement increase with the increase of compression strength of matrix andfriction coefficient.