Experimental And Numerical Study On Mechanical Properties Of CNT Fibers And Their Composite Interfaces

Carbon nanotube (CNT) fibers are a new kind of carbon materials, which arespun from aligned CNTs by particular manners. CNT fibers can be used as reinforcingmaterials or artificial muscles, and have broad potential applications in engineeringfields. To date, mechanical properties of CNT fibers, i.e., elastic modulus and strength,are still much lower than that of individual CNTs, which can be attributed to currentpreparation technique and other limiting factors. Therefore, basic research on CNTfibers are necessary for improving mechanical properties of CNT fibers. The researchcontents are as follows:(1) Monotonic and cyclic loading tests of CNT fibers were conducted. It isrevealed that tensile modulus, strength and failure strain of CNT fibers are greatlyaffected by tensile strain rate. Different micro-structural damage mechanisms of CNTfibers at different tensile strain rates were discussed base on SEM images.(2) Tensile tests were performed for CNT wires plied by two, three, four, five andsix CNT yarns. Relations between tensile modulus, strength and failure strain of CNTwires with ply numbers of yarns were discussed. In addition, micro-structuraldeformation of CNT wires and its corresponding nonlinear stage on force-straincurves were investigated. What’s more, load-strain curves of six-yarn CNT wires atthe same strain rates were measured. Morphologies of fractured surfaces of the CNTwires were shown by SEM images.(3) A clamping fixture was developed for microdroplet test of interfacialproperties between CNT fibers and PAA polymers. Force-displacement curves ofinterface between CNT fibers and PAA polymers were measured. The relationbetween maximum debonding force and embedded length of CNT fiber was discussed.Besides, finite element model of the micro-droplet test was built in softwareABAQUS. Cohesive finite elements were utilized for analysis of crack generation anddevelopment during debonding process of the interface. Interfacial shear stressdistributions of composite with different embedded length of CNT fiber wereinvestigated as well. Moreover, distribution of thermal residual stress caused bymatrix curing and its influence on interfacial strength of composite was investigated.At last, effect of cohesive parameters on debonding behavior of CNT composites were discussed.In conclusion, this thesis focuses on damage mechanism of CNT fibers and theirwires and properties of their composites. The present experimental and numericalresults will provide valuable a reference for preparation and application of CNT fibersand their composites.