Mechanical characteristics of continuous carbon nanotube and continuously reinforced carbon nanotube composite
| Author(s) | Li, Yupeng | |
| Date Accessioned | 2017-01-12T12:46:08Z | |
| Date Available | 2017-01-12T12:46:08Z | |
| Publication Date | 2016 | |
| Abstract | Due to the outstanding mechanical, thermal and electronic properties of carbon nanotubes (CNTs), CNT and CNT reinforced polymer composite are becoming more and more pervasive in engineering applications, especially in energy absorbing and damping materials. Therefore, the underlying mechanism of the intriguing mechanical properties of CNT arrays and CNT reinforced composites is an essential and fundamental science for the potential applications of CNT related materials. It is fundamental and critical to investigate the mechanical properties of CNTs first, since the intrinsic properties and collective behavior of CNTs play an important role in the mechanical response of composite. The buckling behavior of vertically aligned carbon nanotubes (VACNT) was investigated. By taking van der Waals interactions into account, both experiments and modeling results confirm that VACNTs buckle in the bottom region with a high mode buckling, following wave damping effect. Then, the compressive behavior of VACNTs was quantified by strain energy density function. The effects of CNT structure/morphology, including diameter, cross section area, moment of inertia, defect degree and density, on mechanical properties were statistically investigated and compared with cellular materials, showing significant influence on determining the mechanical properties of VACNTs. The focus of CNT polymer composites is on the application-oriented viscoelastic properties. The static viscoelastic characterization was conducted by creep and stress relaxation tests with stress/strain variation and quantified by nonlinear power-law model. The dynamic properties were characterized by dynamic mechanical analysis (DMA) with frequency variation. And CNTs show significant enhancement in elastic response and considerable influence on viscous response. In addition, the temperature effects were investigated and composites show better thermal stability. By using timetemperature superposition (TTS) and Williams–Landel–Ferry (WLF) fitting, the prediction scale of viscoelastic behavior in time/frequency range can be significant enlarged. The viscoelastic responses are complicated by the intrinsic anisotropy of CNTs, so it is also essential to study their anisotropic properties. The compressive and viscoelastic characterization were performed on longitudinal, transverse and random composites and compared with PDMS. The results confirm the exceptional reinforcement of CNTs in longitudinal composites, which have lateral support from polymer matrix. And the increased damping effects of composites can be explained by the interfacial sliding and the energy dissipation between nanotubes and polymer matrix. Furthermore, the fatigue tests of CNT polymer composites were performed to investigate mechanical robustness and long-term stability. From the stress-number of cycles (S-N) data in cyclic DMA tests, CNTs improved the fatigue life of composites considerably, especially in high-cycle fatigue strength, caused by the hindering of crack propagation from CNTs, the interface debonding and the CNT reinforcement effects. Also, the microscopy images of fracture surfaces indicate different fatigue resistance and different fracture/crack mechanism between longitudinal and transverse composites. | en_US |
| Advisor | Suhr, Jonghwan | |
| Advisor | Wei, Bingqing | |
| Degree | Ph.D. | |
| Department | University of Delaware, Department of Mechanical Engineering | |
| Unique Identifier | 968209603 | |
| URL | http://udspace.udel.edu/handle/19716/19964 | |
| Publisher | University of Delaware | en_US |
| URI | http://search.proquest.com/docview/1823265661?accountid=10457 | |
| dc.subject.lcsh | Carbon nanotubes -- Mechanical properties. | |
| dc.subject.lcsh | Nanocomposites (Materials) -- Mechanical properties. | |
| Title | Mechanical characteristics of continuous carbon nanotube and continuously reinforced carbon nanotube composite | en_US |
| Type | Thesis | en_US |