Mechanical properties SWNT/epoxy composites

Figure 14.2. The mechanical properties of 0.5 wt% SWNT/Epoxy composites (a) tensile test of neat epoxy resin (b) tensile test of pristine-SWNT/epoxy ...

Another parameter influencing the mechanical properties of nanotube composites is the CNT alignment. The effects of CNT alignment on electrical conductivity and mechanical properties of CNT-polymer nanocomposites have been discussed in a number of researches [118-120]. For example, it has been reported that with increasing CNT alignment, the electrical and mechanical properties of the SWNT-epoxy composites increased due to an increased interface bonding of CNTs in the polymer matrix [119],... 

The first true mechanical study was made by Schadler et al. in 1998. They measured the stress-strain properties of a MWNT-epoxy composite during both tension and compression. In tension, the modulus increased from 3.1 GPa to 3.71 GPa on the addition of 5 wt% nanotubes, a reinforcement of d I7d Vf = 18 GPa. However, better results were seen in compression, with an increase in the modulus from 3.63 to 4.5 GPa, which corresponds to a reinforcement of 26 GPa. No significant increases in the strength of toughness were observed. The difference between tension and compression was explained by Raman studies which showed significantly better stress transfer to the nanotubes in compression than in tension. This can be explained by the fact that load transfer in compression can be thought of as a hydrostatic pressure effect, whereas load transfer in tension relies on the matrix-nanotube bond. However, it should be pointed out that later studies showed the reverse to be true, Le. load transfer in tension but none in compression.In further contrast, work by Wood et has shown that the mechanical response of SWNTs in tension and compression are identical. 

The development of ways to make SWNTs and control their structure as well as ways to manipulate them and incorporate them into devices is at the forefront of research in nanotechnology. Recent developments in CVD growth of nanotubes have resulted in the ability to grow bundles of CNTs that can be harvested and spun into fibers to make a super thread. The individual CNTs in a super thread are bonded by van der Waals forces, but it is possible to alter their mechanical and electrical properties by heat treating and irradiation. The sides of CNTs have been functionalized to bind with epoxies and polymers to form composites and their tips have been functionalized to serve as chemical sensors, atomic force microscope (AFM) tips, ion and electron emitters, and for other novel applications. 

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