Karbon nanotüpler kullanılarak kompozitlerin mekanik özelliğinin geliştirilmesi: Nano-dikişli lamine kompozitlerin lamineler arası kayma mukavemetinin incelenmesi

Vertically aligned carbon nanotubes (A-CNTs) that are added into carbon fiber reinforced polymer matrix composite can significantly improve not only mechanical but also electrical properties of composites and called as hybrid or nano-engineered composite. Three common methods such as dispersion of CNTs into the polymer matrix, stitching them onto carbon fibers and synthesis CNTs onto fibers (fuzzy) are used to produce hybrid composites. In this study, A-CNTs which are synthesized using thermal chemical vapor deposition (CVD) are integrated by stitching directly onto carbon fiber surface after fabrication of custom made prepreg layers with carbon fibers. The custom made prepreg layers are made of nanotube reinforced epoxy matrix and carbon fibers. At the same time in this project, instead of performing higher number of experiments, experimental design which is called Taguchi L8 orthogonal array is preferred and also only 8 experiments (each experiment is repeated at least 5 times) are performed according to Taguchi design. At this design 7 different parameters which has 2 levels of each one are examined. Manufacturing method, epoxy type, dispersion solvent type, dispersed amount of CNT in epoxy and stitch types are selected as parameters. A-CNTs are synthesized on a Si substrate using CVD of C2H4/H2 at atmospheric pressure. The length of A-CNTs which is used to fabricate hybrid composites are around 80 μm with Raman measurements of (G/D ratio) about 2. During the hybrid composite fabrication A-CNTs are removed from the substrate without any damage with an easy delamination growth protocol and fully transferred onto the middle bidirectional carbon fiber ply. Three most important steps of the study can be summarized as the transfer printing of CNTs from substrate to reinforcement ply without disturbing orientation, homogeneous distribution of A-CNTs into epoxy and application of the mixture into the system. In our earlier studies, unmodified A-CNTs are dispersed using homogenizer and tip types ultrasonication in epoxy and alcohol (IPA, acetone etc.) respectively. After removed alcohol (if necessary) all dispersed CNTs are mixed using mechanical mixer in a low viscosity thermosetting resins which are consisted two components and a high viscose thermosetting resin (has a component). But some agglomerations are seen in these methods, so in this project magnetic stirrer is used for dispersion and achieved CNTs which is also called as bucky paper and this paper can be easily disperse to individual CNTs. This approach generally has the advantages of simplicity and high amount of CNTs can be dispersed on the contrary tip sonicator. A uniform distribution of CNTs during wetting is critical for composite properties. Samples are produced using hand lay-up/vacuum, and vacuum infusion process (VIP). Hand lay-up/vacuum and vacuum assisted resin infusion molding are a very attractive, cost effective and environmentally friendly method of processing composites. Experiments are performed to compare fracture behavior of the hierarchical composite with and without A-CNT. For the mechanical properties interlaminar shear strength (ILSS) of the samples are measured by short beam shear (SBS) test. In earlier reports it is stated that carbon nanotube reinforced composites have showed an improvement of 8-30% interlaminar shear strength by short beam tests. The addition of A-CNTs onto the carbon nanotube reinforced matrix and fiber composite is expected to show higher interlaminar shear strength properties. On the other hand before the experiments, the electrical conductivity of all samples are measured, to assess the potential as sensors for strain sensing for structural health monitoring (SHM). The stitch A-CNTs effects is investigated on the mechanical and electrical properties of composite as well as dispersed CNTs in epoxy. In the other section of thesis, vertically aligned multi walled carbon nanotubes (A-MWNTs) are synthesized with CVD method to create small dimension pore sized ultra narrow nano-exchangers for nano-particle and gas transfer through channels. As-grown A-MWNTs would have <2% volume fraction after the growth procedure and the rest is air (~98%). These structures would have high porosity and high permeability due to their structures with the CNT-CNT spacing between 80-100 nm depending on the catalyst and precursor system coupling. A micro device are fabricated with this A-MWNT and the nano-particle and gas exchange transfer will be studied with this context. The growth of A-MWNTs will be either in a continuous fashion as arrays or templated pillars that will help to characterize the effects of morphology on the efficiency of micro device.