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Effects of the PopTube Approach CNT Synthesis Process on the Tensile Properties of Carbon Fibers and their Composites



In this study, the effects of CNT growth on the tensile properties of carbon fibers and their composites are examined. A novel CNT synthesis method – the PopTube Approach – is used to grow CNTs directly on carbon fibers. This technique utilizes microwave irradiation to synthesize CNTs on carbon fibers using the organometallic compound ferrocene as both the catalyst and primary carbon source. To study the effects of the CNT growth process at the fiber level, CNTreinforced single fibers are harvested and tested for tensile strength. To study the effects of the CNT growth process at the composite level, CNT-reinforced woven carbon fiber fabric is used to produce laminate composites – which are also tested for tensile strength. In both components of this study, control groups are tested for comparison. Single fiber tensile tests are carried out according to ASTM D3379, while composite tensile tests are carried out according to ASTM D3039. Results show that single fiber tensile strength is reduced on the order of 10% as a result of the CNT growth process. This suggests that the CNT synthesis process causes some degree of damage to the fibers themselves, which is perhaps to be expected. Composite tensile strength, however, is reduced on the order of 30%. Factors contributing to this decline at the composite level are identified and examined. Along with damage to the fibers and a reduction in fiber volume fraction due to the presence of CNTs, a shift in failure mode is observed in the CNT-reinforced composites as a result of the increased interfacial shear strength provided by the CNTs. These observations suggest that a tradeoff may exist in CNT-reinforced composites between the desired improvements in delamination resistance and the undesired reduction of in-plane tensile properties.

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