| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 103 === This study is focuses on the characteristics of the benzoxazine/epoxy copolymer matrix, combined thegraphene and micro-scale short carbon fibers to be reinforcement. In order to investigate the reinforced mechanism of the nano-scale and micro-scale additive, the interfacial properties, mechanical behavior, and fatigue failure would be realized on the mulit-scale reinforced composite. The researches includes: (1) Different contents of benzoxazine resin in Epoxy resin, (2) graphene and Micro-scale short carbon fibers concentration, (3) the interaction of multi-scale reinforcement material concentration
This research aims to discuss the effect of the mixture of nano-scale graphene and micro-scale short carbon fiber, notably intensifies the the mixture of multi-scale interface, improving and increasing both mechanical properties and dynamic fatigue life. The investigation includes:(1)Different Benzoxazine resin concentration in Epoxy,(2)Nano-scale graphene and Micro-scale short carbon fibers concentration.(3)Multi-scale reinforcement material concentration.
In the matrix experiment, the results indicate that the value of mechanical strength increases with the content of benzoxazine increased. From the results, the 20wt% benzoxazine/epoxy significantly improves the mechanical strength up to 21.37% improvement in tensile strength; 33.45% improvement in flexural strength; 13.86% improvement in flexural modulus; 38.03% improvement in resistance of water absorption.
However, because of the property benzoxazine is more brittle than epoxy, the impact strength of benzoxazine/epoxy copolymer reduces about 55%.
The research shows that addition of graphene in the optimum content of 20wt% benzoxazine/epoxy composite 14.18% improvement in tensile strength, 22.83% improvement in the resistance of water absorption by adding the 0.5wt% graphene; 2.46% improvement in flexural strength, and 8.05% improvement in flexural modulus by adding the 0.25wt% graphene.
It is showed that adding 8wt% micro-scale short carbon fiber has the best enhancement to the mechanical properties: increasing 22.93% in flexural strength and 9.84% in the resistance of water absorption.
Finally, the optimum content of GNPs-0.5wt%/SF-8wt%/ Benzoxazine/ Epoxy composites preform the best enhancement to the properties about 22.62% improvement in tensile strength, 12.2% improvement in flexural strength, and 39.07% improvement in impact strength, 3.2-3.8 times improvement in torsion fatigue life. Because of the reason of short carbon fiber will produce a lot of micro-cracks in the fiber-end, the stress concentration would influence the ductility and lead to cracks propagation. In the result, the flexural tests reveal about 33.84% downtrend in flexural modulus.
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