Interfacial Transition Layer Construction And Its Effect On Interface And Fatigue Resistance Of Carbon Fiber Composites

With the wide application of carbon fiber reinforced resin matrix composites in various fields of national economy, people have put forward higher requirements on the interfacial and anti-fatigue properties of composite materials. However, due to the poor infiltration of resin and the performance mismatch between carbon fiber and resin matrix, interfacial debonding and earlier damage are more likely to occur under dynamic and static loading. Therefore, in this paper, based on the transition interphase theory, carbon nanotubes were introduced into the interfacial phase and the interfacial transition layer between the carbon fiber and epoxy resin was built. Furthermore, the reinforcing effect of this transition layer on the interfacial and anti-fatigue properties was also studied, providing new ideas for the preparation and improvement of multi-scale composites.First, to improve the dispersion properties of carbon nanotubes in water, oxidized multiwall carbon nanotubes (OCNTs) was prepared by using mixed-acid oxidation method. Then a continuous electrophoretic deposition method was used to deposit OCNTs onto the carbon fiber surface, and the content of OCNTs was controlled by adjusting the deposition time. Multi-scale reinforced composite materials were prepared by resin transfer molding technology. After the material mechanics performance tests, the shear and bending properties of the composites were found to depend strongly on the distribution state of carbon nanotubes in the interface region. When the electrophoretic deposition time was 5min, the distribution of carbon nanotubes in the fiber surface is relatively uniform, and the interfacial shear strength, interlaminar shear strength, flexural strength and flexural modulus of the composites were increased by 33.0%,10.5%,9.46% and 15.4% respectively compared those without OCNTs. However, when electrophoretic deposition time was extended to 7min, some OCNTs aggregates were found, and the LISS and flexural properties of the composites were slightly decreased. Besides, after about 30,000 times cyclic fatigue damage at bending mode, the residual bending strength retention the composites was improved by 3.3% compared with those without OCNTs. These facts demonstrated that both dynamic and static mechanical properties of muti-scale composites were improved.In order to clarify the reinforce mechanisms of OCNTs on composite materials, the element analysis function of scanning electron microscopy and the force modulation of atomic force microscopy were used to detect the composite interfacial structure containing OCNTs. It was found that the carbon element content and the relative modulus of the interface layer composed by OCNTs/epoxy resin were intermediate between epoxy resin and carbon fiber, indicating that the experimental method could be used to construct the interface transition layer between the matrix and the reinforcing filler. The interfacial transition layer with medium modulus could transfer the load effectively in the dynamic and static loading of the composites, thereby improving the mechanical performance of the composites.