Fiber-reinforced composite materials have lower specific strength and specific gravity compared to metal materials. In addition, it has great durability, corrosion resistance so it was widely used in the aircraft, automotive, marine, marine and energy industries. Composite materials are also applied to shell-like structures such as pipes and pressure vessels based on formability and strength. In particular, research is being actively conducted to replace metal pipes with FRP pipes. FRP pipes can be produced through a variety of composite manufacturing processes. In particular, the filament winding process is mainly used for manufacturing pipes with high strength and fracture stability. Since the filament winding process can freely design a winding pattern, it is possible to manufacture a pipe suitable for the use environment. In general, a helical winding pattern is mainly used for excellent strength and to suppress the outflow of liquid or gas. However, the pipe of the helical winding pattern has a risk of completely cutting the entire cylinder after buckling so it is necessary to properly mix and use the helical pattern and the hoop pattern.
FRP pipes have an advantage that they do not corrode differently from metallic materials and have great chemical resistance. For this reason, it can be used in special environments such as water and sewage, industrial water, related water, ships, oil transportation, water storage, fire hydrant piping steel pipe, city gas, and liquefied petroleum gas supply steel pipe. In particular, steel pipes require a huge amount of time and cost to install and paint facilities, and to repair facilities due to aging. Therefore, FRP pipes are being developed to replace them. FRP is suitable for use in water but environmental degradation occurs in which the matrix material is separated from the strengthening agent. These factors directly affect strength degradation. Therefore, in this study, in order to increase the durability of the FRP pipe, the nanoparticles having a property of controlling the absorption of moisture were added to the manufacturing process of the pipe.
So in this study, a method of adding a hoop pattern and adding HNT to a helical pattern was used to fabricate a CFRP pipe suitable for use in an underwater environment with high strength. CFRP pipe specimens with two parameters were evaluated through bending test, interlaminar shear strength test, compression test, and moisture absorption rate analysis. As a result, the addition of a hoop pattern with a thickness corresponding to 8% of the helical pattern showed the most high mechanical strength through efficient transmission of bending and compression loads. Further hoop patterns have been shown to cause delamination of the helical and hoop layers. When the added HNT was evenly dispersed at the interface of the two patterns, the adhesion of the interface was increased to suppress the occurrence of peeling, which was most effective when the mass of the added HNT was 0.5%.