Enhanced fatigue behavior under internal pressure of CNT reinforced filament wound cracked pipes

In this study, the fatigue behavior of filament winding pipes was determined experimentally under internal pressure. Samples were produced by ultrasonication and the filament wound methods. In order to produce the CNTs/E Glass/Epoxy nanocomposite, CNTs and E-glass reinforcements and Bisphenol-A epoxy polymer matrix were used. Test specimens had antisymmetric six layers. All specimens had ±55° winding angle. During all the experiments, the surface crack, fatigue crack growth rate and reinforcement condition of carbon nanotube were investigated. Two different rates of CNT (0.5% and 1%) were compared with the pure epoxy material. Effect of CNT on fatigue life was investigated experimentally. Cracks on the pipes for the fatigue tests had the aspect ratio of a/c = 0.2 and crack depth range between a/t = 0,25 and 0,50. Each test was repeated at least 3 times. Three different maximum stress levels were determined for the tests, which were 40%, 50% and 60% of the ultimate hoop stress. Fatigue life of nanocomposite pipes was found to increase with enhanced inter-laminar adhesion via CNTs. Stopping crack progression, bridging mechanism and mechanical interlocking between fibers of CNTs had been justified by SEM images. As a conclusion, material properties of GRP pipes were discussed by determining the effect of the reinforcement of carbon nanotubes.