The effects of graphene reinforcement on the fatigue behaviors of low velocity impacted and non-impacted basalt fiber reinforced composite pressure vessels

In this study, the fatigue behavior of filament winding basalt/epoxy composite pressure vessels with 0.25% graphene nanoplatelets (GnPs) reinforced and non-reinforced [±55°]4 configuration was investigated by modeling under close-ended conditions over basalt/epoxy composite pipes. The fatigue tests of the samples were performed at 25 cycles/min (0.42 Hz) and 0.05 stress ratio (R) under close-ended internal pressure experimental conditions according to ASTM D 2992-18. Fatigue tests were performed at loading rates of 30%, 35%, 40%, 50%, and 60% of the maximum tangential stress (σt_max) where leakage damage occurred in the form of sweating in the composite pressure vessels. The order and formation of the damage was determined by observing damages generated during fatigue tests. These damages resulted in sweating (slight initial leakage), leakage (intense leakage on the surface) and burst (layer separation and fiber fracture). The fatigue curves were drawn by using fatigue loading rates and failure cycles according to the type of the damage. Filament winding composite pressure vessels are widely used in space, aerospace, defense and automotive industries. Composite pressure vessels serving risky and critical tasks can be subjected to low-velocity impacts under service conditions. Damages generated in the fiber, matrix, and/or between layers after impact can lead to a decrease in the fatigue life of composite pressure vessel. In order to investigate the effect of low velocity impact damage on fatigue life, the changes in fatigue life by using loading rate of 30%σt_max were determined the basalt/epoxy and GnPs/basalt/epoxy composite pressure vessels damaged by 2.5, 5, 7.5, 10, 15, 20 and 25 J impact energies under 50 bar internal pressure. The dynamic behavior of the composite pressure vessels during the low velocity, impact and fatigue damages were examined. Then, impact value of 5 J was selected considering remaining life cycles and formation of the damages in the samples after the impact. The fatigue life of basalt/epoxy and GnPs/basalt/epoxy composite pressure vessels with low velocity impact damage of 5 J under close-ended internal pressure were compared with their undamaged. In conclusion, the fatigue behavior of low velocity impact damaged and undamaged basalt/epoxy and GnPs/basalt/epoxy filament wound composite pressure vessels under close-ended internal pressure conditions were determined and discussed.