Fatigue behavior of graphene nanoplatelets reinforced and unreinforced basalt/epoxy composite pressure vessels subjected to low-velocity impact under internal pressure

In this study, the fatigue behavior of 0.25 wt.% graphene nanoplatelets (GnPs) reinforced and unreinforced impact damaged basalt/epoxy composite pressure vessels (CPVs) was investigated. The CPVs were subjected to low-velocity impact (LVI) of 2.5 J, 5 J, 7.5 J, 10 J, 15 J, 20 J, and 25 J under internal pressure of 50 bar (hoop/axial prestresses: 98/49 MPa). Then, to detect fatigue life changes, fatigue tests were performed at load rates of 30% of ultimate hoop stress (sigma(HS)), where sweat damage occurred in the basalt/epoxy CPVs under alternating internal pressure. Considering the remaining fatigue life and formation of the damages in the CPVs for all impact energies, to investigate the fatigue behavior and GnPs effects of CPVs subjected to low-velocity impact, an impact value of 5 J was preferred. The 5 J impact damaged CPVs were subjected to fatigue cyclic following ASTM D 2992 at load rates of 20%, 25%, 30%, 35%, and 40% of the sigma(HS). The fatigue life of damaged CPVs was compared by that of undamaged over S-N curves. As the impact energy increased, the impact damage area increased. The increased size of damage reduced the fatigue life of basalt/epoxy CPVs. At the fatigue load rates mentioned above, the GnPs improved the fatigue life of damaged basalt/epoxy CPVs by about 3.5, 3.2, 11.3, 2.4, and 5 times, respectively.