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The aim of this study is to minimize the decrease in the mechanical properties of materials exposed to environmental conditions by adding nano additives, thereby increasing service life. It has been reported in the literature that boron nitride nanoparticles (BNNP), a multi-walled carbon nanotube (MWCNT), and hybrid (MWCNT + BNNP) nano additives improve the mechanical properties of FRPs and increase their lifetime. For this reason, in this study, filament wound BNNP, MWCNT, and MWCNT + BNNP hybrid reinforced carbon fiber epoxy composite pipes (CFRPs) were produced with (± 55°)4 configurations and 8 layers. Then, composite pipes were exposed to the hydrothermal aging process in distilled water at 80 °C for 7, 14, and 21 days in order to examine the effects of hot water absorption behavior on mechanical properties such as hardness, and density. The hardness and density measurements were realized in accordance with ASTM standards. The hardness, and density properties of water exposed BNNP, MWCNT, and MWCNT + BNNP hybrid reinforced and non-reinforced CFRPs were examined and compared with unexposed specimens according to ASTM standards. As a result of this study, it was observed that the hardness and density values of the specimens exposed to aging reinforced with nano-sized material were even higher than the hardness and density values of the neat epoxy unexposed to aging. Consequently, although water absorption caused a loss in the mechanical properties of the material, the negative effects of water absorption were minimized thanks to the added nano additives.

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Glass-reinforced plastic (GRP) composite pipes, the use of which has been increasing rapidly in many areas in recent years, may be exposed to the impact of different objects during assembly, operation, repair, and maintenance. Since composite materials are sensitive to impacts, it is vital to examine damage to the material. In this study, the repeated impact response of GRP composite pipes under internal hydrostatic pressure was investigated. In order to simulate different operating conditions on the GRP samples, a prestress was created by applying 4, 16, and 32 bar internal hydrostatic pressure. Then, the prestressed pipes were subjected to low velocity repeated impact tests. As a result of repeated impact tests at low velocity, changes in maximum displacement amount, maximum contact force, energy absorption capacity, and impact velocity were evaluated depending on the number of impacts applied to the samples. The changes in the strength of the samples subjected to repeated impact tests at different internal pressure levels were determined by the hoop tensile tests performed according to the ASTM D2290 standard. As a result of the hoop tensile tests, the variation of the material's tangential tensile strength and damage behavior according to impacts' number and the prestress were investigated.