Experimental investigation of the fatigue properties ofbasalt/carbon/glass/epoxy hybrid composites under sea water environment

Nowadays, hybrid composites have been utilized in different sectors for critical structural parts due to their attractive properties like lower weight and higher strength & stiffness, better corrosion & wear resistance, and long fatigue life. On the other hand, fatigue is the most common cause of the structural collapse. Fatigue is a sudden failure of components below the maximum strength of the material when subjected to repeated loading. This thesis examines the influence of saltwater conditions on the tensile, flexural, and three-point bending fatigue properties of basalt, carbon, and glass fibers/epoxy hybrid composites. Five different composite plates: namely, Basalt/Epoxy (BE), Carbon/Epoxy (CE), Glass/Epoxy (GE), Basalt-Glass/Epoxy (BGE), and Basalt-Carbon-Glass/Epoxy (BCGE), were manufactured using Vacuum Assisted Resin Transfer Molding (VARTM). The PST 650 jigsaw cutter was used to prepare the specimens as per ASTM D3039 and ASTM D7264 standards, and then it was immersed in a saltwater solution for 60 days, 120 days, and 180 days before the tests. The tests were performed using an Instron 8801 UTM with a 100 KN capacity, and the repeatability of the experiment was observed by testing three samples from each category. Moreover, a special fixture is designed and manufactured to conduct the static and fatigue three-point bending test. The weight-gain curve, stress-strain diagram, the S-N curve, and stiffness degradation curves were plotted. Moreover, the effects of hybridization and saltwater conditions on the tensile, flexural, fatigue life, and bending stiffness loss were discussed. The result shows that all composite samples' tensile and flexural properties degrade as the conditioning period increases. For example, the tensile strength of BE composites degraded by 21.11%, while CE composites only decreased by 9.09%. In the same way, the maximum and minimum loss of tensile modulus is observed in BE (17.12%) and BCGE (8.68%) hybrid composites, respectively. The highest flexural strength and modulus loss are in BE (45.59%) and BCGE hybrid composites (11.18%), respectively. However, the tensile strength of the unconditioned BGE hybrid composites shows improvement over the GE, thanks to the involvement of basalt fiber. The fatigue test results reveal that bending fatigue properties of all composite samples show a degradation as the conditioning period on saltwater solution increases. Keywords: Basalt Fiber, Bending Fatigue, Carbon Fiber, Glass Fiber, Hybrid Composites, Mechanical Tests, Saltwater Effect, Three-Point Flexure