The aim of this study is to investigate the influence of nanosilica on glass-reinforced epoxy composites under static mechanical and tension–tension fatigue loading. The glass-reinforced epoxy composites were manufactured with three different concentrations of nanosilica (6, 7, and 8 wt%). Static mechanical tests include tensile, flexure and short-beam strength. 6 wt% nanosilica composites showed the greatest enhancement in tensile strength, percentage elongation, and inter-laminar shear strength compared to the other concentrations and the control. Extensive tension–tension fatigue tests (R-ratio of 0.1 and frequency 2 Hz) were conducted on the control and 6 wt% nanosilica composites. In load-controlled and constant amplitude tests, a percentage of the ultimate tensile strength was applied to the specimens. Stress applied was from 80% of UTS, and reduced in steps of 10% until specimens survived 1 million cycles. In high-cycle and low-cycle fatigue tests, 6 wt% nanosilica composites showed 10 and 3 times improvement in fatigue life, respectively, compared to the control composites. Stiffness degradation curves were explained with three stages of damage mechanisms. The final failure occurred due to fiber breakage in the third stage. Both the control and 6 wt% nanosilica composites survived 1 million cycles at a maximum stress of 46.6 MPa, but at the end of 1 million cycles, control composites lost 65% modulus compared to 45% modulus loss in the 6 wt% nanosilica composites.

Polymer matrix composites (PMC), often referred to as fiber reinforced plastics (FRP), consist of fiber reinforcement (E-glass, S2glass, aramid, carbon, or natural fibers) and polymer matrix/resin (polyester, vinyl ester, polyurethane, phenolic, and epoxies). Eglass/polyester and E-glass/vinyl ester composites are extensively used in the marine, sports, transportation, military, and construction industries. These industries primarily use low-cost open molding processes, such as manual/spray lay-up. Polyester and vinyl ester resin systems produce styrene emissions. Because of the stringent EPA regulations on styrene emissions, composite manufacturers are interested in using low-cost closed molding processes, such as vacuum-assisted resin transfer molding (VARTM) and styrene-free resin systems such as non-foam and full-density polyurethanes (PUR). Polyurethanes are polymers created by addition of polyisocyanates and polyols. The polyol component in polyurerhane can be produced from soybean oil. This study demonstrates that with the proper addition of nanoparticles, mechanical properties of soy-based polyurethane can be enhanced. These nanomodified soy-based polyurethane/glass composites manufactured by using the low-cost VARTM process provide alternatives to traditional glass/polyester and glass/vinyl ester composites. These composites will be more environmental friendly for two reasons: (a) Polyurethane does not produce styrene emission, thereby, resulting in a safer work place and (b) Polyol is made from a renewable resource (soybean oil).