Tension–tension fatigue performance and stiffness degradation of nanosilica

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