Effect of Silica Nanoparticles on the Fatigue Life of a Glass Fiber Reinforced Epoxy Composite Under an Aircraft Spectrum Load Sequence

Abstract

Two types of glass fiber reinforced plastic (GFRP) composites viz., (i) GFRP employing unmodified LY556 epoxy matrix (GFRP-neat), and (ii) GFRP incorporated with 10 wt% of well-dispersed silica nanoparticles in the LY556 epoxy matrix (GFRP-nano), were tested to determine their fatigue life under mini-FALSTAFF, a standard fighter aircraft spectrum load sequence. Spectrum fatigue tests were conducted on standard test specimens in a 50 kN servo-hydraulic test machine with sinusoidal waveform at an average frequency of 3 Hz. Tests were conducted on both types of GFRP composites with various reference stresses to determine the fatigue life expressed as number of blocks required for failure. The fatigue life of GFRP-nano composite was observed to be about four times higher than that of GFRP-neat composite over the entire range of reference stresses investigated. For a given number of applied load cycles, both the matrix crack density and stiffness reduction rates were observed to be lower in GFRP-nano composite when compared to that of GFRP-neat composite. Presence of silica nanoparticles in the epoxy matrix of GFRP appear to reduce matrix cracking and also retard crack growth rate in the composite leading to enhanced fatigue life. Further, using constant fatigue life diagrams of these materials, the spectrum fatigue life under mini-FALSTAFF load sequence was predicted. Good correlation was observed between the predicted and experimental fatigue life for both types of composites.