Estimation of Fatigue Life of Epoxy-alumina Polymer Nanocomposites

Epoxy alumina polymer nanocomposites were synthesized by in-situ polymerization technique. Dispersion of rod shaped alumina nanoparticles, having a length less than 50 nm and diameter in the range of 10 nm, in the epoxy matrix was achieved using ultrasonication. Nanocomposites having 0.5, 1 and 1.5 wt % of alumina nanoparticles were prepared. Good dispersion of alumina nanoparticles in epoxy matrix was observed through transmission electron micrographs of the nanocomposites. Tensile properties and the fatigue life of the nanocomposites were determined. Elastic modulus and tensile strength of the nanocomposites increased up to 1% weight fraction of alumina particles over that of neat epoxy and slight reduction in the elastic modulus and tensile strength of the nanocomposites was observed on further addition of alumina nanoparticles. Fatigue life of nanocomposites was investigated for constant amplitude tensile fatigue load (R=0.1). It was observed that the addition of alumina nanoparticles provides good improvement in fatigue life of epoxy. An increment of three to four times in the fatigue life of nanocomposites having 1.5% alumina particles was observed over that of neat polymer at low stress levels. Whereas increment in fatigue life of nanocomposites decreased at higher stress level (at stress level of 0.5 times that of tensile strength of neat epoxy). Fracture surfaces of specimens in fatigue were examined with the help of scanning electron microscope in order to investigate mechanisms responsible for the increase in fatigue life. Roughness of fractured surfaces of nanocomposites were more in comparison to that of neat epoxy showing consumption of higher energy for fatigue failure causing an increment in the fatigue life of nanocomposites.