Effects of high-cycle fatigue on the viscoelastic properties of epoxy resin

In this work, the effects of high-cycle fatigue on the viscoelastic properties of a commercially available epoxy resin material were investigated experimentally. Specimens produced from neat epoxy material were split into two batches designated as pristine and fatigued. The specimens of the latter batch were subjected to a high-cycle fatigue loading under different stress amplitudes with a constant stress ratio of $R=\mathrm{0.1}$ until failure. The storage and loss modulus, loss factor, and glass transition temperature ($T_g$) of the pristine and fatigued specimens were measured using dynamic mechanical analysis. Complementary temperature-modulated differential scanning calorimetry was employed to analyze the changes in $T_g$ of the pristine and fatigued specimens. A systematic comparison of the pristine and fatigued materials strongly indicates that changes in the viscoelastic material properties before and after fatigue loading were statistically insignificant. The findings strongly corroborate the hypothesis that, within the tested stress ratio, the viscoelastic properties of the tested epoxy resin remain independent of the mechanically applied load cycles in the high-cycle fatigue regime.