Improved fatigue performance of nanostructured bidirectional fiberglass-polyurethane composites under uniaxial state and high deformations

Plates of composite material of bidirectional fiberglass [+/-45](4S) and nanostructured polyurethane matrix were manufactured using the Vacuum Assisted Resin Infusion (VARI) technique. Hydrophobic nanosilica (NS) was used at 1 and 2 wt. % loading. Even though the use of NS, the permeability of the perform did not increase substantially, obtaining high V-f (52%) and a good impregnation, as visualized with SEM. Uniaxial tensile tests under quasi-static conditions presented high deformations to failure (e(max)>10%), tensile strengths (RUTS) and elastic moduli (E) which decreased as a function of increased NS loading. On the other hand, the stress-controlled fatigue testings revealed that the addition of NS up to 2 wt. % improved fatigue performance. Specifically, the a and b constants of the empirical lineal model presented an increase of 77% and 92.7%, respectively. This improvement was corroborated through the measurement of the residual elastic modulus. Finally, the laminates presented an accumulation of inelastic deformation (ratcheting), whereas this phenomena was studied for two frequencies, 0.2Hz and 2 Hz.