TENSILE FATIGUE PERFORMANCE OF CARBON-CARBON HYBRID QUASIISOTROPIC LAMINATE

This experimental study has been focused on the tensile-tensile fatigue performance of a carbon-carbon fiber hybrid quasi-isotropic laminate. The laminate contained two unidirectional carbon fiber prepregs with the same epoxy matrix. One prepreg had carbon fibers T800 for the high-elongation layer (HE), the other prepreg had carbon fibers DIALEAD for the low-elongation layer (LE). The sub-laminate stacking sequence was [HE/LE/HE]. Sub-laminates have been piled to get a quasi-isotropic layup [0/45/90/-45]s. The displacement (strain) controlled tension-tension tests were along the 0° fiber direction. Preliminary quasi-static tests provided the pseudo-ductile behavior considered for the fatigue loading levels. The evolution of the fatigue damage was macroscopically analyzed by the stiffness degradation, and microscopically by X-ray micro-CT observations. As main conclusions, the composite retains its load-carrying ability in the pseudo-ductile regime. The evolution of the fatigue damage involved fracture of 0° LE plies, transverse cracks in ±45° plies and delamination of 0°/+45°and ±45°/90° interfaces.