Fatigue behavior of cross-ply glass-fiber composites based on epoxy resins of different toughnesses

The effect of matrix toughness on the fatigue behavior of cross-ply reinforced composites is discussed in this paper. Brittle and impact-modified epoxy resins containing commercial E-glass fibers with a good fiber matrix adhesion have been used. The fatigue behavior has been investigated by means of load-controlled tension–tension fatigue tests (R=0.1) and a frequency of 10 Hz with different applied max. loads between 150 and 330 MPa. The damage, as measured by stiffness reduction, was more significant for the composites with a brittle matrix. The energy loss was shown to be a sensitive tool for characterizing the nature of matrix toughness and is higher for impact-modified resins for a given strain amplitude. A non-linearity of the S/N curve was found for the impact-modified composites, while that for the brittle ones is linear on a semi log-scale. Furthermore, the brittle composites show an extensive region of final damage propagation, whereas the impact modified composites fail more in a sudden death manner.