Axial Fatigue Failure Sequence and Mechanisms in Unidirectional Fiberglas Composites

A study was conducted to determine the fatigue failure sequence and mechanisms of E-glass reinforced vinyl ester polymers in cyclic tension- tension axial loading. From the measurement of changes in modulus and hysteresis loop area, and from microstructural changes during the fatigue cycling, it was found that the onset of fatigue damage is caused by the fiber surface flaw propagations. These fiber surface flaws then coalesce to produce fiber surface crackings which in turn create interface failures. As the fatigue cycling continues, the interface failures induce matrix cracks which propagate in both transverse and shear directions. The fatigue speci men was found to fail completely by through-delamination parallel to the loading direction.