Fatigue studies on patch repaired carbon/epoxy woven composites

This work investigates the behaviour of carbon/epoxy composite laminates repaired by external patches under load controlled constant amplitude tensile fatigue loading. The specimens with laminate configurations [0 degrees/45 degrees/45 degrees/0 degrees] and [45 degrees/0 degrees/0 degrees/45 degrees] are repaired by bonding the pre-cured patches of two configurations viz. [0 degrees](2) and [45 degrees](2) over a hole made in the specimens, which mimic the damage on laminates. The strain field is captured by using Digital Image Correlation (DIC). The strain contours enable to develop understanding of the difference in compliance of both ([0 degrees](2) and [45 degrees](2)) patches under fatigue loading. The examination of repaired specimens during tests reveal that the damage initiates in the form of delamination and failure of patch-parent interface which grows further as the number of cycles increase and lead to ultimate failure. Moreover from life aspect, the external patch repair shows significant potential to restore life under fatigue loading. The damaged specimen (with hole) of [45 degrees/0 degrees/0 degrees/45 degrees] configuration has life of about 1k cycles, while the specimens repaired with [45 degrees](2) and [0 degrees](2) patches have a life of around 5k cycles and 2k cycles respectively. Furthermore, it is observed that for both parent laminate configurations, the specimens repaired with [45 degrees](2) patch have an overall higher life than the specimens repaired with [0 degrees](2) patch.