Compressive fatigue behavior of external patch repaired carbon/epoxy composites

This work involves an experimental investigation of the external patch repaired woven carbon fiber-reinforced polymer laminates under load controlled constant amplitude compressive fatigue loading. The specimens of parent laminates with stacking sequence [0/45]s and [45/0]s were both repaired with two types of precured patches viz. [0]2 and [45]2 representing high stiff and low-stiff cases. Digital image correlation and acoustic emission were employed to obtain the insight to the development of distinctive failure modes. The observations during the tests reveal a slow increase in the displacement for most part of the life followed by a rapid increase in the displacement signifying the failure due to fatigue. The examination of failed specimens reveal failure through hole for drilled (with hole) specimens compared to failure away from repaired zone indicating the significant reinforcement provided by external patch repair under cyclic loading. From life aspect, the drilled specimens possess a significantly lesser life (zero to few hundred cycles) compared to the patch repaired and pristine specimens (of order of few thousand cycles) highlighting the suitability of the external patch repair to restore the fatigue performance under compressive loading.