Parametric study on static and fatigue strength recovery of scarf-patch-repaired composite laminates

Carbon-epoxy composite laminate recovery rates are analyzed with respect to their static and fatigue strengths following local-damage repair using the scarf-patch bonding method. The tensile strength recovery rate is tested for 1.9-11.3° scarf angles (scarf ratios: 1/30-1/5). Static tests are performed for three external-ply overlap lengths and two defect sizes. The fatigue characteristics are identified via fatigue testing of a defect-free specimen and two specimens with different scarf angles. The static test results indicate that the strength recovery rate is significantly lower for scarf ratios of 1/10 or greater. Conversely, 1/20 and 1/30 scarf-ratio specimens exhibit high recovery rates of 79.1% and 83.6%, respectively, compared to the defect-free specimen. The external-ply overlap length and defect-size effects are negligible. For a million-cycle fatigue test, the fatigue strength recovery rates of the 1/20 and 1/30 specimens are 39.7% and 52.1%, respectively, being lower than the static strength recovery rate.