Fatigue performances and reliability analysis of fatigue life for scarf-repaired composite laminates

This paper focuses on the fatigue performances and reliability analysis of fatigue life for scarf-repaired carbon fiber composite laminates, which plays an important role in ensuring the safety of repaired aircraft. Tension–tension fatigue tests at constant-load amplitude were conducted to determine the fatigue limit and mechanism of scarf-repaired composite laminates. Experimental results show that the fatigue limit of scarf-repaired composite laminates is about 34% of the static tensile strength and the failure modes of speicmens under different stress levels are similar. The dominated failure mode is cohesive failure of adhesive, accompanied by partial 45° and 90° matrix cracks of composite patch. Meanwhile, the stiffness degradation and crack observation indicate that the crack initiation stage occupies a large proportion (92 ± 5%) of fatigue life. In additon, the distribution of fatigue life data was discussed. Based on the best fitting distribution, a new approach incorporating both reliability and confidence level was proposed to predict the fatigue life of scarf-repaired composites.