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 degrees and 90 degrees 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 con?dence level was proposed to predict the fatigue life of scarf-repaired composites.