Abstract: In a war environment, the damage of fuselage composite material would reduce its combat effectiveness. Therefore, restoring combat capability through repair is an urgent problem to be solved. In order to explore the law of strength recovery of repaired composite materials, the strength prediction model of scarf-repaired composite material was established based on cohesion model and finite element method, and the influence of defect size and repair slope on strength was analyzed. The results indicate that, the stress concentration occurs at the intersection of 0° and 90° layers, and the stress can reach 6.3 times the average stress. The stress concentration effect may be the initial cause of the damage of the scarf-repaired composite materials. With the increase of defect size, the repair strength decreases. The initial damage of the scarf-repaired composite material is mainly generated in the adhesive layer, then the damage develops along the interface when the defect size is larger than 3 mm. With the increase of repair slope, the strength shows an increasing trend. In terms of repair efficiency, the repair slope greater than 1∶15 meets the repair requirements. The research results provide a theoretical basis for the repair technique and efficiency evaluation of aircraft composite materials.

Key words: composite material, scarf-repair, cohesion model, defect size, repair slope