Effectiveness of the scarf repair considering an additional layer optimization for honeycomb sandwich structures with perforation damage

Perforation damage usually occurs in honeycomb sandwich structures, and to restore mechanical properties, the double-sided repair is required for damaged areas. Although it is convenient to directly bond external patches on the structure, the stiffness difference between the patch and original structure easily causes the interface delamination or secondary stress concentration. The scarf repair better restores the continuity of the original structure, but the removal of more materials leads to a larger damage range. The additional layer introduction regulates the stress distribution at the interface and enhances the bonding strength, but the repair effect is affected by the thickness, edge length, and ply angle of the additional layer. To improve this situation, a novel repair method that integrates the scarf repair with an additional layer optimization is proposed, and the influences on the bending and compression performance as well as the failure behaviors are studied for honeycomb sandwich structures with perforation damage. The 3D Hashin failure criterion is introduced to predict the damage initiation and propagation process of composite materials under different stress states, and the finite element models are established for the intact structure and the scarf-repaired structures with and without optimized additional layers. The response surface methodology combined with the Abaqus/Explicit module is adopted to optimize the side length, thickness, and carbon fiber ply angle of the additional layer. The mechanical properties and failure behaviors before and after repair are obtained through three-point bending and compression tests as well as finite element analysis. The results indicate that the double-sided repair with optimized additional layers effectively alleviates the stress concentration at the connection between the original structure and patches, and the experimental load-bearing, deformation, and energy absorption abilities increase by 38.5%, 20.6%, and 76.7% for bending as well as 18.6%, 24%, and 48.8% for compression, respectively.