Study on the Bending Properties and Failure Behaviors of Scarf-Repaired Honeycomb Sandwich Structures Considering the Optimal Design of an Additional Layer

The stress concentration occurs at the junction of the patch and original structure when the scarf-repaired honeycomb sandwich structure is subjected to the secondary impact, thus causing the local delamination and debonding in Carbon Fiber Reinforced Polymer (CFRP) panels. The introduction of an additional layer improves the strength and stiffness of scarf-repaired structures, but poor surface smoothness and larger uneven stress distribution occur after the dimensions of the additional layer increase to a certain extent. Hence, the optimal design of an additional layer is considered in the scarf-repaired structure to improve the load-bearing performance. The finite element models of scarf-repaired structures with and without an additional layer are established based on the 3D Hashin failure criterion, and the bending performance analysis is performed to obtain the maximum bearing load. An optimization model with the side length, thickness, and carbon fiber ply angle of the additional layer as design variables and the maximum bearing load as the design objective is built, and then is solved by the Response Surface Method (RSM). Three-point bending tests are conducted on the scarf-repaired carbon fiber composite-aramid paper honeycomb sandwich structures with and without an optimized additional layer. The results indicate that the optimized additional layer has made the load-bearing performance and deformation capacity of the scarf-repaired honeycomb sandwich structure significantly improve, that is, has effectively alleviate the stress concentration in the connection area between the patch and original structure.