Shape optimization of scarf patch adhesive repairs for composite structures

To improve the repair performance of damaged composite laminates, a parametric optimization study was conducted on bonded scarf patch repair structures. A three-dimensional finite element model of a repaired composite laminate, including the parent laminate, adhesive layer and patch, was established. The tensile damage evolution of the scarf-repaired composite laminate was simulated using a compiled VUMAT subroutine combined with the three-dimensional Hashin failure criterion and cohesive zone method, and the reliability of the model was validated by comparison with experimental results reported in the literature. Based on this method, the effects of adhesive layer thickness, scarf angle, patch shape and size ratio on the mechanical properties of the repaired structure were further analyzed. The results show that the established finite element model can accurately predict the ultimate load of the repaired structure, with an error of less than 5% compared with the experimental results. With increasing adhesive layer thickness, the stress concentration in the adhesive layer becomes more pronounced, resulting in a gradual decrease in the ultimate strength of the repaired structure. Considering both mechanical performance and manufacturing feasibility, an adhesive layer thickness of 0.15 mm is considered reasonable. Increasing the scarf angle aggravates interfacial stress concentration and reduces the load-carrying capacity of the repaired structure; therefore, appropriately reducing the scarf angle is beneficial for improving the repair strength, while practical engineering conditions should also be considered. Patch shape and size ratio have significant effects on the repair performance, and the strength recovery rate of each patch type increases with increasing size ratio. Among the investigated patch shapes, the diamond-shaped patch exhibits better strength recovery. At the same size ratio, it achieves the highest strength recovery rate while significantly reducing the volume of removed material.