Geometric and mechanical optimization in double-sided patch repair of carbon/epoxy laminates

Abstract

In this study, a numerical approach was adopted to optimize the geometric parameters of the patch and adhesive to improve the repair performance of a carbon/epoxy laminated composite structure. The studied laminate has a stacking sequence of [45/0/-45/90]s, representative of configurations commonly used in engineering. The analysis was performed using a three-dimensional nonlinear finite element method (FEM), applied to a notched composite plate subjected to tensile loading and repaired with a circular patch of the same material, placed on both sides. The existing literature focuses mainly on the separate evaluation of geometric or mechanical parameters, while the analysis of their interactions remains limited. Furthermore, the application of statistical methods such as design of experiments (DoE) for multi-parameter optimization of composite repairs remains marginal. It is in this context that the present study proposes a methodology integrating detailed 3D FEM modeling and multi-parameter analysis based on DoE, allowing the simultaneous evaluation of the influence of patch diameter, adhesive thickness, and shear modulus on the response of the repaired structure. The results show that mechanical strength increases with patch surface area, while excessive adhesive thickness reduces local stiffness. Among the parameters studied, the patch diameter is the dominant factor. The proposed approach is therefore a useful tool to improve the effectiveness and durability of bonded patch repairs.