Patch-repaired plain woven composite structures were exposed to internal damage caused by impact during service, which reduced mechanical properties. A multi-scale modeling strategy was proposed to study the impact resistance characteristics of patch-repaired plain woven carbon-fiber-reinforcedpolymer (CFRP) laminates. The micro representative volume element (RVE) was extracted from the yarn; a local homogenization method was used to obtain the equivalent cross-ply laminate (ECPL) cells corresponding to the mesoscale RVE. The finite element model (FEM) of patch-repaired plain woven laminate was established by extending the ECPL cells. The FEM was checked by the low-velocity impact (LVI) tests, and the impact parameter errors were within 10%. Furthermore, impact resistance of repaired specimens under different impact conditions (e.g., the impact energy was 3 $ 20 J) was studied. Finally, patch parameters (patch thickness, patch size, off-axis angle) of the repaired specimen were optimized by multi-objective optimization based on the surrogate model and response surface method (RSM). After multiobjective function optimization, the optimal patch parameter configuration (the thickness of the patch was 0.87 mm, the diameter was 66 mm, and the off-axis angle was 44.2 ) reduced the absorbed energy value of the repaired specimen from 4.9089 to 4.1640 J, and the delamination area of the repaired specimen from 605 to 280 mm 2 . All the results provide a reference for patch repair of plain woven composites.damage evolution, multi-objective optimization, multi-scale modeling, patch repair, plain woven CFRP composite
| INTRODUCTIONPlain woven carbon-fiber-reinforced-polymer (CFRP) composites have better interlaminar and in-plane strength due to their complex internal fabric structure, compared with unidirectional (UD) fiber composites. However, woven composite structures are vulnerable to internal damage caused by impact during service, which reduces mechanical properties. In order to reduce the maintenance cost, people often repair the damaged part of the structure to achieve the expected mechanical properties. Adhesive bonded repair 1,2 has been widely used in the repair of composite materials due to its ease of operation and less additional weight. The repair parameters of adhesive