Objectives Marine fiber-reinforced composite sandwich panels are widely adopted in ship and ocean engineering for their outstanding mechanical properties, yet they are vulnerable to damage during long-term service. At present, insufficient research has been conducted on their post-repair performance, especially the in-plane compressive behavior after repair. This study aims to evaluate the recovery effect of scarf repair on the in-plane compressive performance of such panels, reveal the damage evolution and failure mechanisms, analyze key repair parameters, and provide theoretical basis and engineering guidance for repair practices.

Methods Intact specimens, specimens with single-face skin damage, and repaired specimens were prepared in accordance with the ASTM D7137 standard, followed by axial compression tests. A progressive damage finite element model was established via Abaqus. The Hashin failure criterion, volumetric hardening model, and cohesive zone model were used to characterize intralaminar damage, core material mechanical behavior, and interfacial debonding, respectively. Mesh convergence analysis was performed to balance computational accuracy and efficiency, and the model was validated by comparing numerical results with experimental data.

Results The developed model is highly reliable, with a prediction error of ultimate bearing capacity below 7% compared with test results. The dominant failure modes of the repaired structure are debonding at the patch edge and fiber fracture, accompanied by local core buckling and adhesive layer failure. The scarf angle and intermediate layer size dominate the repair efficiency, while the patch layup direction has a negligible effect. Excessively large or small scarf angles cause severe stress concentration and reduced stiffness, respectively; increasing the intermediate layer size mitigates stress concentration with a diminishing beneficial effect, and optimal performance is achieved when the patch layup matches that of the parent panel.

Conclusions The optimized repair parameters are determined as a 1∶10 scarf angle, an intermediate layer with a diameter 1.2–1.3 times that of the patch, and a patch layup identical to the parent panel. With this combination, the bearing capacity of the repaired panel reaches 87.7% of the intact panel. This scheme reduces material consumption and cost while ensuring structural strength, and is applicable to the in-plane compression repair design of marine composite sandwich panels with single-face skin damage.