Experimental investigation on scarf repair of damaged composite honeycomb sandwich structures with adhesively bonded carbon fiber-reinforced prepreg patches

Widely used in aerospace structures, composite honeycomb sandwich materials are costly and time-consuming to replace once damaged. Effective repair has become an essential approach for restoring function and extending service life. This study explored an efficient scarf repair strategy using adhesively bonded carbon fiber-reinforced prepreg patches. Facesheet-notched sandwich specimens were repaired with scarf patches, varying in scarf type, scarf angle, ply orientation, step pitch, and thickness of additional patches. Intrinsic modal frequency, compressive loading capacity, and strain distribution were employed to evaluate repair performance. A parametric analysis model based on analysis of variance was established to quantify the influence of each factor and guide optimization. Results show that the stepped scarf method outperformed the tapered one, especially when the scarf angle was lower than 1/20, due to its larger and more accurate bonding interface. Additional patch plies improved the load transfer by reinforcing the repair zone and providing overlapping paths with parent facesheet to redistribute stress. Among all variables, scarf angle had the greatest effect, followed by thickness, step pitch, and ply orientation. Specimens repaired with optimized parameters validated the accuracy of the quadratic regression model, and their load-bearing capacity was fully restored to the level of intact specimens.