Effects of Repair Interface Structure on Mechanical Properties of Scarf Repair for Composite Laminate Plates

The structural damage repair of composite material is an important issue that needs to be addressed during the service life of composite materials. To investigate the effects of a scarf structure and scarf angle on the repair quality of composite material, this paper proposes a mixed-scarf (MS) repair structure that combines ramped-scarf (RS) and stepped-scarf (SS) repair structures. The effect of the repair structure on the mechanical properties was analyzed, as well as the quality of the adhesive interface. The results show that at a scarf angle of 10°, the repair efficiency and the quality of adhesive interface are better than that of scarf angles of 20° and 30°. At a scarf angle of 10°, the recovery degree of the flexural strength of the MS repair structure is 79.72%, which is 6.77% and 38.24% higher than that of the RS and SS repair structures, respectively. However, in terms of flexural modulus, regardless of repair structure, the flexural modulus is highest at a scarf angle of 20°. Furthermore, the impact strength of the MS repair structure is approximately 87.60% that of the RS repair structure; additionally, it exhibits an increase of 45.83% compared to the SS repair structure. Overall, the quality of the adhesive interface for the RS and MS repair structures is similar and better than that of the SS repair structure. In conclusion, the MS repair structure is well suited for small-angle scarf repairs, whereas the RS repair structure is more appropriate for large-angle repairs; in contrast, the SS repair structure demonstrates the least effective performance in terms of repair outcomes.