Repair for CFRP laminates with mesh interlayers using resin pre-coating technique

Resin pre-coating (RPC) repair technique was applied to CFRP laminates with mesh interlayers and the restoration of strength and mode II interlaminar fracture toughness GII were evaluated. RPC repair is a resin infiltration technique utilizing low-viscosity acetone, making it effective for sharp delamination that cannot be fully repaired by the direct injection of high-viscosity resin alone. The objective of this study was to apply this repair technique to CFRP laminates that possess a complex mesh structure for interlaminar toughening, and to demonstrate that the presence of mesh interlayers enables further advancement of the RPC repair technique. To evaluate strength recovery, interlaminar delamination was generated intentionally by short beam test, then the RPC repair was applied, and its effectiveness was assessed through 3-point bending tests. Comparing the repair effectiveness with and without mesh interlayers, the specimen with mesh interlayers showed a higher recovery. Subsequently, 4-point End Notched Flexure tests were conducted to demonstrate the restoration of interlaminar fracture toughness GII. It was confirmed that GII during the crack propagation was restored in both laminates. Furthermore, simulating actual damage, repairs were also conducted against out-of-plane impact damage. Although the repair effectiveness could not be fully evaluated in mesh-inserted specimens due to fiber breakage that occurred during the impact loading, bending strength was improved in the specimen without mesh interlayers, and confirmed the effectiveness of the RPC repair to the impact damages.