Bonding repair of CFRP based on cold plasma treatment surface modification

The surface pretreatment before bonding repair determines the microscopic physical and chemical properties of the composites, and directly affects the bonding strength and maintenance effect. In this paper, the surface of the Carbon Fiber Reinforced Polymer (CFRP) was pretreated by Cold Plasma Treatment (CPT) under 2.5 times air atmosphere (0.25 MPa) to achieve the best interface micro-performance for bonding repair. Based on the surface microstructure and surface activity test, the single lap test was used to evaluate the bonding repair strength after surface modification. The results show that the optimized surface treatment parameters of the output power, the plasma flame-core distance, and the process time were 800 W, 7 mm, and 7 s, respectively. It is found that no damage to the fiber and the surface-free energy of the pretreated composites (800 W, 7 mm, 7 s) reaches 51.65 mN/m under the optimized process, which is higher than those of the untreated original value 43.83 mN/m and the manual-grinding treatment value 45.73 mN/m. The bonding strength of CFRP after CPT treatment was increased to 11.31 MPa, which was obviously better than the bonding strength of 7.11 MPa without pretreated specimen and the bonding strength of 8.14 MPa after manual-grinding treatment. The failure mode of samples after CPT treatment was cohesive failure, while those of manual-grinding treated and original untreated CFRP samples exhibited thin layer cohesive failure (TLC) and adhesion failure (ADH), respectively.