Influence of the different surface treatments on fracture property of CFRP adhesive joint

Surface treatment before the bonding process for carbon fiber reinforced polymer composite (CFRP) laminate is an effective method to improve the adhesive bonding strength of the joint. In this paper, UV laser treatment and mechanical treatment were implemented to regulate the surface condition of CFTP laminate, and then the treated zone was characterized to research the reasons why adhesive joints exhibit different mechanical properties under various surface treatments. The surface resin was thoroughly and evenly removed by UV laser while the carbon fibers remained intact. Additionally, the UV laser treatment could reduce the contact angle of the CFRP surface, leading to an improvement in wettability and surface free energy. The CFRP adhesive joints treated by UV laser reach an average shear strength of 31.51 MPa, which is 42.32% greater than joints treated by mechanical grinding with an average shear strength of 22.14 MPa. The main fracture mode of the adhesive joint with UV laser treatment is the cohesive failure of adhesive film, as compared to the joint with mechanical treatment, whose fracture mode includes cohesive failure and adhesion failure between the adhesive film and CFRP laminate.