Effect of adhesive modification and surface treatment of laminates on the single lap bonding joint properties of carbon fibre composites

In this study, the effects of adhesive modification, surface treatment of laminates, and their combined effects on the bonding properties of adhesive joints were studied using tensile shear tests, SEM micro-morphology characterisation, EDS energy spectra, analysis of the load-displacement curve, failure mode, and element content on the bonding surface. The test group corresponding to surface treatment of the laminate exhibited the best tensile shear performance. Surface treatment by 20% NaOH increased the tensile shear strength and failure displacement by 30.41% and 106.72%, respectively, compared to that obtained with only surface polishing using 320# sandpaper. In the adhesive modification test group, the tensile shear strength of the joint was the largest with an adhesive modification by 3 wt.% short glass fibres, while the tensile shear strength and failure displacement increased by 7.96% (18.63 MPa) and 10.2%, respectively, compared with those without adhesive modification. To further improve the wettability and interfacial bonding strength between the glass fibre and adhesive, a 3 wt.% short glass fibre was pretreated with KH-550 silane coupling agent. The tensile shear strength of the joint improved to 19.06 MPa, and the maximum failure displacement was 1.59 mm, which were 2.31% and 2.58% higher than those without KH-550 silane coupling agent pretreatment on the glass fibre, respectively. Furthermore, adhesive modification by KH-550 treated 3 wt.% short glass fibre was underwent combining with laminate surface treatment with 20% NaOH. The bonding strength was higher than that obtained using 3 wt.% GF adhesive modification pretreated with KH-550, while lower by 10.49% compared with that corresponding to the surface treatment of the laminate by 20% NaOH. This was primarily attributed to the pores produced by the hydrolysis reaction between NaOH and the KH-550 silane coupling agent, which weakened the load-bearing capacity of the joint.