The effect of abrading treatment method on the bonding surface characteristics and fracture behavior of glass fiber-epoxy composite adhesive joints

Abstract

The effect of the mechanical abrading method on the bonding surface characteristics and fracture response of glass fiber-reinforced polymer (GFRP) composite adhesively bonded joints was investigated. Double cantilever beam specimens were manufactured by bonding GFRP substrates with an epoxy adhesive to evaluate the mode-I adhesive joint fracture response. The bonding surfaces were treated with degreasing and abrading methods utilizing sandpapers with various grit sizes ranging from P60 to P800. The results showed that the sandpaper grit size can considerably change the bonding surface properties comprising the surface energy, roughness, morphology, and water drop contact angle and consequently, it can affect the joint fracture behavior. Reducing the sandpaper grit size continuously increased the surface roughness but there were optimum values for the surface energy and water drop contact angle. The fracture resistance of adhesive joints followed the trend of bonding surface energy as the higher the bonding surface energy, the higher the joint fracture resistance. The fracture energy and load-bearing capacity of adhesive joints were improved by 62 and 34%, respectively, when the joint bonding surfaces were abraded with P240. However, further reducing the sandpaper grit size to P60 caused a decrease in the fracture energy and load-bearing capacity of adhesive joints by 18 and 44%, respectively, compared to the joint with degreased and non-abraded bonding surfaces. Moreover, the abrading method considerably changed the microscopic and macroscopic failure modes of adhesive joints.