Correlation between interfacial bonding behavior and surface treatments in bonded carbon fiber composite joints

Surface treatments play a crucial role in enhancing the bonding strength of composites. The effect of surface treatment has received much attention in the literature but reported effect of combined treatments are less prevalent. Therefore, this work explored the correlation between plasma, sanding, porous release film treatments, its combination and bonding behavior in bonded carbon fiber composite joints. The bonding performance of composites was predominantly affected by three mechanisms: chemical cross-linking, chemical adsorption and mechanical interlocking. The bonding strength was enhanced after plasma treatment through the increased polar functional groups and surface wettability, resulting in a 7% (28.6 MPa) improvement compared to untreated samples. Sanding and porous release film treated surfaces exhibited increased roughness and mechanical interlocking, with strength up to 29.5 and 38.7 MPa enhancement in shear strength. Furthermore, plasma and sanding treatments removed surface contaminants and enhanced the bonding strength. Plasma treatment on surfaces treated with porous release film led to a slight decrease in bonding strength (35.9 MPa), as the deep valleys were changed into shallow ones by plasma. Spearman correlation analysis was used to establish the relationship between characterization parameters and shear strength. The results revealed a robust correlation between surface roughness and strength, highlighting its potential for predicting bonding performance.Highlights Comprehensive investigations on the correlation between surface treating techniques and bonding behaviors. The shear strength increased as the integrity of adhesive film decreased. Roughness has the most robust correlation with shear strength.