Adhesive bonding of CFRP utilizing nanosecond laser texturing for pre-surface treatment in different processing environments

In this research work, a novel underwater laser surface texturing process has been introduced for improving the adhesive bonding strength of carbon fiber reinforced plastics (CFRP). Joining carbon fiber reinforced plastic (CFRP) sheets is a major challenge for many applications, including hydrogen tanks, aerospace systems, and automotives. Adhesive-based joining is not only simple but also has widespread applications. Surface preparation techniques play an important role in the adhesive joining of two components. In this research work, a nanosecond fiber laser was used to create three different types of textures (line, honeycomb, and grid) on 2.5 mm thick CFRP sheets before the application of adhesives. Textured samples were joined using epoxy-based adhesives, and joint strength was evaluated. The effect of the texturing environment (open air and static water) and texture design on joint strength was determined using lap shear strength tests. The fiber exposure, surface contact angle, roughness, and morphology of each sample were evaluated using a goniometer, confocal microscope, optical microscope, and scanning electron microscope. One-way ANOVA was performed using the Minitab software package to assess the statistical significance of laser surface texturing patterns and processing environments on key performance metrics. Fiber exposure in a sample was quantified and categorized into moderate, considerable, and complete exposure. Failed surfaces were examined to identify the type of failure. Finally, correlation based analysis of surface output parameters and adhesive bonding strength were performed. Surfaces prepared in water-assisted conditions had the highest strength in the case of grid texturing. In comparison, open-air processing produced the highest strength for honeycomb and line pattern designs. Overall, grid textures in water-assisted conditions resulted in the highest bonding strength.