Ultrafast laser surface treatments for improved adhesion on carbon fiber-reinforced polymers

The surface preparation of carbon fiber-reinforced polymers (CFRPs) is crucial for effective bonding and profoundly affects joint quality and structural integrity. This study investigated the influence of the wavelength, pulse duration, fluence, and overscan number laser parameters on CFRP surface treatment and bonding performance. The extent of the resin residue and fiber damage on the CFRP surfaces following laser treatment was assessed utilizing image analysis software. The surface morphology of the CFRP was scrutinized using laser confocal microscopy and scanning electron microscopy (SEM). Contact angle measurements and X-ray photoelectron spectroscopy (XPS) were used to evaluate the surface wettability and chemical composition of the CFRP. The adhesive joint capabilities were rigorously tested to determine the causes of failures. The results revealed that laser treatment, which removed resin and integrated oxygen-containing functional groups, substantially increased the joint bonding strength. Notably, the femtosecond and picosecond green lasers at a fluence of 5.18 J/cm² significantly increased the shear strengths by 398.9 % and 393.9 %. A picosecond infrared laser at 3.69 J/cm² and a femtosecond infrared laser at 2.23 J/cm² achieved shear strength enhancements of 324.3 % and 337.9 %. Pre-treatment with a femtosecond green laser yielded the optimal shear strength. This study demonstrates that appropriate laser surface treatment can enhance CFRP bonding performance, particularly with the femtosecond lasers exhibiting superior shear strength enhancement. These findings offer a new strategy for efficient CFRP bonding and set the stage for further research to optimize laser parameters for broader industrial applications.