Effect of re-depositions and fiber exposure on the adhesive bond strength of CFRP after UV excimer laser treatment

Adhesive bonding of CFRP is one major approach to join this class of compound materials with other components, e.g., metals. The necessity to clean CFRP parts after fabrication and generate a bond-ready interface without damaging the implemented fibers demands a gentle and highly reproducible surface treatment. Lasers operating in the UV region are one promising technique for that topic. Yet, the factors influencing the adhesion properties of laser-treated CFRP are not sufficiently understood. The present paper describes the influence of nanosecond-pulsed laser parameters on CFRP treatment effects in context of adhesive bonding properties. A special focus was given on the distribution and avoidance of re-deposition effects by laser parameter selection. Furthermore, the effect of laser-induced fiber exposure was analyzed. Re-deposition and fiber exposure were complementarily discussed with chemical analyses of the surface composition after laser treatment in the context of bond strength studies under Mode I loading. It was found that both effects, i.e., re-deposition on the treated surface and laser-induced fiber exposure by overtreatment, result in lower strength values compared to an “optimized” treatment exhibiting none of the descripted conditions.