Investigation of the differences between photochemical and photothermal laser ablation on the shear strength of CFRP/CFRP adhesive joints

Ensure high bonding strength and durability is very important for composite materials that are widely used by many different industries. In order to achieve this, the surfaces of the composite materials should be prepared for the adhesion process. Surface preparation with laser is a promising technique for the adhesive joint. However, the diversity offered by the advances in laser technologies and the multiplicity of parameters that must be controlled in laser material processing makes the process somewhat complex. In the present study, two different lasers have been used with different wavelengths (355 nm (UV) and 10600 nm (IR)) and pulse durations (4,4 ns and 5 mu s), to increase the lap shear strength of the adhesive joint of carbon fiber reinforced polymer (CFRP) materials. While the ultraviolet (L V) laser with high photon energy creates photo-chemical ablation, infrared laser (IR) causes photo-thermal ablation due to their low photon energy. CFRP samples treated with different lasers and the accumulated laser fluences have been adhesively joined and the results evaluated experimentally. According to the results, differences in laser ablation mechanism cause structural differences on CFRP surfaces. While resolidified epoxy was observed on CO2 laser treated surfaces, no residues were detected on UV laser treated surfaces. However, to avoid delamination or fiber damage risks an optimization of laser parameters are recommended to be performed for both laser systems.