Effect of laser pretreatment on the adhesive strength, fracture toughness, and strain distribution of carbon fiber reinforced thermoplastics via mechanoluminescence visualization

In this study, for exploring laser pre-treatment conditions for improving adhesive performance, effect of laser treatment on CFRTPs was investigated by systematically controlling the photon density and feed rate of the laser pretreatment and considered the results through mechanical behavior using mechanoluminescence. There have been reports that laser treatment of FRP can reduce adhesion strength due to fragile LMWON or damage at fiber-matrix interface, but it succeeded that carefully selecting the laser treatment conditions can lead to the following remarkable improvements in adhesion performance. In terms of tensile shear strength (TSS) value with single lap joint (SLJ), it is found that laser treatment sample (24.5 MPa, cohesive failure: CF) exhibited similar value as plasma treatment as the conventional benchmark. Furthermore, the mode I fracture toughness (GIC) value in the DCB specimen with laser-treated CFRTP reached 1.35 kJ/m2, 10 times higher than that of untreated CFRTP, twice that of conventional plasma treatment, and reached that of the aviation CFRP-sheet epoxy adhesive (in the case of T800-3900-2B, FM309 adhesive).