An investigation to compare the shear strength of the adhesive joint of unidirectional CFRP after KrF excimer laser treatment in normal atmosphere, argon and underwater environments

Abstract

Unidirectional CFRP was treated by KrF laser in normal atmosphere, argon and underwater environments, before adhesive bonding. KrF laser removed the top resin layer and exposed the carbon fibres. Porosity and holes were generated around exposed carbon fibres after argon environment treatments and flakes-like-surface-structure was generated after underwater treatments with two-step method. KrF laser treatments increased Sq and Sdr values. Sdr was more influential for adhesive joint shear strength. These laser treatments in all environments transformed secondary and tertiary aliphatic amines to primary and secondary aliphatic amines, respectively. SLSS study confirmed that the highest shear strength of 35.78 MPa which was 45% higher than the untreated joint, was achieved after underwater treatment. Normal atmosphere and argon environment treatments resulted in 31.74 and 31.95 MPa, respectively. Adhesive failure which occurred after argon environment treatments, reduced after normal atmosphere treatments. Underwater treatments resulted in cohesive failure and thin layer cohesive failure.