Enhancement of fiber-matrix adhesion by laser ablation-induced surface microcorrugation

Micrometer-sized surface corrugations produced on Kevlar fiber surfaces by laser ablation were found to dramatically enhance the mechanical adhesion between the fibers and the epoxy matrix in a fiber-reinforced composite. Symmetric and asymmetric corrugation structures were produced by irradiating the fibers with high-fluence UV laser pulses at various incidence angles. The interfacial shear strength (IFSS) between the fibers and the matrix was measured using the microbond fiber-pullout method. Upon laser ablation treatment, the IFSS increased by 120% with symmetric corrugation profiles obtained with laser irradiation normal to the fiber axis, and 5-fold with asymmetric corrugation profiles obtained with the laser incidence angle at 45 degrees to the fiber axis. A similar enhancement was observed in pullout tests under wet conditions. A simple model based on an elementary analysis of the expected strain field in the presence of interface corrugation is found to provide a quantitative explanation of the observed strength enhancement factors.