Femtosecond laser micromachining of carbon fiber-reinforced epoxy matrix composites

Unidirectional carbon fiber-reinforced epoxy matrix composites fabricated by compression die molding technique were exposed to femtosecond laser pulses of 1030 nm wavelength, 560 fs duration and a pulse repetition rate of 100 kHz. Laser tracks were engraved on the composite surface using pulse energy from 1 to 5 μJ both in the direction parallel and perpendicular to the fibers axis. The resulted morphology of the laser treated surface was investigated by field emission scanning electron microscopy (FESEM). The laser induced periodic surface structures (LIPSS) with an average periodicity of 195 ± 45 nm were observed on the carbon fiber surface while the epoxy matrix showed fine granular morphology. The surface topography of the laser tracks was quantitatively analyzed by 3D reconstruction of stereographic pairs of FESEM images recorded at two different inclinations of specimen with respect to the incident electron beam. The difference in ablation depth of fiber and epoxy was measured from stereographic images which showed a remarkable change in ablation depth of fiber and the matrix for pulse energy in the range 1–3 μJ and 4–5 μJ. The observations made in this study are expected to be useful for achieving improved bonding in composite structure repaired by adhesive joining.