Etching of long fiber polymeric composite materials by nanosecond laser induced water breakdown plasma

Composite materials are widely used in industry due to their superior material properties and light weight. However, shear failure can occur at the interface between the fibers and polymer matrix when a tensile force stretches the matrix more than the fibers. Repairing the damaged composite material appears to be cost effective but still remains a challenge despite extensive research. Laser induced water breakdown plasma, which is generated by the strong interaction between nanosecond laser and water, is proposed in this work to etch the surface layer of a carbon fiber reinforced composite sample. It is found that the polymer layer can be effectively removed by the plasma while the carbon fiber remains almost intact. The dependence of the etching depth on the laser power density, laser focus position, and the number of shots are also investigated in this work. The maximum possible etching depth is around 350 μm with 50 laser shots at laser power density of 70 GW/cm2.