Refining the technique
TWI selected a nanosecond pulsed Nd:YAG laser to provide energetic treatment of PEEK surfaces, to investigate its effectiveness in increasing the performance of lap shear adhesive joints. The laser was used to irradiate the PEEK, by rastering a spot of ~1mm diameter across a large area.
The resulting surfaces were characterised using single-lap shear testing and advanced surface analysis techniques. Single-lap shear testing of PEEK joints showed that the strength of adhesively bonded joints is greatly improved by laser treatment – up to 13 times that of untreated PEEK. The higher laser power intensities (≥107 W mm-2) disrupted the surface of the PEEK more than the lower laser powers intensities (<107 W mm-2).
The derived surface free energy increased alongside laser power intensity. High-resolution surface chemical analysis showed that laser treatment only affects the near-surface at the extremity of the 1–2µm sampling depth. The process creates oxygen-containing functional groups at the surface.