Advanced characterization of thermal degradation mechanisms in carbon fibre-reinforced polymer composites under continuous wave laser irradiation

This study provides a detailed and comprehensive analysis of the effects of laser power and beam diameter on the thermal damage characteristics of carbon fibre-reinforced polymer (CFRP) composites, aiming to uncover the underlying damage mechanisms using advanced characterization techniques. Continuous wave laser irradiation was performed with beam diameters of 3.18 mm and 5.70 mm at varying power levels up to 365 W to evaluate the influence of laser parameters on CFRP damage. High-resolution thermal imaging captured temperature distributions on the CFRP surfaces, revealing complex interactions between laser parameters and resulting thermal damage. Quantitative ultrasonic C-scan imaging offered detailed insights into the extent and distribution of damage, elucidating the interplay between laser parameters and CFRP integrity. Results show that for the 3.18 mm beam diameter, perforation times significantly decreased from 46 s at 215 W to 7 s at 365 W. Simultaneously, the damaged area reduced from 1204 mm² (48.2 %) at 215 W to 372 mm² (14.9 %) at 365 W, indicating efficient material ablation. Conversely, for the 5.7 mm beam diameter, perforation times were considerably longer, ranging from 393 s at 215 W to 269 s at 365 W, while the damage area increased from 1299 mm² (52.0 %) to 1712 mm² (68.5 %), reflecting a broader heat-affected zone (HAZ) and more extensive thermal damage. Mass loss trends also varied, decreasing with higher power for the smaller beam diameter but increasing for the larger beam, highlighting contrasting ablation efficiencies and thermal effects. Micro-CT imaging revealed internal structural changes in the CFRP, confirming SEM observations that detailed surface morphology alterations under varying laser conditions. Infrared micro-spectroscopy beamline (IRM) analysis further uncovered chemical modifications and compositional changes induced by laser exposure, providing insights into degradation mechanisms and residual stresses within the composite matrix. These findings significantly enhance the understanding of thermal damage mechanisms in CFRP, offering valuable implications for aerospace and high-performance composite applications.