Microscopic damage of lightning-damaged CFRP revealed by O-PTIR and Raman spectroscopy

Carbon fiber-reinforced polymer (CFRP) composites are increasingly used in aircraft structures, but their microscopic damage evolution mechanisms under lightning strike remain insufficiently understood. In this study, an impulse current generator was used to simulate Component-A lightning current, and T700 carbon fiber/epoxy laminates were subjected to different peak current amplitudes of 10, 20, and 30 kA. Optical photothermal infrared spectroscopy (O-PTIR) and Raman spectroscopy were employed to analyze the structural changes in the epoxy matrix and carbon fibers within the damaged regions. The results show that, with increasing current amplitude, the ablated area expanded, and resin removal and fiber exposure became more pronounced. O-PTIR results indicate that the main characteristic peak positions in the 800–1800 cm -1 range remained nearly unchanged, while the peak intensities and spectral profiles varied with current amplitude and sampling position. This suggests that lightning strike mainly changes the degradation degree and relative abundance of existing resin functional groups, rather than generating new stable spectral peaks. Raman results show that the material still exhibited typical D and G bands of sp 2 carbon, and that the ID/IG ratio varied non-monotonically with current amplitude, indicating different degrees of structural disorder, carbonized residues, and possible thermally induced changes in sp 2 structural ordering on the carbon-fiber surface. The combined O-PTIR and Raman results indicate that resin degradation is the dominant microscopic response at low-to-moderate current levels, whereas severe resin ablation, fiber exposure, and carbon-structure disorder become more significant at higher current levels. This study provides spectroscopic evidence for understanding lightning-induced microscopic damage in CFRP and offers a reference for damage assessment of aircraft composite structures.