Micromechanics analysis of carbon fiber/epoxy microdroplet composite under UV light irradiation by micro‐Raman spectroscopy

Abstract Evaluation of the surface morphology, chemical groups, interfacial microstructure, and mechanical properties of carbon fiber/epoxy resin microdroplet composites during ultraviolet photodegradation was carried out. The axial stress distribution and interfacial shear stress (ISS) distribution of the carbon fiber/microdroplet composite at 0.25% and 0.62% strains with different UV irradiation times were obtained using micro‐Raman spectroscopy. The results showed that after 40 hours of UV irradiation, tiny particles appeared on the surface of the carbon fiber/microdroplet sample, and with prolonged irradiation, the tiny particles grew larger and more in number. Benzyl methyl ketone was observed after 40 hours of UV irradiation, and the formation of the quinone methide structure, which causes the discoloration of composite, appeared after 300 hours of UV irradiation, and the tiny particles formed on the composite might be benzyl methyl ketone. The maximum axial stress reduced to 53% and 37%, and maximum shear stress reduced to 67% and 66%, for the 0.25% and 0.62% strain samples, respectively, when the UV irradiation time was extended to 940 hours. A power‐law function of ISS with irradiation times was proposed and is represented by τ_0.25 = 66.78 ‑ 8.296 × 10^–6 t^2.26 and τ_0.62 = 81.24 ‑ 2.20 × 10^–6 t^2.49. It was further determined that the loss of mechanical properties was slow during the first 300 hours of UV irradiation. This work provides a new approach for studying the influence of UV irradiation on the interfacial properties of fiber/polymer composite.