Epoxy and epoxide composites have a wide range of outdoor applications wherein they are affected by ageing. In this study, epoxy casting plates and epoxy-based composite rods for use in overhead conductors were prepared. A concurrent investigation concerning the ageing of epoxy resins and their carbon fibre composites was carried out via artificially accelerated experiments under hygrothermal and salt mist conditions. The moisture penetration along the depth, water absorption, appearance, hardness, density of the epoxy resins, and variation patterns of the impact strength and tensile strength of the epoxy-based composites were investigated. The ageing mechanisms were explored using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Both ageing modes had essentially similar influences on the properties of the resins and their composites; moreover, they did not significantly affect the chemical structure and microstructure of the epoxy resin, with the physical adsorption of water primarily observed during the ageing process. The moisture absorption behaviour of the epoxy obeyed Fick’s law. Although the water penetration rate in the salt mist ageing mode was slightly higher than that in the hygrothermal ageing mode during the early ageing stage, it was essentially the same during the later stage. The final moisture absorption rate at saturation was approximately 1.1% under both modes. The flexural strengths and impact strengths of the composites in both ageing modes followed a similar trend. They decreased gradually with the ageing time and then stabilized at almost the same value. The flexural strength was reduced from 803 MPa to 760 MPa and the impact strength from 383 J/m² to 310 J/m², indicating a decrease of approximately 5.4% and 19%, respectively. The absorbed water during the ageing process caused micro-cracks at the interface between the fibres and resin, weakening the interfacial strength and reducing the mechanical properties of the composites.

Polymer matrix composites (PMCs) often undergo aging as a result of ultraviolet (UV) radiation, which significantly impacts their performance and durability. This paper investigated the alterations in the microstructure and macroscopic properties of epoxy resin and its composite used in overhead wires during UV aging. Furthermore, the mechanism of UV aging for both resin and composite was revealed. The results showed that UV aging predominantly affected the properties of the surface layer resin. UV aging can induce molecular chain scission, which leads to resin weight change, color deepening, microcrack formation, a decline in mechanical properties, and other performance degradation behaviors under the combined action of many factors. With the increase in aging time, the weight change rate and hardness of the resin increased first and then decreased, while the mechanical properties of the composite decreased rapidly first and gradually tended to be constant. The bending strength and impact strength of the composite decreased by 6.0% and 12.8%, respectively, compared with the initial values. The purpose of this study is to comprehensively understand the UV aging behaviors of epoxy resins and their composites employed in overhead wires, and it also provides essential data for advancing the utilization and durability of epoxy resins and composites across aerospace, marine, and other outdoor applications.