Mechanism of Damage and Micro‐Characterisation of Irradiation‐Induced Free Radicals on the Epoxy Insulation of the Bridge Arm Reactors at High Altitude

ABSTRACT Damage degradation of epoxy resin insulating materials by free radicals triggered by the ultraviolet irradiation environment at high altitude has become a key issue that restricts the reliability of the bridge arm reactor at high altitude. The dynamic degradation mechanism of three types of distinctive free radicals, namely alkyl (CH 2 ), alkoxyl (CH 2 O) and peroxyl (CH 2 OO), on the epoxy resin cross‐linked network is systematically elucidated using the ReaxFF molecular dynamics simulation approach. The analysis of the study demonstrates that the radicals initiate main chain breaks by precipitating H ions or directly attacking the weak aliphatic bonds in the cross‐linked network. The degradation product results show H 2 O and H 2 small molecule products under all three radicals. Furthermore, it is also found that alkoxyl and peroxyl also induce CO generation, with the highest number of small molecule products under peroxyl. To quantitatively evaluate microscopic damage in ultraviolet (UV)‐aged epoxy resins, this study introduced cross‐linked structural integrity as an evaluation index. The integrity calculations indicate that peroxyl radicals, characterised by their dioxygen structure, induce the most severe degradation, ultimately reducing the cross‐linked structural integrity to as low as 56%. This finding provides a profoundly detailed understanding of the mechanism of chemical bond cleavage and degradation product formation during UV ageing of epoxy resins at the molecular level and identifies peroxyl as the primary inhibitory target for material stabilisation. Consequently, this study establishes a theoretical basis for the rational design of irradiation‐resistant epoxy resin modification, ultimately enhancing the operational stability of bridge‐arm reactors at high altitude.