Polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polyimide (PI) are widely used in aerospace due to their excellent properties. Understanding their aging behavior is essential for long‐term performance in extreme environments. This study examines the effects of thermal oxidative aging (at 250°C over varying periods) under humid conditions on their chemical, structural, thermal, mechanical, and dielectric properties. In PEEK, aging led to solidification and crosslinking phenomenon which resulted in increased tensile strength and storage modulus, while elongation at break and tan δ decreased. Dielectric permittivity, polarization charge density, and leakage current also declined with aging, while AC breakdown strength increased by 1.6% in PEEK. PTFE exhibited surface oxidation, thermal degradation, and a decrease in storage modulus, with an increase in loss tangent. Breakdown strength slightly decreased, while dielectric loss and leakage current increased over aging time. PI underwent severe mechanical degradation, with tensile strength reduced by 54% and elongation by 16%, along with oxidation‐induced discoloration. Low‐mass polar molecules generated in PI during thermal degradation which contributed to the deterioration of its dielectric properties, lead to increased permittivity, polarization, leakage current, and a lower breakdown strength observed after aging. These findings provide insights into degradation mechanisms, aiding aerospace material selection for extreme environments.

Electrical equipment is always subjected to various of operating conduction and voltage waves which cause insulation failure on the surface of pressboard (PB). In this paper, pre-breakdown streamers of surface discharge on the interface of PB in vegetable oil based Fe₃O₄ nanofluids (NFs) were observed by the shadowgraph method under lightning impulse voltage. The images indicate that streamers of NFs impregnated PB show more branches than that of pure oil impregnated PB. The stopping length of streamers propagation is calculated by shadowgraph images for NFs and pure oil. Results suggest that the stopping length of NFs impregnated PB is shorter under the same extra voltage. Secondary reverse streamer is generated at the dissipation process by the reverse electric field, which is caused by residual space charge imparted by primary streamer. Results indicate that the Fe₃O₄ nanoparticles have reduced the length of secondary reverse streamer. The positive and negative lightning breakdown voltage of Fe₃O₄ NFs impregnated PB is increased by 24% and 12% at 50mm gap, respectively. In addition, nanoparticles have effectively changed the electric field distribution resulting in the alleviation of streamer concentrated along the parallel direction of PB, and increased the lightning impulse breakdown voltage.

The thermal reliability of high-voltage aerospace cables is increasingly important for hybrid-electric and all-electric aircraft; however, most thermal aging studies of perfluoroalkoxy alkane (PFA) have focused on isolated specimens and therefore do not establish how material-scale aging translates into the response of a complete cable structure. In this work, a PFA-insulated cable comprising the conductor, primary insulation, and outer jacket was subjected to cyclic thermal aging with a maximum temperature of 280 °C for nominal elapsed durations of up to 1000 h. Each 24 h cycle comprised approximately 1 h of heat-up and 7 h of nominal dwell at 280 °C, followed by natural cooling and recovery. Macroscopic, FTIR, DSC, XRD, TGA, TG–MS, SEM/EDS, contact angle, DMA, tensile, and three-point bending analyses were used to correlate aging of the individual PFA layers with cable-level behavior. The results indicate two dominant aging regimes over the investigated intervals. During the earlier 0–500 h interval, physical annealing and structural ordering predominated, producing increased crystalline organization, morphological densification, restricted molecular mobility, and initial mechanical stiffening. At the later 720–1000 h conditions, degradation-associated structural rearrangement or possible chemi-crystallization became increasingly evident, accompanied by localized morphological defects, partial recovery of molecular mobility, and progressive loss of ductility. The outer jacket exhibited more pronounced aging-related changes in several thermal, morphological, and mechanical responses than the primary insulation. At the cable level, aging was further manifested by axial shrink-back and changes in bending force, secant stiffness, bending work, and apparent structural bending rigidity. The mechanical end-of-life criterion was not reached under the investigated conditions. By linking aging of the individual PFA layers to the dimensional and mechanical response of the assembled cable, this work extends previous material-level PFA aging studies toward cable-scale durability assessment for future electrified aircraft wiring systems.