Mechanism of influence of different flight altitudes on insulation breakdown performance of ETFE aviation cables

By studying the breakdown performance of ethylene-tetrafluoroethylene (ETFE) copolymer under low pressure via molecular dynamics simulations, and verifying the simulation results through low-pressure breakdown experiments, the insulation failure mechanism of ETFE materials under low pressure can be revealed on an atomic scale. First, molecular dynamics simulations are performed on ETFE. As the flight altitude gradually increases from 0 km to 24 km, the simulated pressure decreases from 101.300 kPa to 2.951 kPa. Correspondingly, the intermolecular distance increases by 9.692%, the interchain interaction energy decreases by 8.383%, the free volume fraction of ETFE increases by 62.586%, and the density of ETFE decreases by 7.737%. Subsequently, based on the electromechanical breakdown theory, it is deduced that the breakdown field strength of ETFE decreases by 17.626%. Finally, the low-pressure breakdown experiment shows that the breakdown field strength decreases by 40.078%, and the density measurement test indicates that the density decreases by 1.574%. Both simulation and experimental results confirm that the breakdown field strength of ETFE decreases with the reduction of pressure. This is because under low-pressure conditions, the increase in free volume fraction and the decrease in density provide a longer mean free path for free electrons. And the decrease in charge trap level weakens the charge trapping capability, leading to a higher concentration of free electrons. All these factors contribute to the reduction of the breakdown field strength of ETFE. This study provides performance prediction and failure mechanism analysis for the application of ETFE in aerospace and high-altitude extreme environments, and has guiding significance for the optimal design of aerospace insulation ETFE materials.