233 / 2018-09-23 21:22:42

A ReaxFF-Based Molecular Dynamics Simulation of Electro-thermal Cracking for Carbon Nanotubes/Epoxy Composites

Epoxy resin,carbon nanotube,electro-thermal cracking,micro-control,reactive molecular dynamics simulation

The aging and cracking epoxy resin is one of the important factors affecting the safe operation of DC GIL (Gas insulated metal-enclosed transmission line). The addition of a certain mass fraction of nanoparticles can effectively control its heat resistance. At present, the research on nanotube/epoxy composite medium focuses on experimental preparation and performance testing. But the analytical method based on experimental tests cannot monitor the cracking process in real time. In recent years, molecular simulation technology has become the third important scientific method to study the physical and chemical properties of materials in addition to experimental methods and theoretical methods. Four cross-linked epoxy resin models were established, including the pure epoxy resin model, and the uncapped, semi-capped and fully capped carbon nanotube/epoxy composite media models. Based on the reaction force field ReaxFF, the effects of van der Waals force and Coulomb force were incorporated. The molecular dynamics simulation of electro-thermal cracking was carried out on the four medium models using LAMMPS software. The effects of different temperatures and temperature rise rates on the cracking process and the final product were compared to select the simulated temperature, and the DC electric field was applied with reference to the actual operating conditions of the GIL insulator. For different kinds of medium models, the micro-control effects of carbon nanotubes on electro-thermal cracking of epoxy resin were analyzed. The initial cracking temperature, the number of molecules and the trend of the main cracking products of each system were counted, and compared with the experimental results. The regulation effect of carbon nanotubes on the heat resistance of epoxy resin was investigated. The results show that compared with the pure epoxy resin model, the initial cracking temperature of the carbon nanotube/epoxy composite medium models increase during the cracking process, which is consistent with the experimental results. As the simulation time prolonged, the number of molecules in the cracking gradually increase and eventually become saturated. The number of normalized molecules in the composite medium model after doping carbon nanotubes is reduced by about 15%. And the uncapped carbon nanotube/epoxy composite medium model has the least number of normalized molecules, and the semi-capped carbon nanotube/epoxy composite medium model is second. The main products of epoxy cracking are water H2O, hydrogen H2, methane CH4, formaldehyde CH2O and glyoxylic acid C2H2O, and a small amount of carbon monoxide CO and carbon dioxide CO2. The initial generation time and content change trend of small molecular products produced by the cracking of composite media are basically unchanged, but their numbers and types are reduced.
The addition of carbon nanotubes improves the elastic properties of the epoxy system at high temperatures, inhibits the movement of epoxy resin molecules, and effectively regulates the heat resistance of epoxy resin composite media. Finally, the thermal stability of the epoxy resin is improved to some extent, and the electro-thermal aging process is alleviated. Studies have shown that the effect of the uncapped and semi-capped carbon nanotube composite media models are more significant. The simulation can provide an auxiliary design means for the microscopic regulation of epoxy resin composite media.