Multiple time scale simulations of hotspot development due to dielectric breakdown driven by piezo- and flexo-electricity in energetic materials

We demonstrate using multiphysics/multi-timescale simulations that dielectric breakdown due to electric charge accumulation can lead to hotspot development leading to the initiation of chemical reactions in P(VDF-TrFE)/nAl films comprising a poly(vinylidene fluoride-co-trifluoroethylene) binder and nano-aluminum particles. The development of electric field in the material is driven by flexoelectric and piezoelectric responses of the binder to mechanical loading which has a time scale of hundreds of microseconds. The breakdown process leading to hotspots has a time scale of nanoseconds. A two-step framework for explicit microscale simulations is used. First, the mechanically driven electric field is analyzed using a mechanical-electrostatic model. Next, the transient dielectric breakdown is analyzed using a thermal-electrodynamic model. The temperature field resulting from the breakdown is used to establish the hotspot conditions for the onset of self-sustained chemical reactions. The results demonstrate that temperatures well above the ignition temperatures can be attained. Flexoelectricity plays a primary role and piezoelectricity plays a secondary role. The time to reaction initiation and the time to ignition of the poled films are ~10% shorter than those of the unpoled films.