No abstract

Using multiphysics simulations and experiments, we demonstrate that dielectric breakdown due to electric charge accumulation can lead to sufficient 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 electric field ( E-field) development in the material is driven by the flexoelectric and piezoelectric responses of the polymer binder to mechanical loading. A two-step sequential multi-timescale and multi-physics framework for explicit microscale computational simulations of experiments is developed and used. First, the mechanically driven E-field development is analyzed using a fully coupled mechanical–electrostatic model over the microsecond timescale. Subsequently, the transient dielectric breakdown process is analyzed using a thermal–electrodynamic model over the nanosecond timescale. The temperature field resulting from the breakdown is analyzed 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 generated. Both experiments and analyses show that flexoelectricity plays a primary role and piezoelectricity plays a secondary role. In particular, the time to ignition and the time to pre-ignition reactions of poled films (possessing both piezoelectricity and flexoelectricity) are ∼10% shorter than those of unpoled films (possessing only flexoelectricity).

Solid propellants suffer from a lack of active burning rate control. Active control could be capable of throttling propellant gas generation rates in applications ranging from adaptable airbags or other gas generators to solid rocket motors. In this study, we have investigated the concept of altering the burning behavior of solid propellants via surface area modification in the form of an adjacent slot. The conditions for burning in an adjacent slot to occur are considered, and several theoretical relationships are developed and presented between pressure and slot width for the threshold condition for penetration. The derivations assumed several different threshold criteria. Most considered convective heat transfer and applied an ignition threshold, whereas one derivation examined the quenching of a flame propagating into a slot. The resulting expressions were then applied to existing literature data and contrasted. The results showed that the derived equations fit the literature data well with our equation from the flame quenching derivation having the highest average R squared value.

No abstract

No abstract