High speed mechanical characterization and temperature constraints of propellants with energetic binders

Abstract

One of the most promising areas of improvement of the solid propellant technology is to substitute the HTPB with energetic binders. This allows to increase significantly the specific impulse leading to high performance and/or low polluting propellants, with systems able to reduce chlorine . The main problem for the development of formulations with energetic polymers seems to be the assessment of the mechanical properties in reference to the performance obtained with HTPB. The mechanical behaviour is conventionally determined by Master Curves of the properties in function of log(RaT), according to the TTEP principle. For propellants showing critical Tg, a significant range of induced stresses can be more conveniently achieved by high strain rate rather than using low temperatures processed by W.L.F. equation. This study has been fulfilled in Fiat Avio for optimizing some formulations of advanced propellants with GAP and PNIMMO as binders. The results experimentally demonstrated the TTEP principle also about the Tg and showed the quasi-glassy stiffness of these propellants when stressed at high cross-head rates at T>Tg, due to the time-dependence of the viscoelastic characteristics of their matrix. A new route to mechanically evaluate the solid propellants has been indeed approached, reproducing the real stresses arising form the motor modeling, with benefits in the economical and time concerns for developing conventional and advanced propellants.