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ISSN Печать: 2150-766X
ISSN Онлайн: 2150-7678
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EFFECT OF FE2O3 ON THE MATERIAL PROPERTIES OF AP/AL/HTPB BASED PROPELLANTS
Краткое описание
Catalytic quantities of Fe2O3 are frequently added to certain propellant formulations to facilitate the characteristic burn rate. Past studies have demonstrated that the addition of less than 2% Fe2O3 in Ammonium Perchlorate (AP) based propellants may result in a significant increase (60-70%) in the bum rate. The mechanistic interpretation for this increase is not well understood. Indeed, very little is known regarding the role Fe2O3 plays in the combustion process or what effect it's inclusion may have on the mechanical properties of this class of propellants. With this motivation a comprehensive study of both the combustion and dynamic properties of selected AP/A1/HTPB propellants was undertaken at NAWC. Initial measurements using the closed bomb technique indicate that the increase in bum rate is pressure dependent for these propellants and any catalytic effect due to Fe2O3 is lost above 0.3 Kbar. To address the safety issue of these propellants it is desirable to examine the material response due to dynamic loading and high strain-rate. These type experiments closely approximate the likely hazard scenarios which the energetic material may experience. For example, shock experiments are typified by large non-hydrostatic stresses and very rapid loading rate such as that imparted by fragment impact.
Three formulations differing only in coarse AP particle size and the addition of less than 1.2% of Fe2O3 formed the basis of this study. A total of twelve shock loading experiments were performed for input pressures to 200 Kbar (2.9×106 psi). Shock Hugoniot relationships for the three formulations were determined and compared to the Hugoniot for high density (≈94% TMD) AP. The experimental Hugoniots for the formulations without Fe2O3 were in good agreement with the AP Hugoniot. The formulation with Fe2O3 demonstrated a larger impedance than the PS1 and PS2 formulations. This latter result is consistent with the high strain-rate experiments performed on a Split Hopkinson Bar (SHB) in the compression mode. The yield and failure stress plotted as a function of strain-rate were consistently higher for the propellant with Fe2O3 . The experimental results thus demonstrate that the addition of a small amount of Fe2O3 can measurably affect the mechanical response of the propellant host material. Since the shock experiments attain pressures much greater than the closed bomb experiments, this result also suggests that a different mechanism may be affecting the mechanical response.