Processing Characteristics of Gun Propellants

Using especially modified torque and capillary extrusion rheometers the rheological behaviour of a typical triple-base gun propellant has been examined as a function of such processing variables as temperature, solvent content, time taken to incorporate, filler content and filler shape. Propellant doughs flow according to the law \documentclass{article}\pagestyle{empty}\begin{document}$ \sigma -\sigma _0 = {\rm K}\dot \gamma ^{\rm n} $\end{document} where σ is the shear stress applied to the dough to maintain a shear rate of γ, σ₀ is the yield stress at which flow commences, K is the consistency index and n is the flow behaviour index. Variations in these constants as a function of the above mentioned variables are presented and their implications discussed. Resultant changes in the physical properties of the dried extruded propellant also are monitored.     

Burn Rate Models for Gun Propellants

In the past, Vieille's law and minor modifications of it described sufficiently the linear burning rate of gun propellants which governs the design of charges by interior ballistic simulations. Recent developments to increase the performance led to new gun concepts and innovative propellants. These are the electrothermal‐chemical gun, porous and foamed charges as well as formulations exhibiting a temperature independent burning. Vieille's law cannot fully meet experimental results in these cases. Approaches based on the heat flow equation in the solid energetic material give simplified formulas to extend the validity. These burning rate models have the ability to describe the experimentally determined burning behavior at least in a simplified or qualitative way. More sophisticated methods consider complex geometrical structures in the solid or take into account the actual progress in phase behavior and reaction kinetics of heterogeneous combustion. The dependence of the burning rate on initial temperature, on phase transitions, porous structure and gaseous reactions can be described.     

LOVA Gun Propellants with GAP Binder

First results will be presented in the field of LOVA gun propellants with polyglycidylazide-binder system. Theoretical calculations and experimental investigations were carried out to get informations about the ballistic behavior of this type of gun propellant. Chemical stability and mechanical properties were also determined. In addition, the bullet impact test was performed. All these dta were compared with those of nitramine-gun propellants based on HTPB.     

Burning Characteristics of Consolidated Gun Propellants

To improve the combustion behaviors of conventional consolidated propellants, consolidated propellants were prepared using porous propellant grains as fast‐burning filler. The porous propellant grains were prepared by supercritical fluid foaming process and exhibited the high burning rate. The multi‐perforated structure of the consolidated propellants was designed and adopted to obtain high burning progressivity. To investigate the burning characteristics of the consolidated propellants, closed vessel and quenched combustion experiments were carried out. The results show that deconsolidation of the consolidated propellants does not occur, and that the consolidated propellants exhibit high burning rates and high burning progressivities. Besides, the results show that the consolidated propellants burn steadily even at low (−40 °C) and high temperatures (50 °C).     

Impact Testing Methods for Gun Propellants

A tower-type drop-weight tester is used to characterize mechanical properties of LOVA gun propellants ata nominal strain rate of 300 s⁻¹. This study is a comparative evaluation of two testing methods, namely the original and the newly introduced one, that differ in the initial experimental setup. The results of the evaluation show that with the original testing method, the specimens are strained nonlineraly which, at times, has led to an anomalous compressibility reduction of the specimen. The newly introduced testing method improves the strain rate control and uniformity in addition of having a very good results-reproduction capability.     

发射药用聚氨酯热塑性弹性体的合成

针对新型发射药用热塑性弹性体的要求,分析和讨论了弹性体的分子设计原则,以能与硝酸酯互溶的聚乙二醇为软段,4,4'-二苯基甲烷二异氰酸酯和乙二醇为硬段,合成了一类热塑性聚氨酯弹性体(TPUE).用DSC、FTIR、DMA等分析技术对弹性体的结构和性能进行了表征.结果表明,在所选择的硬段含量范围内,合成的样品具有聚氨酯的特征结构(氨基甲酸酯基),且具有一定的微相分离结构,与分子结构设计基本一致.软段的玻璃化转变温度较低,具有一定的低温力学性能.     

Rapid Methods for Quality Control of Gun Propellants

Several single-base, double-base, and triple-base gun propellants were analyzed by three different methods:

• Conventional analytical methods (TL 1376–600)
• High-pressure liquid chromatography (HPLC)
• Derivative spectroscopy.

The results obtained by these methods agree well and show a good reproducibility. However, compared with each other, the chromatographic methods are not only more rapid and more flexible than the conventional wet chemical analysis, they enable a quantitative determination of blasting oil mixtures like nitroglycerin or diglycoldinitrate. The same holds for many other explosives, stabilizers and stabilizer reaction products.     

发射药抗冲击力学性能研究进展

综述了利用落锤法、摆锤法、数值仿真等方法研究发射药抗冲击力学性能的研究状况,并介绍了从发射药微观结构研究其力学性能的研究进展。     

发射药的热自燃实验研究

进行了堆积直径为 2 0 0～ 30 0 mm的发射药的热自燃实验 ,并与直径 37～ 85mm的实验结果进行了比较。说明在热自燃条件研究中 ,大型验证实验是必不可少的     

Burning of Nano-Aluminized Composite Rocket Propellants

Several aluminum nanopowders were examined and compared with the final goal to evaluate their application in solid rocket propulsion. A detailed investigation of pre-burning properties by the Brunauer-Emmet-Teller method, electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy was carried out. Ballistic properties and the combustion mechanism of several aluminized propellant formulations were investigated. In particular, aggregation and agglomeration of metal particles at and near the burning surface were analyzed by high-speed high-resolution color digital video recordings. All tested nano-powders are of Russian production; their physical characterization was carried out at the Istituto Donegani (Novara, Italy); ballistic studies were performed at the Solid Propulsion Laboratory (Milano, Italy) using laboratory and, for comparison, industrial composite propellants based on ammonium perchlorate as an oxidizer. Results obtained under a fair variety of operating conditions typical of rocket propulsion indicate, for increasing nano-Al mass fraction or decreasing nano-Al size, larger steady burning rates with essentially the same pressure sensitivity. While aggregation and agglomeration phenomena still occur, their significance may be reduced by using nano-Al instead of micro-Al. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 80–94, November–December, 2005.     

Thermal Decomposition of RDX Composite Propellants

The thermal decomposition characteristics of RDX, binders, and RDX composite propellants were studied using thermal analytical techniques. Three kinds of binders were tested to elucidate the role of binder on the burning rate of the propellants. There were no apparent correlations between the thermal decomposition rates of binders and the burning rates of propellants, whereas there was a correlation between the decomposition temperature and the burning rate of the propellants. It is found that the major factor which controls the burning rate is the initial thermal-decomposition stage of the binders. Thus, the burning rate of nitramine composite propellants appeared to be largely dependent on the physical and chemical properties of binder.     

Burning Rates and Thermal Behavior of Bistetrazole Containing Gun Propellants

The influence of two selected bistetrazoles, 5,5′‐bis(1H‐tetrazolyl)‐amine (BTA) and 5,5′‐hydrazinebistetrazole (HBT), on the combustion behavior of a typical triple‐base propellant was investigated. Seven propellant formulations, one reference and six others incorporating 5 %, 15 %, and 25 % of either HBT or BTA compounds, respectively, were mixed and extruded into a cylindrical, no perforations, geometry. The resulting propellants showed high burning rates, up to 93 % higher than the reference formulation at 100 MPa. However, the increase in burning rates came at the cost of higher burning rate dependency on pressure, with a pressure exponent as high as 1.4 for certain formulations. HBT‐containing propellants showed notably lower flame temperature when compared to the reference formulation, with a flame temperature reduction of up to 461 K for the propellant containing 25 % HBT. The thermal behavior of the propellants was also investigated through DSC experiments. The addition of bistetrazoles provided lower decomposition temperatures than the pure nitrogen‐rich materials, indicating that the two compounds probably react readily with the −ONO₂ groups present in the nitrocellulose and the plasticizers used in the formulation. The onset temperature of all propellants remained within acceptable ranges despite the observed decrease caused by the addition of the bistetrazole compounds.     

The Quantity/Distance Category of Gun and Rocket Propellants

The quantity/distance categorisation of explosive materials is discussed. The procedure for the standard UK laboratory-type test (large sealed vessel test) is described. The borderline, in terms of the test, between fire and explosive risks has been established by testing materials for which the nature of the hazard is previously known. Trials have established that boxed UK plastic (composite) propellants are fire risks only.     

发射药燃烧转爆轰的试验研究

为研究发射药燃烧转爆轰特性及其影响因素,采用联合国危险分级试验中燃烧转爆轰试验方法对单、双、三基以及不同药型的发射药进行燃烧转爆轰试验。结果表明,在管厚4mm弱约束条件下,只有三基小粒发射药发生爆轰,在管厚9mm强约束条件下,6/7双基药、6/7叠氮发射药、6/7三基药以及三基小粒药发生爆轰。发射药配方中添加硝化甘油(NG)、叠氮硝胺(DA)和黑索金(RDX)以及减小药型尺寸,可增强发射药的燃烧转爆轰能力,同时,提高壳体约束强度更易发生燃烧转爆轰。     

Some Experiments on Model Composite Solid Propellants

Experiments on two-dimensional model propellants using cylindrical oxidizer (ammonium perchlorate) pellets in a fuel matrix (CTPB) are described. Measurements show that burning rate of AP in the fuel environment is lower than of pure AP. The oxidizer-to-fuel ratio seems to be fuel-rich when the oxidizer particles are imbedded in contact with the fuel and it becomes oxidizer-rich for a non-zero separation between oxidizer particle and the fuel.     

Impact Sensitivity of Azide Polymer Composite Propellants

Effects of azide polymers on the sensitivities and fragmentation mechanism were studied in this paper. Only fragmentation was observed at lower impact velocity, up to 172 m/s, even with an one-kilogram impactor. Most of the propellants showed linear relationship between an impact velocity and a fragmented fraction. The critical impact velocity, V_CR, depended on the amount of the binder but not on the chemical structures. The propellants which had no particle oxidizers showed high V_CR and their cracks were hard to grow into a piece of fragment. Nitramine-binder matrix dewetting caused by the deformation of the propellant was supposed to terminate the crack propagation and to damp the impact energy at a higher impact velocity. In AP-based propellants impact velocity dominated the initiation mechanism and impact energy did not control the ranking of the reaction. The friction energy played a more important role in the initiation than did the impact energy. There was no difference in the sensitivity to the card gap test between the azide polymer and HTPB binder.     

Gun Propulsion Concepts. Part II: Solid and Liquid Propellants

The present paper deals with both the conventional solid propellant and modern liquid propellant gun concepts. Solid propellant guns, known since the 14th century, are still being investigated, although this concept represents a relative mature technology. Thus any progress is predominantly a refinement of existing techniques. Comparatively, liquid propellant gun research and development address a rather new technique and invoke some improvements over conventional solid propellant systems. Especially, automatic system are easier to design, artillery zoning is more easily achieved, cartridge disposal is avoided, and high-energetic liquid propellants or special system designs offer higher performance. Therefore, the liquid propellant gun technology seems to be a near-term technology that, complementary to solid propellant gun concepts, might play a role in future armament.     

Investigation of Liquid Gun Propellants: Electrical ignition of LGP 1846

Progress achieved in the study of the electrical ignition of the hydroxylammonium nitrate(HAN)-based liquid gun propellant LGP 1846 is described. The goal of the work is to develop an igniter system suitable for regenerative liquid propellant guns. Several igniter configurations of the one- as well as the two-stage types designed by the Ballistic Research Laboratory and the Fraunhofer-Institut EMI-AFB, have been tested. Voltage and current as well as the pressure histories were recorded. Calculations of electrostatic field distributions discussed here were obtained by a finite element code implemented at Dynamit Nobel. The theoretical analysis yielded alternative electrode designs for future testing. In addition, a specially designed igniter chamber equipped with sapphire windows was used at EMJ-AFB to study the fundamentals of the electrical discharge by means of high-speed photography.     

Combustion Wave Structure of AP Composite Propellants

The combustion mechanism of ammonium perchlorate (AP) composite propellants were studied. The oxidizer-rich propellants tested were made with excess concentrations of AP particles. The pressure deflagration limit of propellant decreases with increasing the concentration of binder. The combustion wave consists of two reaction regions I and II: the region I is the zone of AP monopropellant flame and the region II is the zone of diffusion flame. The heat flux feedback from the gas phase to the burning surface increases as pressure increases, and the heat flux is responsible for the burning rate characteristics.