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Dimitrios N. Gkritzapis^a, Elias E. Panagiotopoulos^b, Dionissios P. Margaris^b and Dimitrios G. Papanikas^b
((a) Athens, Greece, GR 11522; (b) Fluid Mechanics Laboratory, Mechanical Engineering and Aeronautics Department, University of Patras, Patras, Greece, GR 26500)

Abstract: A full six degrees of freedom (6-DOF) simulation flight dynamics model is applied for the accurate prediction of short and long range trajectories of high and low spin-stabilized projectiles and small bullets via atmospheric flight to final impact point. The projectile is assumed to be both rigid (non-flexible), and rotationally symmetric about its spin axis launched at low and high pitch angles. The projectile maneuvering motion depends on the most significant forces and moment variations, in addition to wind and gravity. The computational flight analysis takes into consideration the Mach number and total angle of attack effects by means of the variable aerodynamic coefficients. For the purposes of the present work, linear interpolation has been applied taking data from official a tabulated database. The aforementioned variable flight model is compared with a trajectory atmospheric motion based on appropriate constant mean values of the aerodynamic projectile coefficients. Static stability, also called gyroscopic stability, is examined as a necessary condition for stable flight motion in order to determine the sufficient initial spinning projectile rotation. The efficiency of the method developed gives satisfactory results compared with published data of verified experiments and computational codes on atmospheric dynamics model flight analysis.

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Abstract: A full six degrees of freedom (6-DOF) simulation flight dynamics model is applied for the accurate prediction of short and long range trajectories of high and low spin-stabilized projectiles and small bullets via atmospheric flight to final impact point. The projectile is assumed to be both rigid (nonflexible) and rotationally symmetric about its spin axis launched at low and high pitch angles. The projectile maneuvering motion depends on the most significant forces and moments, in addition to wind, gravity and Magnus effects. The computational flight analysis is based on appropriate constant mean values of the aerodynamic projectile coefficients taken from an official tabulated database. The newer ICAO atmospheric model simulates the height distributions of density, pressure and temperature properties of the air. Static stability, also called gyroscopic stability, is examined as a necessary condition for stable flight motion in order to determine the sufficient initial spinning projectile rotation. The efficiency of the method developed gives satisfactory results compared with published data of verified experiments and computational codes on atmospheric dynamics model flight analysis.

Keywords: trajectory dynamics simulation, constant aerodynamic analysis, high and low pitch angles, Magnus effects, symmetric projectiles, static stability criteria

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Abstract: Ignition and combustion properties of aluminum powder up to 250 kbar pressure were successfully determined. Hydrodynamic modeling combined with parameterized reaction profiles was used to match the experimental metal plate profiles to calculated values and the metal reactivity was determined from the parameters thus obtained. The reaction profiles over a wide range of specific volumes and pressures were obtained.

Aluminum ignited only if the detonation temperature was higher than 2300 K and the aluminum oxide was decomposed; even a strong shock wave was not able to clean the aluminum surface to promote ignition at lower temperatures. Aluminum reactivity at the Chapman–Jouguet plane (C-J plane) was concluded to be insignificant in all cases studied. A maximum of only 17% reactivity by an expansion ratio of 1 : 50 was reached. The aluminum combustion could be best described with a power law Apn and the pressure exponent of aluminum was found to be slightly positive: +0.33. Nitrogen rich explosives were concluded to be necessary to convert Al energy effectively to mechanical work and to unambiguously measure the Al reactivity.

Keywords: aluminum, Chapman–Jouguet plane, ignition, combustion, hydrodynamic modeling

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Abstract: Composite propellants contain binder as fuel which connects oxidizer particles and metals. The burning rate of a propellant is affected by the concentration and type of binder. Pyrolant is mixed with oxidizer particles and metal particles. Pyrolant does not contain binder, so burns smoothly. The burning rate of black powder (BP) which is a kind of pyrolant is higher than that of AP composite propellant. The shorter the reaction time in the gas phase near the burning surface of black powder becomes, the higher the burning rate becomes. The burning rate of BP is inversely proportional to the ignition delay time.

Keywords: Black Powder, pyrolant, ignition delay time, burning rate

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Abstract: An experimental study of laser ignition of Zr/KClO₄, Zr/PbCrO₄, Fe/KClO₄, Fe/KNO₃, B/KClO₄ and B/KNO₃ mixtures is presented in this paper. The ignition system is composed of two lenses which focus the laser beam on the tablet. A sapphire porthole, juxtaposed with the pyrotechnic composition, protects the optical unit but causes losses of heat which result in an increase of the energy threshold.

This experimental set-up was used to determine the ignition sensitivity of five mixtures. A particular behaviour of B/KNO₃ was observed. Experimental results pointed out an increase of the energy of ignition when the laser power grows. The other mixtures exhibit a conventional behaviour of the trend of ignition threshold E₅₀ according to the power P of the laser beam: a continuous decrease of the value of E₅₀ is observed when P is rising.

Some parameters linked to the experimental device also have a great influence. Among them the power density seems to be predominant but the thermal conductivity of the sapphire windows also plays an important role. It is possible to find an optimum value of the laser diameter, for a given power density. This experimental and parametric study have shown that, on such devices, it is possible to find optimal conditions of the ignition of various pyrotechnic mixtures.

A modelling, based on a progressive absorption of the laser beam inside a reactive pyrotechnic composition, was developed. It takes account of the energy exchanges between the ignition system and the pellet. Two interface parameters make it possible to optimize calculations. One relates to the heat transfer on the level of the porthole/tablet interface, the other relates to the laser absorption of energetic materials. By combining these two terms, it has been possible to corroborate the experimental thresholds on five different pyrotechnic mixtures.

To evaluate the interface parameters, whose implication in initiation is critical, several methods are exposed. One of them proposes a numerical calculation based on a random and automatic installation of the grains. The result gives Gaussian variables. This method enables simulation of the statistical tests of Bruceton and Langlie which are used in pyrotechnics.

The numerical results show that the sensitivity of the mixtures depends primarily on the propagation of heat towards the porthole and the interior of the tablet, as well as on the in-depth absorption of the laser in the pellet.

Keywords: laser diode, ignition, pyrotechnic mixtures, numerical modeling

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Abstract: In this paper, we report the elaboration and the characterization of several kinds of nanothermites made at the French German Research Institute of Saint-Louis (ISL). Three types of materials are presented herein: tungsten trioxide based nanothermites obtained by physical mixing of this metallic oxide with aluminum nanoparticles; tungsten trioxide based nanothermites elaborated by coating WO₃ nanoparticles with aluminum using a chemical process; and molybdenum oxide based nanothermites composed of Al_xMo_yO_z nanostructured phases and aluminum nanoparticles. In the light of these examples, we have identified general trends concerning the structural and reactive behavior of the new materials.

Keywords: nanothermites, tungsten oxide, molybdenum oxide, aluminum coating

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Abstract: HNF, hydrazinium nitroformate, H₃NNH₂⁺•C(NO₂)₃^–, is a water soluble salt. It has a positive oxygen balance of 13%, a much more positive enthalpy of formation than ammonium perchlorate (AP) and a much higher heat of explosion than AP, 5579 J g^–1 against 1972 J g^–1. Additionally it has no chlorine and all the problems with hydrogen chloride formation can be avoided when used as oxidizer in rocket propellant formulations. All these advantages together could make HNF an oxidizer with better performance than AP. One inherent disadvantage may be the lesser thermal stability of HNF. Therefore an extensive investigation was performed on the thermo-chemical stability of HNF. Three sample lots of HNF have been investigated at ICT. They were provided by APP BV, The Netherlands. The thermal stability was determined by the following methods:

• autoignition temperature with 0.2 g at 5 °C min^–1 heat rate in a Wood’s metal bath
• vacuum stability test (VST)
• heat generation rate as function of time and temperature
• mass loss as function of time and temperature
• adiabatic self heat rate

Lots 2 and 3 have been characterised by heat generation rate at 60, 65, 70 and 75 °C and in short by mass loss. Lot 1 was extensively used for mass loss determinations in the temperature range 50 to 80 °C. HNF shows high heat generation rates. All curves from both methods indicate self accelerating behaviour. They have been described with autocatalytic reaction kinetic models. The Arrhenius parameters have been determined for lot 1 from mass loss data and for lots 2 and 3 from heat generation data. The activation energies for the intrinsic decomposition reaction are 166, 139 and 132 kJ mol^–1 and for the autocatalytic reaction 159, 128 and 117 kJ mol^–1 in the order lots 1, 2, 3. The kinetic data are compared and discussed. Data for lifetime at different temperatures are given in terms of the times to reach preset values of mass loss and energy loss.

Keywords: autocatalytic, kinetic, HNF

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