فصلنامه مواد پر انرژی
سال هشتم شماره 1 (پیاپی 18، بهار 1392)

A two-dimensional numerical simulation is performed in the present work to study the structure of a detonation wave in high activation energy mixtures, which are characterized by their turbulent reaction zone structure and unreacted pockets. The process of transverse wave and triple point collision with the channel walls, formation and consumption mechanism of unburnt gas pockets is examined using very high-resolution numerical simulation. Results show that as the triple point collides with the channel wall, the transverse shock interacts with the unreacted pocket. After reflection of the triple point off the wall, the transverse wave interacts with the wall. During the collision and reflection process, the shear layer detaches from the shock front, producing a pocket of unburnt gas. Energy resealed via consumption of unburnt pockets by turbulent mixing due to hydrodynamic instabilities (Richtmyer-Meshkovnad Kelvin-Helmholtz instabilities) found to have profound role in re-initiation mechanism of detonations at the end of a detonation cell.

In this study, the effect of additives such as ammonium oxalate (AO), mixture of ammonium oxalate and strontium carbonate (SC) on AP/HTPB based composite propellants was investigated by burning rate, DTA, density and autoignition temperature measurements. The results show that the burning rates of these propellants are decreased significantly. DTA and autoignition temperature experiments results indicate respectively that the decomposition and autoignition temperatures of AP with these additives are increased. The burning rate temperature sensitivity of AP/HTPB based propellants is reduced significantly by the addition of AO or AO/SC, but the effect of AO is less than that of AO/SC. The reduced heat released at the burning surface of AP/HTPB/AO is responsible for the reduced temperature sensitivity. Synergetic effect between AO and SC at AP/HTPB/SC/AO based propellants causes the reduction of heat release and augmentation of the burning surface temperature. Thus, the burning rate temperature sensitivity is reduced. The results of this research in comparison with other results showed that the temperature sensitivity of the propellant formulation with 4% AO was lowered up to 4.8%.

In this paper, production of a double base propellant grains embedded with continuous metal wires by the screw extruder is investigated. The factors effecting the burning rate of the grains are analyzed and selection of suitable metal wires are discussed. Also, manufactured propellants with embedded metal copper, brass and steel wires (diameter=0.25 mm) were tested by Crawford Bomb method. By this process, the continuous metal wires embedded in grain are made straight and arranged properly to meet the design demands. The results showed that axial burning rate of the end-burning grain embedded with one continuous metal wires of 0.25mm diameter is 3.9 times as great as that of the propellant matrix. Also the torsion and rupture in the grains don’t occurred using embedded metal wire.

The JPX rocket fuel is a mixture of unsymmetrical dimethyl hydrazine and a nearly light hydrocarbon fuel. Regarding the presence of unsymmetrical dimethyl hydrazine and olefin compounds in the JPX fuel, emission of its vapors during fuel charging can be hazardous. On the other hand, after fuel charging, the internal surface of pipeline and related equipment is wetted with the liquid fuel. This fuel is hazardous from safety and environmental viewpoint and it is necessary to neutralize the vapors and wash the related equipment with an appropriate solvent. Aqueous solution of ethanol (5%) was selected for the equipment washing. Various oxidants were also compared for vapor neutralization and potassium permanganate was selected. Results showed that the oxidation reaction consists of two steps: in the first step, the potassium permanganate is reduced to manganese dioxide and in the second step, manganese dioxide is reduced to Mn(II) ion. The molar ratio of potassium permanganate to dimethyl hydrazine was found to be 0.506. Assuming the second order reaction with respect to dimethyl hydrazine, the rate constant was determined to be 6.1lit.mol-1min-1 at 25°C. The main products of the oxidation reaction included formaldehyde dimethyl hydrazone, dimethyl amine, ammonia, and water.

Penetration into concrete and concrete-steel targets is of prime importance to defense and civil industry scientists. Due to complexity of penetration process, the majority of the conducted studies in the related field have been experimental. In this study, the penetration depth of a long rod projectile into concrete targets is investigated by adjusting Alekseeveskiis-Tate analytical model, which has already been introduced for concrete targets. Since using this analytical model is required to have the dynamic resistance of the target, an analytical relation between dynamic resistance and compressive strength of concrete is developed. Considering the extended model for multilayer targets, penetration depth of long rod in non-homogenous multilayer steel-concrete targets is calculated. Numerical analysis using LS-DYNA suggested a very good agreement between analytical solution and experimental results.

The HNIW with the chemical name 2,4,6,8,10,12-hexanitro 2,4,6,8,10,12- hexaazaisowurtzitane (more commonly known as CL-20) and with cage structure is the most powerful non-nuclear explosive materials. CL-20 can exist as four different polymorphic phases (α, β, γ and ε) at ambient temperature and atmospheric pressure having different density and sensitivity. ε morphology, with more density is less sensitive and more appropriate for military applications. In this paper, both the synthesis and crystallization methods for the preparation of ε-CL-20 is investigated and the effects of different parameters (solvent, temperature, and stirring rate) on the particle size of ε-CL-20 prepared from crystallization method were studied. It is shown that the best solvent for crystallization of ε-CL-20 is ethyl acetate. Heptane and chloroform are more convenient as antisolvents. ε-CL-20 was analyzed by different techniques as Raman and FTIR, SEM and XRD.

Two effective quasi – static models are presented to consider pre and post- failure behaviors of the clamped circular plates subjected impulsive loads based on upper bound limit analyses of deformation. In first model, final profile is considered to have a conical shape, which is represented by radial and vertical motions of a single peripheral plastic hinge; permanent deflection is calculated before local failure. In second model, supposing the final deformation being as a dome shape, mechanism of deformation is caused by multi- peripheral stationary hinges with uniform or non- uniform distribution. In this part, motion after severance of the plate is considered at the instance that the local failure is occurred. Calculating plastic deformation energies, permanent deflection before the severance is computed and influence of number and distribution of hinges are investigated. Since, value of residual velocity after tearing can perform principal role for validation of a quasi static estimation of the deformation at transit threshold from the first failure mode into second one. So, having amounts of relevant energies, value of this velocity is evaluated without needing dynamic analysis. Finally, by comparisons between obtained results from introduced models and other works and experimental data, good agreements are observed.