فصلنامه مواد پر انرژی
سال پنجم شماره 2 (پیاپی 10، پاییز و زمستان 1389)

Aluminum nanoparticles are widely used in various energetic materials, such as pyrotechnics, explosives and propellants.In this research, the thermal behavior of aluminum nanoparticles (prepared by inert gas condensation process) and aluminum microparticles is investigated. The synthesis particles were characterized using Scanning Electron Microscopy (SEM), Particle Size Analysis (PSA) and X-Ray Diffraction (XRD) methods. The oxidation temperatures of aluminum nano- and micro-particles were determined as 490 °C and 550 °C respectively using Differential Thermal Analysis (DTA) method. It was also found that released heat due to oxidation reaction of the aluminum nanoparticles is higher than aluminum microparticles.

In this work, the effects of quality and quantity of three stabilizers as AkarditeII, 2-NDPA and CentraliteI on the heat of explosion and stability of double-based is investigated The results showed that, by increasing the amount of AkarditeII and 2-NDPA increased stability of propellant and decreased heat of explosion. By replace AkarditeII and 2NDPA with CentraliteI and AkarditeII mixture in the propellant heat of explosion of the DBP increased. Substitution of AkarditeII, with mixture of centraliteI and AkarditeII, caused higher stability but 2-NDPA doesn’t affect these properties.

In this research, internal ballistics of solid rocket motor (SRM) has been simulated numerically including two phase flow phenomena. The flow field is consisting of combustion chamber, cylindrical grain, and converging-diverging conic nozzle. One-dimensional transient Euler equations has been solved through Jameson method. The mentioned equations are discretized using fourth order Runge-Kutta integration, and spatial discretization resulted to a central difference scheme. The effect of erosive burning, propellant type, two phase flow, and particle diameter are considered. It is seen that pressure is increased at starting of the motor because of erosive burning. Two phase flow decrease efficiency of the motor, and decrease total and specific impulse by changing propellant type from composite two double bases. The results are compared with other references for validation.

Explosive welding is a solid state process in which bond is produced by a high oblique impact of two plates with the controlled explosive charge. In this paper, the explosive welding of Ms90 brass flyer plate with the St14 steel base plate are considered by using the parallel set up geometry. From the practical viewpoint, various parameters such the stand-off distance, dynamic angle, type and amount of charge, etc. influence the quality of the welds. However, all of these parameters can be summarized as the parameters of dynamic angle and welding speed. There is a region in this diagram, known as welding window, which determines the acceptable bonding region. The welding window is important in determining the optimum welding parameters before performing any practical application reducing the time and cost. In this contribution, the welding window of Ms 90 brass and St 14 steel is drawn using the existent equations and the shapes of the interface of the various tests were analyzed by optical microscope. The micrographs show that the shape of the interface changes from straight to wavy interface and the grains located close to the interface are elongated along the explosive direction. Grains are more elongated along the explosive direction with the explosive charge. The depth of interface microstructure increases with the explosive charge. In this study, the simulation of explosive welding process was carried using the ABAQUS finite element software and the pressure distributions at the collision zones were obtained for all experiments.

Many concrete structures may be exposed to high rate dynamic loadings like impacts, explosions, etc. Thus, it is necessary to know the behavior of this material in order to predict the response of the structure. Understanding the response of concrete at high strain rates is a main factor both for a successful design of protective structures and reducing the damage of constructions. As the concrete is exposed to dynamic loading, its behavior depends on the strain rate. Therefore, an appropriate model is needed to present the theoretical characteristic of concrete correctly. The purpose of this paper is to present an approach used to couple the viscoplastic model with the damage theory. The proposed model is able to predict the dynamic strength and damage of concrete. The model was implemented as a material subroutine (UMAT) in ABAQUS FE software for simulation of the concrete specimen behavior in Split Hopkinson Pressure Bar (SHPB). The SHPB is an apparatus which is able to apply different strain rates on a cylindrical specimen and sketch the stress curve related to a specified strain rate. Finally, the result of the proposed model was compared to the experimental results and a good degree of agreement was observed.

In this paper, general grains of solid propulsion systems such as cylindrical grains, multilateral grains and star grains are designed by new method. This method is more rapid in comparison with the others that act base on geometrical breakdown and boundary condition definition. In this method, geometrical definition point and grain production are defined and then the burning surface and geometrical burn back are calculated by analytical method. Benefits of this method are detection of surface and points joints without definition of type breakdown or grain type and direct calculation of burn back by solution of Cartesian equation. Mentioned method is a general technique to model the various types of grains. New geometrical configurations can be reached by this method which haven’t existed yet, so the code have less volume with more processing speed in comparison with the previous code. Visual FORTRAN code is developed which is able to calculate the geometrical burn back and zero dimension internal ballistic for every grain. Erosional burning velocity and temperature variation are modeled in this paper. Thrust, total pressure and temperature are illustrated vs. web burned variations. Finally, results of the burn back analysis code and the internal ballistic simulation code are evaluated by some other existent codes and real cylindrical grain test.

In this paper, the effect of strain rate sensitivity of materials in the case of a fully clamped circular plate has been discussed introducing a new criterion called "dynamic to static collapse pressure ratio". In order to do so, a simple mass and wire model is assumed. Then, using Cowper-Symonds constitutive relation and Perrone-Bhadra Simplifications, the mean strain rate of such a plate has been calculated. Experiments have been conducted on 5010 Aluminium and St37 Plates which were subjected to underwater explosion. According to the maximum deflection of each plate and the absorbed energy which is calculated by means of Duffey empirical relation, the dynamic to static collapse pressure of the plate is figured. Results showed that by increasing the strain rate, the average dynamic yield stresses of St37 and AA5010 plates are increased 2.3 and 1.5 times relative to their static yield stresses.