فصلنامه مواد پر انرژی
سال یازدهم شماره 2 (پیاپی 30، تابستان 1395)

Plasticizers are compounds which add to solid propellants’ formulations to improve their mechanical properties. These materials have key role in the control of mechanical properties. 2,4-Dinitrotoluene (2,4-DNT) is one of the most important plasticizers of double based propellants. In this study, new series of Brønsted acidic ionic liquids (ILs) have been prepared and introduced as catalysts for the synthesis of 2,4-DNT plasticizer. The synthesized ILs were characterized by IR and NMR spectroscopies. The nitration reactions of toluene, 2-nitrotoluene and 4-nitrotoluene with nitric acid in the presence of these ILs were successfully done. Effective parameters such as solvent, temperature, molar ratios of the reactants and the catalyst amount on these reactions were investigated and optimized. High selectivity of the reaction, high purity of the product, use of green, non corrosive, non toxic and reusable catalyst are some advantages of this method.

In this work, nitration of low molecular weight polybutadiene (PB) by a convenient and inexpensive procedure has been investigated. The product (Nitropolybutadiene (NPB) energetic plasticizer) was characterized by FT-IR, 1H-NMR, GPC, TGA, DSC etc. Then NPB energetic polymer plasticizer and nitro-hydroxyl terminated polybutadiene (NHTPB) binder have been replaced with dioctyladiphate (DOA) inert plasticizer and HTPB binder in PBXN-109, respectively. The new formulation with energetic binder system as named PBXN-109EB. Density, hardness, vacuum stability, mechanical property, viscosity, glass transition temperatures (Tg), sensitiveness and performance properties of PBXN-109EB were compared to standard PBXN-109. It was found that new PBX not only has all requirements of PBXN-109, but also has enhanced performance properties in velocity, blast pressure, impulse and visual parameters of explosion. So NHTPB/NPB binder system (binder/plasticizer) can be used as a new energetic binder system in high performance polymer bonded explosives.

In this article, low velocity impact behavior of fiber metal laminate (FML) composite plates is investigated under three different impact energies (12.7 J, 16.3 J and 24.2 J). Here, three modeling techniques are used. In one of the models the inter-laminar damage is neglected (model without delamination) and in other two models this damage is simulated using cohesive element and cohesive surface models. Cohesive zone theory is used to model inter-laminar damage and Hashin failure criteria with energy dissipation-based damage evolution is used to model intra-laminar damage. In order to define plastic deformation of aluminum components, plasticity data and the Johnson-Cook plasticity model are employed and results accuracy of each model is compared to experimental ones. In the process of research, numerical modeling results in the terms of impact force and permanent deflection are compared and discussed with experimental results. It has been found that for 12.7 J impact energy in terms of impact force, model without delamination has the most precise result and by increasing impact energy force, accuracy of results is reduced. Whereas, two other modeling technique that include inter-laminar behavior, show more accurate prediction in higher impact energies compared to the experimental result. In which, cohesive surface model has the most accurate results. Also, the imposed damage in cohesive element and cohesive surface models are extracted and compared to each other. In addition, the results indicate that the predicted delamination in cohesive element and cohesive surface models are almost similar to each other.

In this article, the stress-time or speed-time relation for a steady intense shock wave front and effective parameters on it in solid metals (except alkaline metals) were studied. First, the parameters relevant to the deformation of a pure material were identified and a relation between them was found. Then with simplifying assumptions, a stress change equation was obtained. Afterwards, the modulus of the material was considered and after some simplification, it was substituted in the equation. After non-dimensionalization, effective parameters for a loading by an intense shock wave were obtained. The results of solving the dimensionless equations simulated the profile of the shock loading, gived the approximated rise time and width of the strong shock wave front and helped to explain that the maximum strain rate occurred near the centre of the shock wave profile. It was shown that when the local shear stress is higher than the lattice strength, a small step is formed on the particle velocity-time profile.

1,1-Dimethylhydrazine (UDMH) is used as a liquid fuel for missile and is a toxic matter. In this work to decontaminate UDMH from aqueous solution, hybridized photocatalytic and hydrogen peroxide oxidation processes have been used. The process was performed in a suspension reactor equipped with a UV-C lamp (150 W). Fe3O4@SiO2@TiO2 (FST) catalyst was used as a magnetic recyclable photocatalyst. To synthesize the catalyst, precipitation and sol gel methods have been applied and its characterization was performed using X-ray diffraction XRD, Fourier transform infrared FTIR, transmission electron microscopy TEM, and vibrating sample magnetometer VSM instruments. Effective parameters such as hydrogen peroxide concentration, amount of catalyst, and pH were optimized using response surface method. To analyze the amount of mineralization, the TOC analysis was used. The results showed that at the optimum conditions of [FST] = 85 ppm, [H2O2] = 800 ppm, and pH=7 the process could be mineralize 50 ppm of UDMH solution, about 79% after 120 min.

The presently available tear gas grenades used for controlling riot, have certain disadvantages like ability to re launching from rioters due to combustion at low temperature. More over on account of their considerable weight and volume, it was found difficult to transport sufficient number of them. In this regard, making a small grenade free from such disadvantages and to be mobile or gliding on the ground was the main topic of this paper, which includes description of chemical reaction in grenade for designing a nozzle in which the trust of output gases create movement in the grenade. Such a design can include determination of characteristics like throat diameter, nozzle length and its situation on the grenade in a way to provide the expected goals of the grenade. Modeling of the nozzle has been provided by ANSYS CFX software, the required calculations for choosing the body material specifications has been discussed and at the end, analysis of the grenade motion was presented. Due to the unavailability of the burning rate relation of tear material, a new algorithm is proposed to solve the problem.

In this paper, modeling of high speed projectiles with different nose shapes, penetrating into steel fiber reinforced concrete is investigated. This is a novel study because it considers the length to diameter ratio of steel fiber as well as projectile length to diameter ratio and volume fraction of fiber used in concrete matrix on the impact resistance of steel fiber reinforced concrete fibers at high speeds. Numerical simulation is used using LS-DYNA explicite code with Lagrangian method and axial symmetry form. The projectiles have an approximate mass of 45 (gr) and their velocities are about 2500 (m/s) penetrating into steel fiber reinforced concrete panel with volume fraction of 1.0%, 1.5% and 2.0%. In this article the exact behavior of steel fiber reinforced concrete confronting metallic projectiles at high speed is predicted. Here, Elastic-Plastic Hydrodynamic material model is used for prediction of projectile behavior. The results of the simulations are compared with experimental work of other investigators and, the results show that ogive nose projectiles are more efficient than other projectiles. In other words, by increasing the projectile length to diameter ratio from 0.5 to 0.9, for flat, hemispherical and ogive projectiles their residual velocities are increased. Also, it is shown that by increasing the volume fraction of steel fibers in concrete matrix, damage of top surface damage is reduced dramatically. The analytical model presented in this paper considers the speed variations of the projectile during the penetration process into steel fiber reinforced concrete is an important achievements this respect.