فصلنامه مواد پر انرژی
سال دهم شماره 2 (پیاپی 26، تابستان 1394)

Evaluation of thick-walled cylinders behavior under high strain rate loading is of great importance because of their many applications. Most of the studies around these structures were performed in the state of static and quasi-static. Therefore، development of analytical model in structures loaded with high rates in dynamic state and in complete plastic domain is valuable. The main purpose of this article is to derive a mathematical model based on plasticity flow rules in order to assess the expansion behavior of isotropic thick-walled aluminum cylinder containing TNT. Through this، the equations of radial and circumferential stresses derived from equation of equilibrium and then radial velocity could be calculated by iterative procedure applying instantaneous explosion product pressure as boundary conditions which is variable and depend on geometry of cylinder and also modification of dynamic strength at each moment with considering the strain rate. Therefore، strain rate with its effect on dynamic strength is of importance points in this article. After extraction of radial velocity، other process parameters will be determined and used as input data for the next stage. Furthermore، computer simulation was done، which shows good agreement with the analytical results.

A hypergolic bipropellant consist of fuels and oxidizers that can ignite rapidly upon mixing without external ignition devices. This self –ignition technology makes the engine ignition more reliable with the repeated use. Recently، ionic liquids with the dicyanamide anion showing good hypergolic properties when contacted with common oxidizer (such as concentrated nitric acid)، have attracted a lot of attentions. In this study، two new hypergolic ionic liquids with imidazole cations and energetic dicyanamide anions have been designed and synthesized. The synthesized ionic liquids was characterized by 1H-NMR and FT-IR، and their thermal properties were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results suggested that these ionic liquids have good thermal stability (approximately up to 200 °C without significant weight loss) and phase change curves shown good agreement with the changes in weight loss by increasing temperature. In addition، hypergolic properties of synthesized ionic liquids were investigated by drop test in the presence of concentrated nitric acid following which، they shown spontaneous ignition in contact of oxidizer surface.

Polycaprolactones due to the polar groups in their structures are able to be mixed with other nitrate esters and thus are presented as suitable binders. In the other hand, polyglycidyl nitrate with ONO2 groups is a high energetic polymer; however, it has not suitable mechanical properties. Consequently, it is possible to use the favorable mechanical properties of polycaprolactone and energetic properties of polyglycidyl nitrate by the synthesis of the PCL-PGN-PCL three-block copolymer. In this research, the PCL-PGN-PCL three-block copolymer was synthesized for the first time. Firstly, polyglycidyl nitrate as a monomer was synthesized using epichlorohydrin (60% total yield of the reaction). Then, polyglycidyl nitrate was synthesized by using this monomer (70% yield). Finally, the new PCL-PGN-PCL three-block copolymer was synthesized by ring opening polymerization of caprolactone as monomer and polyglycidyl nitrate (PGN) as a macro initiator in the presence of dibutyl tin laurate as catalyst. The differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were performed to investigate the thermal characteristics of this copolymer (Tg -45.2 °C). In addition, there was one pick in the GPC chromatogram that proved the formation of PCL-PGN-PCL three-block copolymer. The PCL-PGN-PCL three-block copolymer was characterized by 1HNMR, 13CNMR and IR spectroscopy methods. In the last part, the synthesis process of the PCL-PGN-PCL three-block copolymer was optimized. The reaction conditions were optimized at 115° C for 19 hours using 1mol% of catalyst. Toluene was chosen as a solvent and the monomer was added gradually into the reaction media. The yield was 81%. Also, the molar ratio of monomer to initiator as 5:1 showed the best molecular dispersity.

In this study, the effect of Fe3O4-coated graphene as nanocatalyst on the kinetics degradation of Ammonium Perchlorate and Glysydyl Azide Polymer (AP/GAP) composite propellants is investigated in order to modify and improve the burning rate of propellants. The SEM-EDX and EDX-Mapping surface analysis methods were used for structural and morphological study of the propellant containing nanocatalyst. The results showed that all the samples were homogenous. Thermal analysis techniques (DSC and TG) were used in the presence and absence of the nanocatalyst in order to investigate the thermal behavior of the propellant. The results showed that Graphene@Fe3O4 reduces decomposition temperature and merge decomposition peaks of AP. This will probably speed up the process of thermal decomposition of AP in the propellant. Moreover, the thermal decomposition kinetics of the samples were investigated using TGA analysis data and Friedman, Ozawa, and Flynn-Wall-Ozawa (FWO) methods. Then the activation energy of the samples were calculated. The results showed that the required activation energy in the presence of Graphene@Fe3O4 was less than in the absence of the catalyst, improving theperformance of propellant.

Hydroxyl terminated polybutadien (HTPB resin) is a liquid hydrocarbon polyol that is commonly used in the preparation of solid composite propellants. Because of unsaturated nature of HTPB polymer, it has high potential for oxidative aging. In this paper, the change in the properties of two types of HTPB resin under thermal oxidative aging in the presence and absence of phenolic antioxidant have been investigated. For this purpose, two samples of resin have been stored at 60 °C during four month under atmospheric pressure and the changes of the peroxide value, hydroxyl value, epoxy number, viscosity and molecular weight have been investigated. The results show that crosslinking of radical chains, increase of the molecular weight and hydroxyl functionality of HTPB are the most important oxidative events that occurred during oxidative aging.

In the present paper, nonlinear dynamic analysis of low-velocity impact of rectangular composite plates reinforced by SMA strips is investigated and the effects of the instant phase changes and the local and istatantaneous non-uniform distribution of transformation of the austenite to martensite phases and vice versa is considered, for the first time, implementing a written user defined material subroutine code in the ABAQUS/EXPLICIT finite element analysis code. In contrast to the available models which have used the approximate plate theories, a 3D finite element simulation is utilized for extracting the impact responses based on the elasticity theory. Finally, effects of different parameters such as the in-plane preloads, eccentricity, and indenter energy on the impact responses of the hybrid composite plate are investigated. The simulation results indicate that the SMA can absorb a remarkable portion of the stored impact-induced strain energy due to the superelastic and hysteretic natures of the SMA material, which results in increasing impact strength of the composite plate and decreasing the damage caused due to the impact. Moreover, results show that in the cases of the eccentric impact and presence of the tensile preloads, the contact force increases due to the less movability of the impacted point of the plate; a fact that may lead to higher damages.

Nitro functionalization of alkenes has particular importance in the field of energetic materials due to unsaturated nature and the ability to synthesize a wide range of C-nitro aliphatic compounds. Considering the importance of these compounds, the use of nitrile iodide as a mild, inexpensive and safe reagent to nitro functionalization of HTPB as an unsaturated prepolymer was studied in this paper. In order to optimization of the effective parameters on the synthesis of Nitro-HTPB, the proportional amounts of reactant, amount of solvent, temperature and reaction time were investigated and the effect of these parameters on the efficiency of nitro functionalized products was evaluated. It was observed that the kind and amount of solvent have a significant impact on the quality of product. In this regard, 24 hours of reaction time at room temperature were considered as optimal conditions. Finally, differential scanning calorimetry (DSC) method was used to study the effect of the amount of nitro group on the thermal behavior of the products. It was observed that by increasing the nitro group amount of products, thermal stability decreases and heat of decomposition increases.