فصلنامه مواد پر انرژی
سال چهاردهم شماره 2 (پیاپی 42، تابستان 1398)

Plastic bonded explosive PBXN-103 as an underwater charge based on energetic binder system is uses in warhead section of several navy weapons. Metriol trinitrate (MTN), triethylene glycol dinitrate (TEGDN) and pelletized nitrocellulose are basic ingredients of binder system in PBXN-103 formulation. In this research the effects of applying accessible Poly glycidyl nitrate (PGN) as binder, were investigated on physical, mechanical, thermal, and sensitivity properties of PBXN103. Results remarkably indicated that the binder replacement enhanced the tensile strength and elongation to 85 psi and 70 % respectively. Based on differential scanning calorimetry (DSC), the thermal stability of formulation increased 20 °C in comparison with PBXN-103 and reached 190 °C. Glass transition temperature, vacuum thermal stability, impact sensitivity and friction sensitivity were -54 °C and 4.06 ml/g/48h, 7 N.m and 7.2 kg.F respectively. This new formulation was not fired by exploding No. 8 commercial electric detonator.

In the present work, the influence of formulation changes obtained by different compositions of double-base and modified double-base propellants, on the relaxation behavior was investigated using the dynamic-mechanical analysis techniques. In order to identify the dynamic-mechanical behavior and characterize the type of different relaxations and triple transition temperatures in double-base and composite modified double base (CMDB) propellants at the present work, DMTA test was used. According to the results, in spite of relaxation temperatures Tα and Tβ for the CMDB propellants, the other relaxation temperature T γ was not detected. By addition of energetics nitramines (RDX) to the modified double-base propellant, relaxation temperatures were increased. Decrease in values of nitroglycerine, also has the same effect on relaxation temperatures. The results were shown that for the samples containing RDX, the compression modulus was increased and for a more RDX content propellant sample, elongation at break was decreased.

Reinforced concrete (RC) structures are widely used in urban buildings and infrastructures, and these are always subjected to explosions caused by intentional or unintentional accidents. Among the structural members, columns are key load carrier elements. In this paper, behavior of RC columns with circular and square sections strengthened by steel jackets is investigated and compared under blast loading. Accordingly, six circular columns and six square columns, which are equivalent in geometry and material properties, were modeled using ABAQUS software package. The effect of varying the concrete strength, longitudinal reinforcement and geometrical properties of steel jacket on FE models of the columns has been studied. In addition, a sub-program has been written to evaluate the changes in axial and lateral capacity of the column. Based on the most important results, the circular columns perform better under blast loading. Using steel jackets, in addition to increasing the explosive capacity of the column, improves the effects of other remediation strategies such as the use of high strength concrete and the higher percentage of reinforcement. This effect was observed to be higher in circular columns in compare to square columns.

Red phosphorus (RP) is one of the most important allotropes of phosphorus with extensive military and civil pyrotechnics applications. During maintenance of red phosphorus, its decomposition generates phosphorus acid family and poisonous phosphine gas. One of the conventional method for evaluation of chemical stability of red phosphorus munitions is evolved phosphine measurement. In the present study, four samples of coated red phosphorus with ethyl cellulose, nitrocellulose and their combination with hydroxyl-terminated poly-butadiene (HTPB) were prepared. Then, the stability of all samples were characterized via water absorption measurment (as an effective parameter for chemical stability of red phosphorus) and evolved phosphine estimation(as ml of NaOH consumption in titration). Ethyl cellulose-HTPB coated sample exhibited best water absorption (37 and 38.8% reduction in water absorption at 24 and 48 hours compared to blank sample) and phosphine generation results (70% reduction in phosphine generation compared to blank sample) during chemical stability test compared to other samples. Then the aging process of this sample was evaluated and compared in a month with blank red phosphorus. Finally two pyrotechnic formulations containing blank and coated red phosphorus have been evaluated for phosphine release and thermal analysis(for calculation kinetic parameters according to Kissinger and Starink equations). The peak temperatures for both formulations containing red phosphorus appear in the range of 304 to 321, depending on the heating rate.

Due to prolonged storage time of fuel, recognizing the effective parameters on fuel degradation and its shelf life prediction is important. Regarding the need of using a reliable and efficient accelerated ageing method for prediction of fuel shelf life, introducing an efficient approach is necessary for this purpose. Most of the previous researches are limited to Arrhenius classical approach, and are rarely based on Berthelot one. The main objections of these two approaches are their exclusive application for isothermal ageing. In this work, a new approach called reaction severity index is proposed for predicting the shelf life of liquid fuels. Then, the shelf life of Samine fuel is predicted using this approach and compared with Arrhenius results at isothermal conditions. The predicted shelf life using this approach at 20, 30, and 40 °C is 5.64, 2.37, and 1.05 years, respectively. These results are in good agreement with the shelf life predicted using Arrhenius classical approach that predicts 5.69, 2.39, and 1.06 year, respectively. Therefore, the reliability of this approach makes possible to predict the fuel shelf life for storage conditions at ambient temperature.

The aim of this research was to investigate the effect of binary and tertiary curing agents on pot life of binder system based on HTPB using less reactive ones such as IPDI and HDI in combination with TDI. Polymerization rate in the presence of each of TDI, IPDI and HDI was individually studied using rheological method at 60 °C, where a two-step kinetic behavior (for TDI and IPDI) was observed. Measuring the pot life of binders using binary curing agent systems such as TDI:IPDI and TDI:HDI with 1:3 ratio, showed pot lives of 285 min (about 12% increase in comparison to single TDI system) and 195 min (about 24% decrease in comparison to single TDI system), respectively. The important point was abnormal decrease in pot life for binder system usnig TDI-IPDI binary curing agent, which can be related to catalytic role to HDI. In continuous, HDI was added to TDI-IPDI binary curing system (with pot life of 285 min). The pot life of TDI-IPDI-HDI tertiary curing system reached to 270 min (15 min decrease), which can emphasize again the catalytic role of HDI in the polymerization reaction.