فصلنامه مواد پر انرژی
سال شانزدهم شماره 1 (پیاپی 49، بهار 1400)

In this article aging behavior of composite solid propellant was investigated by determining its mechanical properties at elevated temperatures. For this purpose, three HTPB samples with different microstructures were selected and composite solid propellants were prepared based on them keeping similar other components and aging was studied by accelerated method. Mechanical properties were measured after accelerated aging using dynamic mechanical thermal analysis (DMTA) in order to investigate the effect of HTPB microstructure on composite solid propellant aging. Results showed that with increasing molecular weight, hydroxyl value, increasing vinyl and decreasing cis contents in resin microstructure, the mechanical behavior of the propellant becomes more rigid, which may be due to limiting the polymer chain mobility or facilitating post-curing crosslinking. Over aging time, the shelf life changed effectively with propellant binder microstructure. The obtained shelf life for the composite solid propellants based on D01, D02 and D03 resin samples were 6, 4.48 and 3.56 years. The results showed significant differences and show well the affect of the micro-structural properties of HTPB resin on the aging of its-based composite solid propellant. 

One of the properties for liquid bipropellants is their hypergolicity. The required quantity for this purpose is ignition delay time (IDT). IDT is classified into two classes: physical and chemical. The chemical ignition delay time is the time interval between the contact of fuel droplet - oxidizer surface and appearance of the first flame. The most appropriate laboratory method for measuring the chemical ignition delay time is drop test. Considering the effective parameters on the ignition delay time (such as oxidizer to fuel ratio, temperature and pressure) and following the mechanical design, this system was manufactured with capability of temperature and the reaction chamber pressure adjustments. For calibration and standardization of the system, some liquid fuels (such as triethyl amine, unsymmetrical dimethyl hydrazine and Tonka-250 mixture) and some liquid oxidizers (such as strong nitric acid and conventional oxidizer AK27) were applied. Good repeatability and dispersity of the obtained results indicate the system accuracy.

In this research, a reliable and simple method was described for the determination of the amount of titanium dioxide (TiO2) in double base solid (DB propellants), based on a comparison with the inductively coupled plasma method. The method is based on complex formation of Ti(IV) with chromotropic acid in acidic media and monitoring the absorbance of the colored products by spectrophotometric technique at 460 nm. Under optimal conditions, the calibration graph was linear in the range of 0.10-5.0 μg mL-1 of Ti(IV) with the limit of detection of 0.05 μg mL-1. The validity of the method was evaluated by means of the data statistical analysis. For this purpose, the method was applied to the determination of titanium dioxide in DB propellants, and the results were compared based statistical tests with those obtained by the ICP- AES. The results showed that the proposed method offers an accurate and reliable approach for the determination of TiO2 in DB propellants, and can be suggested as a routine method in quality control laboratories.

In the current research work, a zero-dimensional code for the internal ballistic of gun analysis has been developed with a deterrent layer propellant. Today, the driving of the deterrent layer is widely used in small and medium-caliber weapons. The deterrent layer is in the form of a thin coating on the surface of a single base or double base gun propellants. The main purpose of this type of propellants is to increase the muzzle velocity by observing the maximum allowable pressure for the weapon. It has been developed for internal ballistic analysis of the thermodynamic model or the next zero-based on Badr software relations. In order to validate the analysis results, experimental results and results of other valid codes related to 20 mm weapon and 30 mm laboratory weapons were used. The code is able to analyze the combustion of two-layers propellants with a variety of conventional geometries for a grain. The effect of the engraving force on the accuracy of the examined results and the impact of deterrent layer on internal ballistic of gun performance has been discussed. The results show that in case of using the deterrent layer with increasing the load density can be reach to higher muzzle velocities with maintaining maximum allowable pressure. The investigation on M55A2 ammunition demonstrated 9.5% increasing in muzzle velocity by using of deterred propellants rather than undeterred propellants.

One of the most important issues when working with energetic materials is their initiation. Of the various methods of energetic materials initiation in the military and civilian industries, shock initiation is of particular importance. Numerical and simulation study of the shock initiation of condensed phase explosives is related to models called burning rate models, which describe the conversion rate of unreacted materials to detonation products. Among the burning rate models that have been proposed for explosives so far, the Ignition and Growth (I&G) model is one of the most popular and widely used models. In this paper, the genetic optimization algorithm is coupled with an upgraded Fortran SIN simulator hydrocode. The calibration was based on minimizing the difference between the calculated pressure data and the experimental data obtained from manganin pressure gages in the shock initiation tests. The results of optimizing the I&G parameters for Comp-B demonstrates good accuracy of the algorithm; So that after calibration, the difference between the pressure history obtained from the calculations of this paper and the experimental data was about 15% and in this respect is about 6% more accurate than the results reported in previous reseorches.

In order to protect a blast loaded structure, three ways can be utilized: “increasing the stand-off using natural or artificial barriers”, “increasing the structure strength or performance level”, “decreasing the energy of blast using the passive, semi active, active and hybrid control methods”. In recent method, using controlling mechanism and tools, the effect of blast waves is decreased and the structure response is controlled. In this research, considering the third way, two systems including mass, spring, friction damper and viscous damper is presented and its performance reducing the response against blast is evaluated utilizing numerical analysis. In the first innovative system, there is a mechanism with a spring, a massless ball and a sloped surface and in second innovative system, there is a mechanism with a viscous damper, a massless ball and a curved surface. Results shown improvement in performance up to 40 percent. Generally, inability of system to endurance the maximum responses leads to damage and collapse of structure underging blast load. Thus, finding an effective mechanism to achieve an acceptable structure performance and to decrease system overshoot, can help to design of the structure enduring the blast.