فصلنامه مواد پر انرژی
سال هجدهم شماره 1 (پیاپی 57، بهار 1402)

The Aim of this Research is to Analyze and Numerically Investigate the Penetration of Projectiles in Concrete Slabs Reinforced with Rebars and Perforated Steel Sheets by Nonlinear Finite Element Analysis Method and Using Abaqus Software. In this Research, Perforated Steel Sheets Have Replaced common Steel Rebars to Reinforce the Slabs. Perforated steel sheets have a good connection with the surrounding concrete due to their two-way function and the holes they Have, and they Create more Integrity in Reinforced Concrete Slabs. In this Regard, Models of Concrete Slabs Reinforced with Perforated Sheets and Reinforced with Rebars with Equal Volume Percentage of Steel under the Impact of Projectiles with Flat, Conical and Ajays Noses at a Speed of 630 Meters per Second are Simulated and has been Investigated. The Results of the Analysis Showed that the Use of Perforated Sheets for Arming Reinforced Concrete Slabs Instead of Reinforcement Increases the Strength and Strength of the Concrete Slab, Decreases the Projectile Speed, Decreases the Penetration Depth of the Projectile, Reduces the Kinetic energy and Absorbs more Energy in the Concrete Slabs.

One of the important issues in passive defense is to create the maximum attenuation of the blast wave. For this purpose, the current study focuses on reducing the shock wave using zigzag structures. The aim of this strategy is reflections and refraction of shock wave. Zigzag structure unlike the barrier approach by using minimal obstruction along the tunnel is performs attenuation. In this research, the amount of attenuation of the shock wave from the center of a tunnel with zigzag wall with 16 different zigzag cases and also one case without zigzag has been investigated. Numerical methods can predict the behavior of materials with appropriate accuracy and away from the limitations of experimental tests. From the numerical simulations, it can be seen that among the various designs of the zigzag structure, the maximum attenuation of the shock wave will be 79/74% at a distance of 19/5 meters from the explosion by a zigzag structure with a height and triangle base equal to1 meter. In this zigzag design, the initial shock wave undergoes reflection and refraction, which alternately reflects from one side to the other. This repetitive shock wave reflection helps to reducing the shock wave with virtually no blockage in the tunnel.

Using antioxidants in the composite propellants' formulations is inevitable. These materials are added to the propellant in order to increasing its stability during the storage and maintenance. In this paper, a simple, new and efficient method for the synthesis of some phenolic antioxidants from the reaction of 2-tert-butyl-4-methyl phenol with a variety of aliphatic and aromatic aldehydes in the presence of Lewis acids has been described. Phenolic products have been synthesized in mild, simple and safe method. The products have been characterized by their melting points as well as IR, 1HNMR and 13CNMR spectroscopies. In addition to high purity and high yields of the products, not needing to use of common corrosive, inorganic acids and the surfactant (generally sodium dodecyl sulfate) are as advantages of the present method.

The storage time of propellants is one of the important issues, the determination of which requires a precise analysis of the kinetic parameters of the decomposition reaction. One of the methods of investigating the decomposition reaction and determining the kinetic parameters of the thermal decomposition reaction is the use of thermal analysis. in this thesis, the thermal degradation reaction in a composite solid propellant sample based on PDEGA was investigated at several heating rates 5,10,15○C/min using differential scanning calorimetry (DSC). Then, using the model-free method of Kissinger and Ozawa, the average activation energy was determined at about 136 kJ/mol, then using a vacuum thermal stability test (VST), parameters of pressure and time in 3% degradation were obtained as 0.07563 bar and 91 hours, respectively and finally The shelf life of 38 years was calculated with Arrhenius mathematical equation.

In this research, the effect of dual curing agent TDI:DDI with different ratios on properties such as mechanical strength, elongation percentage, elastic modulus, hardness, burning rate and pressure exponent (n) has been investigated. Dimeryl diisocyanate (DDI) is a diisocyanate with long carbon chain, high molecular weight, low toxicity and low reactivity. In order to investigate the effect of the TDI: DDI double curing agent on propellant properties, five propellant formulations with the same loading rate and R value were produced and the prepared samples were tested for mechanical properties and burning rate. The results of the tensile test on the seventh day of the propellant curing process showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the amount of elongation increases, the tensile strength decreases and the modulus decreases with the passage of time. The results of the burning rate test showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the burning rate decreases. Comparing the propellants with different ratios of dual TDI:DDI curing agents with the propellant that is the only TDI curing agent, shows that as the amount of DDI in the formula increases, the pressure exponent (n) will decrease.

The burning speed can change in the presence of crack. Cracks cause an increase in the burning level and then increase the pressure in the combustion chamber, which will lead to a decrease in the optimal performance of the engine and sometimes accompanied by an explosion. In this research, samples of double base propellant were prepared by performing mixing operations in Kent, rolling in Walz machine and laboratory press. In order to check the cracks in the engine, sampling was done in the Walz machine at four different points of the engine. Also, the propellant press was performed in a laboratory press in different temperature conditions and with different material movement speeds. After that, crack detection was done by X-ray micro CT scan on engine samples. Results obtained for the press samples showed that the optimal conditions for the preparation of the propellant are the material movement speed of 10 and the temperature of 75 ˚C. Also, the results of Walls samples showed that by increase in homogenization process, the cavity radius in the sample decreases from 25.15 to 16.6 microns and the percentage of voids decreased from 3.5 to 0.5%.