فصلنامه مواد پر انرژی
سال چهاردهم شماره 4 (پیاپی 44، زمستان 1398)

Regarding the increase of terrorist threats and the possibility of blast events in the vicinity of industrial and residential buildings, the assessment of the resistance of all kinds of structures against the blast loads is very important. Concrete materials are more liable to threats than other kinds of structures Because of low ductility. One of the solutions is to use some kinds of engineered cementitious composites and fiber reinforced concretes. In this study, usage and employment of ultra-high performance fiber reinforced concretes (UHPFRC’s) that have high tensile strength and a considerable capacity of energy dissipation regarding the strengthening of the structures against the blast loading has been taken into consideration. In this regard, by choosing the material model based on the plasticity and damage for materials of ultra-high performance fiber reinforced concretes; first of all, the models of the columns made of UHPFRC during the field blast test done by other researchers’ studies, is simulated in a numerical manner and after ensuring the acceptable accordance of computational responses with recorded data during the blast test, using the modern method of jacketing with cover of ultra-high performance fiber reinforced concrete, the strengthening of the normal RC columns by using those jackets made of UHPFRC has been studied numerically. The results of numerical analyses show that the maximum displacement of models strengthened by UHPFRC will decrease considerably in proportion to unstrengthened models. For example, for 50 mm thick UHPFRC jacket, maximum mid-span displacement decreases about 63% (from 153 mm to 55 mm). Also, after generating the pressure-impulse (P-I) diagram, in order to assess the damage to the strengthened columns, it was made clear that by using the UHPFRC cover, the bearing capacity of the column against the blast load in the near and far field area, will increase considerably.

Earthquake and explosion are destructive dynamic forces. These forces can cause severe damage to the structure due to the time-dependent nature of the impact. One of the most important parameters for checking the stability of structures is the study of their buckling modes. The stability check has a direct relationship with the critical load of the columns. In this paper, the effects of simultaneous explosions and nearearthquake earthquakes on the stability of structures are investigated. The purpose of this research is to numerically simulate the state that earthquake-induced vibrations cause explosives to explode near structures. Therefore, the dynamic and buckling behavior of structures under the effects of earthquake and explosion have been investigated. In this article, the explosion enters the structure in three phases with the earthquake simultaneously. These three stages include before the earthquake, at the time of the earthquake and after the earthquake. In this regard, in this paper, structures are affected by internal and external structural explosions and the simultaneous effects of earthquakes. This article has shown that the most critical situation is when the vibrations caused by an earthquake trigger an explosion during its strong movement. The results of this paper show that the combination of explosion and earthquake is not very effective if the explosive is more than 500 kg TNT. In fact, earthquakes in this case have little effect on the nonlinear response of the structure. In this paper, it is shown that the effects of P-Delta consideration do not have much effect on the structure response. Based on the results provided for different explosions and earthquakes, it can be seen that the combination of explosion and earthquake has a greater effect on dynamic analysis.

Nowadays solid rocket motors (SRMs) are widely used because of simple structure and reliability. One of the requirements in SRMs is high tensile and bonding strength of liner for integrity of grain structure and neutralizes stresses applying to motor. In this research, effect of curing agent ratio (NCO/OH) in the range of (R=0.9-1.4) on tensile strength of liner and bonding strength of liner-propellant was investigated. Results showed, increase in isocyanate which grows crosslinking, increase the tensile strength and decrease elongation at break. In addition, with increase of NCO content, the ability urethane linkage formation in liner - propellant interface grows, therefore bonding strength increases. Finally, with considering of design requirements, processability, costs and safety the optimized NCO/OH ratio was selected.

The ammonium perchlorate (AP) is one of the useful oxidizer for making solid fuels, which is mainly produced by crystallization. In this study, the hydrodynamics of DTB crystallizer was simulated using Ansys Fluent in order to achieve a good understanding of flow pattern inside crystallizer which affects the CSD of AP. The hydrodynamic characteristics of crystallizer were studied for different sections of the crystallizer. The results showed that the upward flow inside the tube pushes the fresh feed to the boiling zone. Nucleation occurs in the boiling zone due to high saturation and shear stress of stream. The formed nuclei grow in the cross-section region between the tube and baffle in the presence of uniform downstream flow. In the classification region, the upward flow is uniform and slow enough to classify the crystals. Hence, this region is the best area to classify particles separated by the gravitational force.

Detonation initiation by shock is an important issue in the explosive safety assessment , design of the explosive train and explosive devices. Experimental studies in this area are very difficult, expensive, and require advanced equipment. Therefore, simulation is a useful and suitable way for studying this phenomenon. The purpose of this article is to develop a one-dimensional computer code for simulation of the direct initiation of energetic materials. The Fortran SIN hydrocode, was used for this purpose and the I&G burn model was added to this code. The developed code was used to simulate the direct initiation of the Comp-B by sustained shock pulses. A good agreement was observed between the present simulation results and the results of other references. For example, in the simulation of the initiation of Comp-B by 3.78 GPa shock, the run distance to detonation was 14.8mm, which the difference between this value and the reported experimental data is 5.7%.

This paper focuses on the design and analysis of an injector suitable for a liquid injection thrust vector control (LITVC) system. The LITVC system is used in flight systems to control and divert the thrust vector using the secondary fluid spraying method. For this purpose, various types of injectors were studied and categorized based on the geometry and operating conditions. The centrifugal single-base injector was selected as the design basis due to its uniform spraying, the ability to transfer higher flow rates, and relatively smaller geometric dimensions. In this process, in addition to defining three groups of non-dimensional geometric parameters, design was made based on engineering calculations and numerical solutions in FLUENT. The injector with proper outlet speed and the lowest pressure drop was selected as the final product of the design. Then, three different types of configurations were studied and the amount of thrust vector deflection created by each configuration was calculated. Findings were validated using the results reported by the previous researches, and finally, the best spray belt was introduced.