نشریه دفاع هوافضایی
پیاپی 4 (زمستان 1401)

In this article, new research is based on density functional theory (DFT), and simulation of first-principles calculations, to investigate the effects of vertical compressive strain on the properties of two-dimensional penta-graphene nanostructure. First, to validate this research's results, the structural and electronic properties of penta-graphene were investigated in the optimal state, and the results show a good agreement with previous research. Investigating the electronic properties of penta-graphene under the conditions of compressive strain indicates the change of the energy band gap from indirect to direct. Also, the examination of the optical properties of this two-dimensional nanostructure under compressive strain conditions shows the compatibility of this nanostructure's optical and electronic behaviors. According to the results obtained in this research, the two-dimensional nanostructure of penta-graphene can be introduced as a suitable material for the design of electro-optical devices.

The experimental and numerical study on flexural behavior of new type sandwich structures with glass-epoxy skins and a combinatorial core consist of foam and corrugated composite with rectangular geometry was investigated in this paper. After sample production by vacuum assisted resin transform molding technique; samples were tested according to standard and then the related load-deflection curves were obtained. Finite element analysis was applied for determining maximum deflection of samples by ABAQUS software. In experimental three series of samples with combinatorial core and three different thicknesses for rectangular shape corrugated composite in a foam core and one series of sample with simple foam core; have been product. In order to experimental accuracy of problem; three same samples have been product in each case and the average data have been used for results. It has been shown that the flexural stiffness was increased with increasing in thickness; and the flexural stiffness to mass ratio was increased so on; but the rate of this increasing was decreased from 3 to 5 layers of corrugated composite laminate in PVC foam. Finally the experimental and numerical results were compared and a reasonable agreement between them has been observed.

Nitride multilayer coatings created by Physical Vapor Deposition (PVD) method has shown a good trend in improving corrosion resistance. In this research, corrosion performance of Ti/TiN multilayer coatings with 1.5 µm in thickness which created by High Vacuum Magnetron Sputtering on 7075 Aluminum Alloy substrate was investigate.  Presence of TiN, TiOxNy and TiO2 phase in the cross-section of multilayer coatings was confirmed by XPS analysis. Creation of uniform coatings with tough surface with smooth grains by FESEM microscope and surface roughness of 142Å by AFM microscope was confirmed. Electrochemical Impedance Spectroscopy (EIS) results was proved desirable corrosion behavior of the Ti/TiN coatings. Resistance changes for coated samples was in range of 1984-808.5  witch in comparison with uncoated sample with 84.3 in resistance was shown remarkable increase in corrosion resistance between 9.6-23 times.

Array of nano-field emitters is used in devices such as vacuum tubes that are used in military equipment such as radars and electromagnetic weapons. These arrays have been realized based on carbon nanotubes (CNTs). In this article, carbon nanotube and zinc oxide (CNT–ZnO) nanocomposite were successfully synthesized with a different method. We have initially prepared multi-walled carbon nanotubes (MWCNTs) by the plasma enhanced chemical vapour deposition method. Alternatively, we used thermally physical vapour deposition for making thin Zn film to oxidize it later. Scanning electron microscopy and also Raman spectroscopy measurements of the prepared samples confirmed the presence of ZnO nano particles on the CNT bodies. By field emission (FE) measurements we found that ZnO deposited CNTs have a more efficient emissivity than that of CNTs alone.This composite can be used instead of cold cathode in vacuum tubes that work based on field emission properties. Before this, such tubes have been made with pure CNTs.

Given the sensitive situation of the country and the successive threats, as well as several terrorist acts in the coming years, the need for passive defense is felt at any other time. Therefore, in these cases, the need to protect sensitive resources is essential. Geosynthetics are among the new and efficient materials that, while simple and fast implementation without the need for equipment and specialized people in combination with soil as protective walls, show good performance even compared to time-consuming, costly and time-consuming structures. In this study, the focus is on the deformation of the reinforced earth wall in the face of an explosion. After examining the model by Geostudio / Slope / w geotechnical software in static equilibrium mode, wall deformations were performed by 3D / Abaqus finite element software using MohrColumb behavioral model. The aim of the present study was to investigate the effect of geosynthetics on the deformation of reinforced earth walls against explosion. The results showed that with increasing the distance of the explosion from the wall, the deformations of the wall decrease, but the remarkable point is the rate of this deformation reduction, which increases with increasing the distance of the explosion from the earth wall

Maintaining the readiness of operating air defense equipment as one of the most important arms of the country's armed forces, it is inevitable. Defensive weapons (especially anti-aircraft guns) require full readiness to fire in a fraction of a second. In Iran, due to the installation of this equipment in areas with high humidity (such as the coastal areas of the Persian Gulf), the need for corrosion protection is essential. For this purpose, the production of polyurethane / graphene protective coating on simulated steel from the body of conventional defense cannons (23 and 35 mm) was investigated. In this regard, three types of polyols with plant base (castor oil) were synthesized. Graphene oxide, porous graphene and amine porous graphene were also used as coating nano fillers. The purpose of amino acidification and porosity in graphene was to increase its compatibility and contact surface with polyurethane. The parameters that were studied as variables in the experiments are the type of polyol, the type and amount of nanoparticles applied to the system. After the samples were synthesized, thermal, adhesion, tensile strength and immersion tests of salt water were performed on them and scanning electron microscopy (FE-SEM) was used to study the surfaces and particle dispersion. Finally, it was found that the nanocomposite synthesized from semi-rigid polyol with porous amine porous graphene has better properties than other samples and can withstand the body of anti-aircraft cannons against corrosive environments with high humidity.