فصلنامه مواد پر انرژی
سال پانزدهم شماره 1 (پیاپی 45، بهار 1399)

In this paper, the sympathetic detonation is studied. In this type of detonation, the shock wave of an explosive by passing through a neutral environment (gap) induces the detonation in the second explosive. The study of this phenomenon is important to the safety of the ammunition depot and their transportation. In the present study, the sympathetic detonation in Comp-B has been studied. In this regard, the effect of the thickness of the gap and the type and composition of the materials used as the barrier in preventing the occurrence of sympathetic detonation has been investigated. The results showed that a thick layer of fine sand, held by thin layers of polymeric material, is more efficient than other materials and can prevent sympathetic detonation well. The results indicate that a 20 mm single iron barrier and also 20 mm barriers consisting of sand + Plexiglas, sand + epoxy and sand + rubber prevent from the sympathetic detonation of the Comp-B acceptor.

In the present study, the effect of explosive welding stand-off distance on the structure and corrosion behavior of aluminum alloy 5083-copper joint is studied. The microstructure was examined by optical microscopy and scanning electron microscopy and corrosion behavior with potentiodynamic polarization tests and electrochemical impedance spectroscopy in a salt environment. Microscopic results showed that as the stand-off increased from 1.5 to 2.5 mm, the joint interface changed from smooth to wavy, and the local melting thickness increased in the joint interface. Comparing the results of the energy distribution spectroscopy, it was found that the concentration of aluminum in the local melting zones of the interface increases with increasing stand-off distance. There are also cracks perpendicular to the joint in the local melting zone. As the stopping distance increases, the corrosion rate increases, which is due to the increase in kinetic energy and plastic deformation in the joint interface, changes in the concentration gradient, and increase in the thickness of the local melting layer.

“Cold-formed steel (CFS) stud walls” are innovative alternative for construction of walls in buildings. The main frames of CFS walls consist of a group of vertical members called “studs” which are hold by fasteners within two horizontal members called “tracks” at the upper and lower ends. One of the conventional ways for designing and analyzing of CFS stud walls under blast loading is to employ proper “static resistance functions” of studs. These functions, as the representative of system resistance, permit simplification of CFS stud walls into an equivalent single degree of freedom system for further dynamic analyses under blast loading. Providing adequate lateral bracing is a vital measure to make use of studs’ flexural resistance. If not, lateral-torsional buckling of studs prevent from full utilization of their flexural resistance and subsequent tension-membrane resisting mechanism. Therefore, this study deals with the effect of lateral bracing of studs on the expected resistance of walls exposed to the blast pressure waves. To this end, by adopting a portion of a conventional stud wall and performing finite element analyses, the minimum required bracings and their optimum positions have been determined. Accordingly, make use of two bridges at middle fifth of the stud wall’s span was found as the optimum alternative for the lateral bracing under equivalent blast pressure.

In general, due to the role of traffic tunnels, structural safety and defense considerations in these structures are very important. The structural lining of the tunnel can cause a lot of damage under the internal explosions resulting from malicious operations. Therefore, it is important to investigate the impact and damage caused by it. In this paper, the gas explosion at a height of 3 meters above ground level in the middle of the tunnel is modeled as the energy equivalent of 250 kilograms of TNT. A fully coupled numerical model has been made as the fluid-structure interaction (FSI) effects. To evaluate the dynamic parameters of the structure, the displacement and velocity in five points of the tunnel were investigated. In this research, engineering characteristics of one of the existing tunnels have been considered and two D shape and circular cross sections with a width of 6 meters are used to develop models. The overall results indicate that in because of the damage caused by the internal explosion, the tunnel is damaged and the maximum velocity generated at the D shape cross section is larger than the circular section, but the displacement is lower.

In this work, thermochemical and ignition characteristics of a pyrotechnic compound containing Zirconium and Fe2O3 (Zirconium as a metal fuel and Fe2O3 as an oxidant) was studied. The influence of the fuel to oxidant ratio on the rate and behavior of ignition of Zr-Fe2O3 pyrotechnic system was investigated. Burning rate increases with the increase fuel fraction until 60%. Therefore, the delay times of the mixtures were in the order Zr(70)-Fe2O3(30)> Zr(50)-Fe2O3(50)> Zr(60)- Fe2O3(40). On the other side, order of combustion pressures of mixtures was in opposition of mentioned order. The obtained Zr-Fe2O3 mixtures were thermally stable up to 500°C. Based on the results, the Zr-Fe2O3 composition can be used as pyrotechnic millisecond delays because of its high combustion rate and heat and acceptable thermal stability.

One of the intrinsic properties of foams, porous materials, and granular materials, are their ability to mitigate the blast wave. The current research study investigates the capability of granular materials in the mitigation of blast wave both experimentally and numerically. In the experimental section, the explosion shock tube facility was employed to conduct a series of experiments. Sawdust and mineral pumice were used as granular materials in the sandwich panel core and their mechanical properties were obtained by performing quasi-static compression tests. Moreover, the commercial hydrocode AUTODYN was used to numerically simulate the process while the smooth particle hydrodynamics method (SPH) was employed to model granular materials. The obtained results indicate that mineral pumice leads to more mitigation of the blast wave compared to sawdust. Besides, using a low thick core made of granular materials is not considerably effective and using a high thick core leads to more mitigation of the blast wave.