فصلنامه مواد پر انرژی
سال دوازدهم شماره 4 (پیاپی 36، زمستان 1396)

In the present research, the influences of explosive welding parameters on the corrosion behavior of the three layer explosive welds of the tubes Al 5083 / Al 1050 / stcr18Ni9Ti in the salt environment was investigated. The selected parameters included the stand-off distance and the thickness of the explosive charge. Therefore, two samples A and B were welded with stand-off distances of 6 and 6.75 mm respectively. The results showed that with increasing the standoff distance, the straight interface transited to the wavy interface. The results showed that, with increases in the standoff distance, the hardness near the interface was increased. The results of the electrochemical impedance spectroscopy showed that the number n in sample A is lower than that of sample B and as a result, the corrosion current in sample A is higher which leads to the reduction of the charge transfer resistance. The increase in the transferred impact kinetic energy in the sample with higher stand-off distance and explosive charge thickness was also effective on the increase in the corrosion.

In this research, the thermal stability and decomposition kinetics of pentaerythritol tetranitrate (PETN) and Pentastite explosives have been studied experimentally using non-isothermal differential thermal analysis (DTA) and thermo-gravimetric (TG) methods at heating rates of 4.0, 6.0, 8.0 and 10.0 °C/min. The kinetic parameter of activation energy (Ea) and critical ignition temperature for thermal decomposition of these explosives have been evaluated by the model-free methods proposed by the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The Vyazovkin isoconversional method was used without need for the Arrhenius factor and reaction mechanism. The mechanisms of the reactions and mass loss route of the samples in different temperatures were predicted and compared with the results of advanced kinetics and technology solutions (AKTS) software. The mean kinetic parameter of activation energy of exothermic decomposition of the PETN and Pentastite explosives as calculated by the Kissinger, Ozawa, Ozawa-Flynn-Wall and KAS methods were 129.1 kJ/mol and 161.9 kJ/mol, respectively. These results were used to estimate the mass loss and predict the lifetime of the explosives. , and also they were statistically compared to experimental accelerated aging and AKTS results and showed satisfactory outcomes at > 100.0 °C.

This paper is investigated the effect of impregnation of the high modulus polypropylene shear thickening fluid. Fluid using silica nanoparticles dispersed in polyethylene glycol in both 42% and 44% has been achieved. The penetration tests conducted in this study is in accordance with NIJ 0101-04. The results are evinced that the penetration resistance is improved by impregnation of high modulus polyethylene fibers. This resistance was saliently affected by percentage of nanoparticles dispersed in polyethylene glycol. Whereas by increasing 2% of nanoparticles dispersed in polyethylene glycol (from 42% to 44%), the penetration resistance is increased about 38.9 %. When the carbon Nano tube is inserted in shear thickening fluid, due to reduction of the friction between projectile and target, results decrease in penetration resistance of polypropylene target. When the number of layers is equal, the penetration depth in backing material when 44% impregnated polypropylene fabrics is tested against spherical projectile, is 67.39 percent lower that non impregnated fabrics.

In this research, progressive damage of woven composite materials due to high velocity impact is investigated via finite elements method. Necessity of impact analysis of composite materials using progressive damage method is detailed and available material models for this type of analysis is discussed. Governing equations at onset of failure and failure modes as well as damage growth is expressed. Stain rate effects are contained in dynamic modulus and strength of composite materials. A user defined material model was supplied in LS-DYNA. Different failure modes such as axial failure in fibers due to tension or compression, in-plane lateral and shear failure, out of plane failure and delamination and crushing may be simulated. Ballistic impact in four and eight layered composite targets is investigated using this UMAT. Variation of projectile velocity in terms of time is studied on velocities less than and more than ballistic limit velocity. Two different responses are achieved by considering or neglecting strain rate effects. Also, variation of elastic modulus and strength in fiber direction as function of strain rate and damage growth is investigated for near field, far field and midrange of impact zone.

The VLIP is a usefull system to compare the high explosives efficiency. This device includes a metallic plate which located above the explosive material and upthrown vertically due to the explosion. The exerted impulse on the plate is used as a meter to determine the explosives efficiency. Since the VLIP system has a low cost, in this paper a method based on VLIP is presented to determine the TNT equivalency of explosives. In this order airblast near the VLIP plate was simulated numerically at first and then compared with experimental results to confirm the simulation accuracy. Thereafter, relation between the exerted impulse on the VLIP plate and TNT equivalency of explosive material was studied. The results showed that VLIP could not be directly utilized for determination of the explosives TNT equivalency. In fact, performing of some explosion tests on the TNT samples with various weights and recording of the exerted impulse on VLIP plate is essential. These tests help to calibrate the VLIP and then it could be used to determine the TNT equivalence of other explosive materials. In the present paper, some equations were derived based on the mentioned method to determine the TNT equivalency of new explosives by VLIP apparatus.

PBXN-111 is a cast cured underwater explosive containing RDX, ammonium perchlorate, aluminium powder and HTPB binder. In this research, the kinetics and thermodynamic properties of thermal decomposition of this PBX investigated by Kissinger and Flynn-Wall-Ozawa (FWO) methods based on differential scanning calorimetry under non-isothermal condition with heating rate of 5, 10, 15 and 20 °C/min. Results showed that this charge has thermal stability exceed 200°C. As heating rate in thermal analysis increased, decomposition temperature of RDX, as first unstable ingredient in PBX, increased slightly. Activation energy of RDX decomposition reaction in PBXN-111 increased 16% in comparison with pure RDX. Average enthalpy, Gibbs free energy and entropy of thermal activation were 311.34 kJ/mol, 122.57 kJ/mol and -373.69 J/mol.K, respectively. In addition, average amounts of critical temperature for thermal explosion and 500-day cookoff temperature of PBXN-111 are 198.35 °C and 120.95 °C, respectively.

Chemical stability in propellants is important issue. In this article chemical and thermal stability for two kinds of double and single base propellants are investigated. In mass loss test in 90 0C, after 18 days mass loss for both samples is no more than 3%. By stabilizer measurement it was evident that remaining stabilizer content in aged samples are more than 10% in relative to fresh samples. Also kinetic calculation results from Differential Scanning Calorimetry (DSC) Shown no obvious changes for heat of reaction and kinetic parameters. In vacuum stability test, All samples except double base propellant which was aged in 90 °C released less gas volume in relative to standard. Also released gas from this sample are identified by ion mobile spectrometry it was evident that main composition of released gas is nitrogen oxides. Releasing NOX gases indicated that this sample is in autocatalytic State.