The influence of welding speed on mechanical properties of friction stir welded joints of AA2024 T351 aluminum alloy

The aim of this study is to analyze how the process parameters affect the mechanical properties of butt joints obtained by friction stir welding (FSW). The experimental study was performed by the FSW of sheets having a thickness equal to 6 mm and made of aluminum alloys AA2024 T351, varying the process parameters, namely rotational speed and welding speed. The following welding parameters were used: the rotation speed of the tool did not change and amounted to 750 rpm, and the welding speed was 73, 116,150 mm / min. The welds were obtained without the presence of errors and with an acceptable flat surface of the compound. Tensile tests were performed orthogonally to the welding direction on specimens having the welding nugget placed in the middle of gage length. Vickers hardness measurement was conducted perpendicular to the welding direction, a cross-section of the weld joint. The hardness profiles were obtained along 3 horizontal and 63 vertical directions. Bend testing was carried out according to EN 910 The bending specimens were tested using face and root side of the joint in tension.

An approach of constant false alarm ratio for improved target tracking

Each radar has the function of surveillance of certain areas of interest. In particular, the radar also has the function of tracking moving targets in that territory with some probability of detection, which depends on the type of detector. Constant false alarm ratio (CFAR) is a very commonly used detector. Changing the probability of target detection can directly affect the quality of tracking the moving targets. The paper presents the theoretical basis of the influence of CFAR detectors on the quality of tracking, as well as an approach to the selection of CFAR detectors, CATM CFAR, which enables better monitoring by the Interacting Multiple Model (IMM) algorithm with two motion models. Comparative analysis of CA and CATM algorithm realized by numerical simulations has shown that CATM CFAR gives less tracking error with proportionally the same computer resources.

The influence of the internal ballistic pressure on the rifled barrel stress response

This paper focused on the 12.7 mm gun barrel stress response caused by the pressure of the gunpowder gases. During the firing process, the barrel is loaded by different mechanical, chemical and thermal loads. In this paper except the pressure of the propellant combustion, all the other loads were ignored. The pressure loads are obtained with a mathematical model of the interior ballistic. The Lame equations for the thick-walled cylinder were used to calculate the barrel stress response. The loads are applied on a certain barrel cross-section for a defined time. Two 3D models of the barrel with and without grooves were used to perform a numerical simulation. A comparison between results for the two types of barrels shows a good agreement between the stresses obtained by the analytical and numerical methods.

Biogas equipment for electricity and heating

The paper gives an example of a biogas plant used for electricity and heat production. First, the role and importance of the biogas plant is presented, then an overview of the raw materials used for biogas production is given, a project of the biogas plant with constituent elements is given, as well as a description of the technological process and elements of the biogas plant. The calculation of biogas consumption for the needs of the power plant of 0.999 MW has also been performed.

Effect of sensitization on corrosion properties of TIG welded Al-Mg alloy

The effect of sensitization on the intergranular corrosion (IGC) of TIG welded AlMg6Mn was investigated by means of scanning electron microscopy (SEM) and corrosion NAMLT tests. The as-received hot rolled AlMg6Mn alloy plates with a thickness of 8 mm were welded by TIG welding with S-AlMg5 as a filler material. Specimens were sensitized at 100°C for 7 days. It was found that welded specimens are sensitive to IGC. The. mass loss in NAML test was 106.7 mg/cm². The welding increases the susceptibility to IGC, since the mass loss of the base metal at the same test was 70.7 mg/cm². The increase of susceptibility to IGC is attributed to significant continually precipitated Mg-rich phase along the grain boundaries during the sensitization treatment.

A new methodology for designing of tactical integrated telecommunications and computer networks for OPNET simulation

This paper present a novel methodological approach in the design of integrated tactical telecommunications and computer networks for command information system and defining the elements for the OPNET simulation model. The elements proposed for design of network information architecture. For that purpose, the way established to set up relationships between elements that uses for network topologies design, building of network elements and network traffic. They are integrated with its parameters in the preliminary model defined by an OPNET simulation model. We propose the measure of efficiency for accomplishment of tactical command requirements to use the design model network. This measure of efficiency is mean time delay that described with mathematical relations, involving the communication parameters speed of generating traffic, packet size, link capacity and adequately reflects the projected network. Furthermore, the applications of the proposed approach and given instructions allow to designers full examination of the network architecture, and provide translation into preliminary model and design OPNET simulation model.

Behavior tests of a new form of propulsion after ship reconstruction

The subject of this paper is a detailed qualitative analysis maneuvering and propulsion characteristics of a special purpose river vessel "KOZARA" River war flotillas of the Serbian Army, after reconstruction and modernization. With the modernization of the ship, among other things, the old propulsion group with a classic diesel engine propulsion was replaced by a new diesel electric propulsion. In order to assess the justification of this replacement from the aspect of expected improvements of shunting and propulsion characteristics of the ship, it was necessary to develop and implement a test program and compare the results with available test results of the ship with the old propulsion group in earlier periods of ship operation. The results of measuring the basic maneuvering characteristics: ship speed, stopping distance and turning circle diameter, as well as propulsion characteristics: propeller shaft power, axial and torsional vibrations after six years of operation of the new propulsion confirmed all the advantages of diesel electric propulsion over classic diesel engine propulsion. However, certain problems have been noticed in terms of maintaining this complex plant, and proposed measures to overcome them.

On design of fatigue resistance metallic parts

This paper is devoted to design of metallic parts exposed to low cycle fatigue. Two flat discs, as representatives of these parts, were discussed. The first with 8, and the second with 64 eccentrically arranged holes. Their resistance to low cycle fatigue was investigated. Cyclic properties of two aerospace steels nominated for workmanship, plus planned revolves per minute and revolves per minute of 5% above planned, are taken into account. On the base of estimated low cycle fatigue life data, good design solution was discovered. On the other hand, it was shown that the both mentioned discs would have a large drop of resistance to low cycle fatigue for revolves per minute of 5% above planned.

Overview, analysis and research of the possibilities of application of new technologies in the process of demilitarization of the explosive ordnance

The classic methods of demilitarization of ordnance are high-risk operations, primarily for working personnel and operators, and then for the entire pyrotechnic security system. In addition to the security factors, high level of adverse effects of conventional demilitarization practices emits on the environment. Classical demilitarization procedures greatly limit the disassembly of ordnance due to outdated technology, so a large number of items are removed by the destruction process. The methods of destroying ordnance from the aspect of eco-system protection are completely unacceptable. The development and deployment of new technologies that are widespread in other fields today is an opportunity to solve key problems. In the field of unconventional processing procedures, water jet based technologies, which represent non-thermal methods, do not lead to thermal changes of the material during the process. An important factor in these technologies is that they are, as such, fully developed and known, with all the influencing factors that can be varied. For the application of this technology for the purposes of deliberation, existing systems need to be modified and aligned with the requirements of the deliberation process. Analyzing and reviewing existing research in the world, there is a trend towards the adoption of new and environmentally friendly technologies. With the development of new technologies, the assortment of ordnance has been expanded, reducing the need for destruction of these assets significantly. The main goal of this paper is to look at all influential factors that are critical in the process of disassembly using classical methods. Based on the identified critical factors in the area of classic deliberation processes, it is necessary to consider the possibility of applying new technologies in order to modernize the deliberation process and, above all, to make it safe and environmentally friendly.

Hybrid filament-wound materials: Tensile characteristics of (aramide fiber/glass fiber)-epoxy resins composite and (carbon fibers/glass fiber)-epoxy resins composites

In this paper a tensile characteristics of filament-wound glass fiber-aramid fiber/epoxy resins hybrid composites and glass fiber-two carbons fibers/epoxy resins hybrid composites are presented. Basic terms about hybride composite materials (origin, reasons for manufacturing, advantages, definitions, levels of hybridization, modes of classifications, types, categorization, and possible interactions between constituents) and used reinforcements and matrices are described. For a manufacturing of NOL rings four reinforcements (glass fiber, polyamide aromatic fiber and two carbon fibers) and two matrices (high and moderate temperature curing epoxy resin system) are used. Based on experimentally obtained results, it is concluded that hybride composite material consisting of carbon fiber T800 (67 % vol) and glass fiber GR600 (33 % vol) impregnated with epoxy resin system L20 has the highest both the tensile strength value and the specific tensile strength value. The two lowest values of both tensile strength and the specific tensile strength have hybrid material containing aramide fiber K49 (33 % vol) and glass fiber GR600 (67 % vol) and epoxy resin system 0164 and hybrid NOL ring with wound carbon fiber T300 (33 % vol) and glass fiber GR600 (67 % vol) impregnated with the same epoxy resin system. This investigation pointed out that increasing the volume content of aramide fiberK49, carbon fiber T300 and carbon fiber T800 in appropriate hybrid composites with glass fiber GR600 increases both the tensile strength value and the specific tensile strength value and decrease the density value, no matter the used epoxy resin system.