Abstract: High-energy ball-milling in hexane medium was employed to prepare Nobel Zr-based bulk metallic glasses (BMGs) alloy of three different nominal compositions Zr47Be23Ni15Ti15, Zr50Be20Ni15Ti15 and Zr52Be18Ni15Ti15, numbers indicate at.%). The glass forming ability was found to increase with decreasing Zr and increasing Be content, which can be ascribed to the enhanced atomic size mismatch of the constituents on Be addition. Amorphous Zr47Be23Ni15Ti15 powder undergoes two-stage crystallization with onset temperatures at 640 and 700 K and glass transition temperature Tg at 566 K. In contrast, the Zr50Be20Ni15Ti15 and Zr52Be18Ni15Ti15 samples remained crystalline to a certain extent even after prolonged milling and contained FCC Zr crystallites. Structural characterization was done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, thermal analyses were performed by means of differential scanning calorimetry (DSC) thermogram to justify the experimental findings.
Abstract: The aim of this research is to investigate the effect of alloying elements of nickel, molybdenum, carbon and copper on hardness, density and microstructure of low alloy steel produced by powder metallurgy method. The results showed that molybdenum addition could lead to increase the density and hardness. Also, an increase in carbon content up to 1 wt. % could result in an increase in density and hardness. Copper is mainly added to increase strength as a result of solid solution hardening effect. Molybdenum is a ferrite stabilizer while Nickel is a strong austenite stabilizer. Consequently, the nickel and copper rich regions are mainly surrounded by austenite or bainite. Regions with higher amounts of alloying elements appeared to be martensitic islands. Increasing martensite and bainite volume fraction led to increase hardness.
Abstract: This review looks into the state of gigacycle fatigue behavior of some structural materials used in engineering works. Particular attention is given to the use of ultrasonic fatigue testing machine (USF-2000) due to its important role in conducting gigacycle fatigue tests. Gigacycle fatigue behavior of most materials used for very long life engineering applications is reviewed.Gigacycle fatigue behavior of magnesium alloys, aluminum alloys, titanium alloys, spheroid graphite cast iron, steels and nickel alloys are reviewed together with the examination of the most common material defects that initiate gigacycle fatigue failures in these materials. In addition, the stage-by-stage fatigue crack developments in the gigacycle regime are reviewed. This review is concluded by suggesting the directions for future works in gigacycle fatigue.
Abstract: The engineering parts joining by the spot welding require acceptable properties to survive the loading conditions XE "temperature". Several studies show that the welding variables have an effect on the properties of spot nugget XE "nugget" and on the future cracking. This review summarizes the resistance spot welding process (RSW). It introduces the basic spot welding principles, experiments XE"experiments" , limitation and defects XE "defects". The new concepts and awareness were presented. The results from the series of scientific works and literature are discussed. The metal’s weldability, XE "spotweldability" strength, XE"strength" and fracture are the main topics in several structural analysis. The welding variables effect on the mechanical properties and performance XE "mechanicalproperties" of the structures is the key analysis. In general, the increasing of the heat input by adjusting the current, time, and pressure producing higher weld area in turn enhance the toughness. However, by increasing the weld area, the defects and cracking tend to appear. Hence, a desired weld size with the mechanical properties is required. The nugget fracture mode is changing from plug or button tearing to shear failure mode depending on the weld properties. The crack grows either from the internal defects or around the nugget.
Abstract: An asymmetrical chiral metamaterial at microwave frequency is constructed by using four double-layered L-shaped strips which are rotated by 900 with respect to their adjacent metal strip. These different size strips allows another degree of freedom in the equalizing the orthogonal components of the electric fields at the output interface with 90o phase difference when the x-polarized wave excites the structure. The proposed structure exhibits the properties of chiral medium such as optical activity and circular dichroism. The L shaped chiral objects can be etched on double side substrate. The effect of structure on different electromagnetic parameter like chirality, optical activity and reflection characteristics are analyzed. Due to the strong chirality the structure posses negative refractive index for either left circularly or right circularly polarized wave. In this paper, a numerical study in the frequency domain of the electromagnetic-wave propagation through these types of structures is achieved by using the commercial software Computer Simulation Technology (CST) microwave studio.
Abstract: The present article describes the analysis of electromagnetic field in an induction MHD-stirrer for liquid metals with the account of transverse di-mensions of the inductor and bath with melt. The parameters of the equivalent circuit of a MHD-stirrer and its electromagnetic characteristics have been defined.
Abstract: Carbon/epoxy composite is one of the most useful polymer matrix composites that has special properties such as high strength-to-weight ratio, high hardness, high corrosion resistance, resistance to nuclear radiation and etc. has high consumption in different industries such as aerospace industry. Therefor loading monitoring of this type of composite is important. In order to determine various failure mechanisms, acoustic emission method has more performance than other non-destructive methods. In this research acoustic emission method was used to study carbon/epoxy composite and evaluate frequency range of flexural loading. For this purpose bending behavior of composite and relation between acoustic signals had studied. Using both fast Fourier transform and wavelet transform analysis methods in this research, led to the same result with margin of 5%. By using FFT analysis, maximum frequency of 135 KHZ was determined while using wavelet transform, this amount led to 142 KHz. Time limits that events was occurred on the specimen, monitored by online diagrams that obtained from acoustical system. Energy distribution at failure mechanisms was obtained as 17%, 29% and 48% related to matrix fracture, debonding and fiber breakage respectively. Finally failure mechanisms of composite were confirmed by SEM images. Energy distribution amounts, time limits and ascending progress of diagrams validate bending diagram.
Abstract: Heavy aircraft main landing gear tyres skid immediately after touchdown as result of the high slip ratio between the tyres and runway, which lead to tyre wear and smoke. In this paper, the tyre wear is modelled on the Archard theory using ANSYS mechanical transient, to reveal the wheel’s dynamic and the tyre tread wear. The wheel’s dynamic and the amount of wear are calculated for initially static and for pre-spun wheels in order to find the effectiveness of the technique of pre-spinning the wheel, as suggested by many patents since the early days of airplane use, in order to eliminate aircraft landing wear and smoke.
Abstract: In this paper, an unmanned aerial vehicle (UAV) with fixed-wing in normal condition flight, and fixed height, is considered and along with this process, kinematics model of UAV, assumed to have parametric uncertainty. In this situation the target of designing of proper controller family, based on switching logic, is to control the speed and roll angle of fixed-wing unmanned aerial vehicle in order to track desired path with minimum error. The desired path will be generated by trajectory maker block. The results of simulation on a fixed-wing UAV are presented to show the efficiency of the method.
Abstract: This article considers the problem of evaluating the effectiveness of energy-saving solutions in the aspect of the task to determine the timing of capital repairs of apartment buildings. The method of numerical simulation lifecycle of buildings is offered as a solution to this problem. It is proved that implementation of comprehensive overhauls of using energy-saving technologies increases the period of effective operation of the property as a whole, and in future - to lower operating costs. In order to enhance the safety of housing and improve the quality of housing, a new overhaul system of apartment buildings was adopted. Federal Law No. 271-FZ  obliges all the entities of the Russian Federation to adopt regional programs, which set deadlines of overhauls in all apartment houses. Analysis of the main program provisions showed that the overhaul term criteria do not include the results of monitoring the technical condition of buildings (physical deterioration of each component and engineering equipment), as well as the rate of the wear of building components by the time of repair and prediction of these indicators in the future during the lifecycle.