Original Article
Farhad Bagheroskouei
Abstract
Reliability assessment of power converters is extremely important due to the degradation of the converter performance under the thermal and electrical stresses. The space environment is one of the stressful environments for electronic components and equipment due to the range and high speed of temperature ...
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Reliability assessment of power converters is extremely important due to the degradation of the converter performance under the thermal and electrical stresses. The space environment is one of the stressful environments for electronic components and equipment due to the range and high speed of temperature changes.The normal or abnormal operation of a converter depends on the quality of the manufacturing process and the environmental and operating conditions. The failure indices usually are obtained based on the previous failures data which are calculated using the history of the main parameter of the converter. These indices are strongly influenced by the aging process. In this article, a new real-time indicator is introduced using the monitoring of the main parameters of the converter. The indicators are calculated using Replicator Neural Network (RNN). In fact, these indicators are obtained based on a comparison between a reference model of the converter in normal conditions and the estimation of abnormal operation of the converter in the future. In the proposed method, a normal distribution function is used to find the limits of error signals. The proposed method has several advantages such as considering all the uncertainties during the process of manufacturing the device, no need for the aging test data, and including all the failure types. In the Electrical power subsystem of a spacecraft, the reliability of power converters can be assessed based on the obtained data from the qualification models, benefiting the proposed method.
Original Article
Material science
Zahra Amirsardari; Babak Afzali; Mohammad Reza Amirsoleimani
Abstract
To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric conditions, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 15wt%, and 20wt% on gamma-alumina for decomposition of hydrazine. The performance of the catalysts was better ...
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To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric conditions, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 15wt%, and 20wt% on gamma-alumina for decomposition of hydrazine. The performance of the catalysts was better with 15wt% and 20wt% of the Ir nanoparticles, and also the selectivity to hydrogen was about 27%. An increase in the reaction rate from 181 h-1 to 218 h−1 was observed in the loading of 15% by weight of iridium particles due to the good dispersion of the active phases by preventing surface agglomeration. As a satisfactory result of this investigation, Ir catalysts with different weight percentage (15wt% and 20wt%) showed the same activity and selectivity, and are suitable substitutes for each other. Using a catalyst with a lower weight percentage of the active phase and high activity is economically acceptable due to its low cost.
Original Article
Material science
mojtaba forghani; Maedeh sadat Zoei; Mohammad Reza Pakmanesh; mohammad chiani; Saeed Asghari
Abstract
The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an ...
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The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an electrochemical process in which an oxide layer is formed using electricity. During the anodizing process, concentration polarization is created and the process is stopped when the limiting current resulting from the movement of electrical charges between the surface of the anodic layer and the electrolyte is increased. By stopping the process without spending enough time to obtain a thickness sufficient for colorability, a black anodic layer for use in space coatings is not obtained. In this research, by performing the anodizing process in four container of 250, 500, 2000 and 40000 cm3, the effect of the volume of the electrolyte on the wear and corrosion and optical-thermal properties of the layer obtained in each of the processes was investigated. The results showed that with the increase in the volume of the electrolyte caused by the increase in the volume of the container, the stopping time of the process increases. The evaluation of optical-thermal properties, wear resistance and corrosion resistance was done by infrared emission coefficient and solar absorption test, pin on disk test and salt spray test, respectively. The results of measuring optical-thermal and wear and corrosion properties for three container with volume of 500, 2000 and 40000 cm3 showed that with the increase in the volume of electrolyte and the process completion time of the process, the thickness of the anodic layer increased, which improved the optical-thermal properties, corrosion and wear resistance.
Original Article
Zahra Khaji; Mahdi Fakoor; Saeed Shakhesi
Abstract
The design of space operations must be done carefully. Because the smallest mistake in the design and construction of the spacecraft causes heavy financial losses. Electronic boards are one of the most important components of electronic systems in any operation. These boards must continue to operate ...
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The design of space operations must be done carefully. Because the smallest mistake in the design and construction of the spacecraft causes heavy financial losses. Electronic boards are one of the most important components of electronic systems in any operation. These boards must continue to operate under the applied loading. Strong levels of random vibrations can cause damage and fracture in electronic boards. The random vibration field applied to the electronic board can be modeled by mixed-mode I/II loading. Solder joints are very sensitive components of satellites. Fracture of electronic packages often occurs due to cracking in the joint between the electronic board and the solder under mixed-mode I/II loading. In this research, a new fracture criterion based on the maximum tangential stress is presented to predict the fracture for the interfacial crack between the electronic board and the solder. Based on the presented criterion, the direction and moment of crack initiation are predicted for the interfacial crack between isotropic and orthotropic materials. In this way, the fracture limit curve can be drawn. By comparing the presented criterion with the available experimental data, it can be concluded that the presented criterion has sufficient validity to evaluate the prediction of fracture in interfacial cracks between isotropic and orthotropic materials.
