Fabrication, characterization, and mechanical properties of spark plasma sintered Al-BN nanoparticle composites

International audienceFabrication of high strength yet light and low cost composite materials with good mechanical properties at room and elevated temperatures is a challenge that metallurgy and materials science communities are facing for many years, and no "dream material" has been developed so far. The primary goal of this study was to fabricate, characterize, and to carry out tensile tests on Al-based composite materials strengthened with commercially-available BN nanoparticles (BNNPs). The composites were fabricated by spark plasma sintering (SPS) technique. The structures of powder mixtures and composite materials, as well as their fracture surfaces, were studied by scanning and transmission electron microscopy. The influence of BNNPs content (0.5, 1.5, 3, 4.5, 6, and 7.5. wt%) and holding times (5, 60, and 300. min) at 600. °C during SPS on the tensile strength was investigated. A maximum increase in strength was observed for Al-based composites with 4.5. wt% of BNNPs. The sample demonstrated a 50% increase in tensile strength compared with pristine Al. Although the tensile tests performed at 300. °C revealed that the tensile strength became 20% lower than the strength at room temperature, it was, however, still 75% higher compared with that of the pure Al at 300. °C. In addition, at 300. °C the Al-BNNPs composites demonstrated a much higher value of yield stress, about 115. MPa, which is 190% higher than that of pure Al at the same temperature. The damping properties of Al-BNNPs composites were evaluated by temperature dependent internal friction (TDIF) measurements. The obtained results are discussed based on structural analysis and the TDIF data. © 2015 Elsevier B.V

Fabrication, characterization, and mechanical properties of spark plasma sintered Al-BN nanoparticle composites

International audienceFabrication of high strength yet light and low cost composite materials with good mechanical properties at room and elevated temperatures is a challenge that metallurgy and materials science communities are facing for many years, and no "dream material" has been developed so far. The primary goal of this study was to fabricate, characterize, and to carry out tensile tests on Al-based composite materials strengthened with commercially-available BN nanoparticles (BNNPs). The composites were fabricated by spark plasma sintering (SPS) technique. The structures of powder mixtures and composite materials, as well as their fracture surfaces, were studied by scanning and transmission electron microscopy. The influence of BNNPs content (0.5, 1.5, 3, 4.5, 6, and 7.5. wt%) and holding times (5, 60, and 300. min) at 600. °C during SPS on the tensile strength was investigated. A maximum increase in strength was observed for Al-based composites with 4.5. wt% of BNNPs. The sample demonstrated a 50% increase in tensile strength compared with pristine Al. Although the tensile tests performed at 300. °C revealed that the tensile strength became 20% lower than the strength at room temperature, it was, however, still 75% higher compared with that of the pure Al at 300. °C. In addition, at 300. °C the Al-BNNPs composites demonstrated a much higher value of yield stress, about 115. MPa, which is 190% higher than that of pure Al at the same temperature. The damping properties of Al-BNNPs composites were evaluated by temperature dependent internal friction (TDIF) measurements. The obtained results are discussed based on structural analysis and the TDIF data. © 2015 Elsevier B.V

Compensate for amplitude fault radiators in the planar phased array antenna

Приведен метод адаптации плоской фазированной антенной решетки к амплитудным отказам с использованием предложенной методики моделирование отказовых ситуаций в линейной решетке. Путем анализа результатов моделирования сформулированы возможности предложенной методики. Показано, что в результате применения предложенной методики при использовании её в плоской фазированной антенной решетке можно получить оптимальную (желаемую) диаграмму направленности в плоскости адаптации, при этом показано, что в ортогональной плоскости диаграмма направленности остается неизменной и ровной искаженной. Показано преимущество адаптации в эквивалентных линейных ФАР.Наведено методику організація адаптації плоскої фазованої антенної решітки (ФАР) до амплітудних відмов. Показано перевагу адаптації в еквівалентних лінійних ФАР.The technique of adapting the organization flat phased array antenna (PAR) to amplitude failures. The advantage of the adaptation of the equivalent linear phased arra

A method of diagnostics of phased array antenna is in the field terms

Рассматривается метод диагностики фазированной антенной решетки, реализуемый из ближней зоны антенны на месте её базирования в полевых условиях, позволяющий исключить влияние эхо-сигналов на результаты диагностики. приведена структурная схема измерительно-вычислительной системы встроенного контроля фазированной антенной решетки реализующая метод дискретного преобразования Уолша и рассмотрена в полевых условиях. При этом рассмотрена возможность реализации в представленной системе методы дискретного преобразования Уолша применительно к случаю, когда на измерительной площадке присутствуют эхо-сигналы и возможны ошибки в позиционировании измерительного зонда.Розглядається метод діагностики фазованих антенних решіток , що реалізовується з ближньої зони антени на місці її базування в польових умовах, дозволяє виключити вплив луна-сигналів на результати діагностики. приведена структурна схема вимірник обчислювальної системи вбудованого контролю фазованих антенних решіток, що реалізовує метод дискретного перетворення Уолша і розглянута в польових умовах. При цьому розглянута можливість реалізації в представленій системі методи дискретного перетворення Уолша стосовно випадку, коли на вимірювальному майданчику присутні луна-сигнали і можливі помилки в позиціонуванні вимірювального зонда.The method of diagnostics of phased array, realized from the near area of aerial in place of its basing in the field terms, allowing to eliminate influence of echo signal on the results of diagnostics, is examined. the flow diagram of the measuring computer system of built-in control of phased array is resulted realizing the method of discrete transformation of Walsh and considered in the field terms. Marketability is thus considered in the presented system methods of discrete transformation of Walsh as it applies to a case, when on a measuring ground echo signal is present and errors are possible in keeping of measuring probe