A 3-D upper-mantle structure beneath Turkey is investigated using phase speeds of fundamental-mode Rayleigh waves employing a conventional two-station method with high-density seismic networks in Turkey. We analyse 289 seismic events with moment magnitude 5.5 and greater, and with focal depth shallower than 100 km between 2006 and 2008. Waveform data are derived from 164 three-component broad-band seismic stations operated by two national seismic networks. At first, Rayleigh-wave phase speed maps are obtained from the inversion of two-station phase speeds using about 1000–3000 paths, depending on the period of Rayleigh waves. The three-dimensional S-wave model is then obtained in the depth range from 40 to 180 km using the phase speed maps in the period range from 25 to 120 s. Our model reveals the fast anomalies in the north of Cyprus associated with the subducted portion of the African oceanic lithosphere from the Cyprus trench. We identify a vertical discontinuity of the fast anomaly associated with the Cyprus slab starting at 60–80 km depth which may represent a minor tear of the Cyprus slab. We observed that the western part of the Cyprus slab is getting closer to the edge of the Hellenic slab beneath the Isparta Angle (IA) and Antalya Basin. Our model also indicates a slow wave speed anomaly beneath the IA and Antalya Basin probably due to hot materials of asthenosphere rising from a tear of the subducted African oceanic lithosphere; that is, a slab tear between the Cyprus and the Hellenic subductions. In the eastern part of Turkey, a widespread slow anomaly appears in the model that corresponds to the Eastern Anatolian Accretionary Complex (EAAC). Our model shows a fast anomaly beneath the EAAC that can be interpreted as the detached portion of the subducted Arabian lithosphere
Friction stir welding (FSW) between 2 mm thickness AA 5754 aluminum alloy sheet was researched in the current research. The welded joints were qualified by its aspects, microstructural ,mechanical features and corrosion behavior at cell temperature. The effect of the conical tool geometry on the FSW AA5754 are investigated over potentiodynamic polarization, open circuit potential (OCP) monitoring, test of the susceptibility to corrosion, micro-hardness and tension tests. The thermomechanically affected zones adjacent to weld nugget are most susceptible to corrosion in the weld joints. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses on the stir zone suggested that, intermetallic phases of the base material were mechanically fractured, smeared and mixed to different geometries due to tool stirring. The increase in anodic reactivity in the weld zone was due to the sensitisation of the grain boundaries leading to intergranular attack. Enhancement of cathodic reactivity was also found in the nugget as a result of the precipitation of Mgrich phases.
In this study, the fatigue strength of AISI 430-304 stainless steels welded by CO 2 laser beam welding (LBW) is investigated. Laser welding experiments are carried under helium atmosphere at 2000, 2250 and 2500 W welding powers with 100 cm/min welding speed. The welding zones are examined by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy analysis. Fatigue tests are performed using an axial fatigue test machine, and the fatigue strength is analysed drawing S-N curves and critically observing fatigue fracture surfaces of the tested samples. The experimental results indicate that mechanical properties and microstructural features are affected significantly by welding power. The fatigue strength of CO 2 laser welded samples increase due to higher deep penetration in welding zone with increasing welding power in chosen conditions. The best properties are observed with the specimens welded at 2500 W heat input and 100 cm/min welding speed.В цій роботі досліджено втомну міцність неіржавійних сталей AISI 430-304, зварених променем CO 2 -лазера. Експерименти з лазерного зварюван-ня виконувалися в атмосфері гелію за потужности зварювання у 2000, 2250 і 2500 Вт із швидкістю зварювання у 100 см/хв. Зони зварювання досліджувалися методами оптичної мікроскопії, сканівної електронної мікроскопії та енергодисперсійної спектроскопії. Дослідження на втому виконувалися з використанням машини для випробувань на вісну втому, а втомна міцність аналізувалася шляхом побудови S-N-кривих та крити- U. CALIGULU, M. TURKMEN, A. OZER, M. TASKIN, and M. OZERчного спостереження поверхонь втомного руйнування досліджених зраз-ків. Експериментальні результати показують, що механічні властивості та мікроструктурні особливості значно залежать від потужности зварю-вання. Втомна міцність зразків, зварених CO 2 -лазером, зростає завдяки збільшенню глибини проникнення в зоні зварювання зі збільшенням по-тужности зварювання за обраних умов. Найкращі властивості спостеріга-лися у зразків, зварених за підведеної теплоти при 2500 Вт та швидкости зварювання у 100 см/хв.В данной работе исследована усталостная прочность нержавеющих сталей AISI 430-304, сваренных лучом CO 2 -лазера. Эксперименты по лазерной сварке выполнялись в атмосфере гелия при мощностях сварки 2000, 2250 и 2500 Вт и скорости сварки 100 см/мин. Зоны сварки исследовались ме-тодами оптической микроскопии, сканирующей электронной микроско-пии и энергодисперсионной спектроскопии. Испытания на усталость про-изводились с использованием машины для испытаний на осевую уста-лость, а усталостная прочность анализировалась путём построения S-N-кривых и критического наблюдения поверхностей усталостного разруше-ния исследованных образцов. Экспериментальные результаты показыва-ют, что механические свойства и микроструктурные особенности значи-тельно зависят от мощности сварки. Усталостная прочность образцов, сваренных CO 2 -лазером, возрастает благодаря увеличению глубины про-никновения в зоне сварки с увеличением мощности сварки при выбран-ных условиях. Наилучшие св...
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