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In the last period of the Umayyads, some clerks of mawālī origin began to have a voice in the administration and to draw attention to their intellectual aspects. These people, culturally equipped and experienced in administrative life, provided the emergence of the adīb (enlighted writer/man of letters) bureaucrat typology in the Islamic world. One of them, ʿUmāra b. Ḥamza (d. 199/814-15 [?]) came forward as a high-level clerk and statesman during the establishment years of the Abbasids. ʿUmāra has an extremely arrogant aspect, which was the subject of idioms. The Abbasid caliphs put up with this feature because of his usefulness and ability. ʿUmāra’s official and personal letters were highly appreciated; for this reason, he was mentioned among the top ten masters of eloquence in the 3-4th/9-10th century of the Islamic world. Many anecdotes have been recorded about him due to the various events he experienced as a clerk, tax administrator, governor and diplomat, and his interesting personality. Issues such as being a mawālī, being accused of zindīq, ungrateful attitudes towards the caliphs, haughty attitude, wealth, generosity, his duties such as being an ambassador to Byzantium, and the nature of his writings shed light on the first period of the Abbasids in many ways. In this article, ʿUmāra b. Ḥamza’s life and personality are discussed, together with the conditions of the period and prominent figures. In addition, the position and activity of the mawālī class in the early Abbasid period are explained through the example of ʿUmāra. [ABSTRACT FROM AUTHOR]

Friction drilling is an important non-traditional manufacturing method with the effect of heat caused by friction on a work piece-tool interface with a rotating tool. The purpose of this method is to increase the length of the connection through the bushing formed in the lower part of the hole in the thin-walled sheets. In this study, it is aimed to investigate the effects of material thickness and tool diameter on bushing height (ha), bushing wall thickness (hç) and micro hardness change in friction drilling method. In experiment studies, tungsten carbide (WC) tools were used with taper angle of φ=36°, the tool diameters of Ød=5 mm, Ød=10 mm, Ød=15 mm and Ød=20 mm. Friction drilling was applied to St37 steel with a thickness of t=2 mm, t=4 mm, t=6 mm, t=8 mm and t=10 mm. The experiments were carried out at a speed of n=1120 rpm and a feed rate of f=25 mm/min. The effects of material thickness and tool diameter on bushing height, bushing outer diameter, bushing shapes and changes in micro hardness were investigated. The largest bushing height of ha=15.30 mm, the lowest bushing wall thickness of hç=4.25 mm and the highest micro hardness of 183 HV was obtained. It was observed that material thickness and tool diameter had a significant effect on bushing wall thickness and bushing height, but micro hardness values did not change much. [ABSTRACT FROM AUTHOR]