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كلال الدورات المنخفضة في سبيكة المنيوم قابلة للتصليد بالترسيب == Low Cycle Fatigue of Precipitation Hardened Aluminum Alloy

اسم المؤلف: سيف خالد محمود

اسم المشرف: ظافر صادق الفتال

الموضوع العام: هندسة الميكانيك

السنة: 2014

الموضوع الدقيق: ميكانيك تطبيقي

الدرجة: ماجستير

الجامعة: الجامعة التكنولوجية - قسم الهندسة الميكانيكية

اللغة: الانكليزية

مكان الجامعة: بغداد

الصفحات الاولى:

المستخلص: لسبائك الالمنيوم عالية المقاومة طيف واسع من التطبيقات من صناعة السيا ا رت الى الصناعات الفضائية.ان السبب الرئيسي وراء النمو السريع للطلب على هذة السبائك هو مزيج من الخواص الفريدة التي جعلت منها واحدة من اكثر الت ا ركيب والمواد الهندسية استعمالا، ولذلك ل | High strength AL - alloys have a wide spectrum of applications from automobile to aerospace industries. The demand for these aluminum alloys grows rapidly because of the unique combination of properties which make them the most versatile of engineering and construction materials. Hence, development of high strength Al - alloys continues to be an important area of research.In this work, the influence of different heat treatments on the mechanical properties and fatigue life under low cycles of wrought 7075 aluminum alloy was experimentally investigated. The heat treatments included peak ageing (T6), over ageing (T73) and annealing (O).The effect of heat treatments on the alloy was explained in terms of their influence on the mechanical properties. The results showed that T73 temper has an ultimate strength of 504.7 MPa and elongation of 12.5%. Peak ageing treatment enhanced the strength by 10.9% and reduced the elongation by 7.2%, while in the annealed condition, the strength was reduced and the elongation was improved by 51.33% and 31.2%, respectively. T6 had the highest hardness followed by T73 and O tempers.The flat fatigue specimens were subjected to constant reverse bending load. The tests were performed at the laboratory environment with a frequency of 23.3 Hz and at a stress ratio (R) of - 1. For each temper, strain - life graphs were obtained for specimens with notches in the form of central cylindrical holes made by drilling. The fatigue resistance of specimens with notches was compared to the results for notch - free specimens. It was observed that the presence of a stress raiser, such as a drilled hole, lowers the fatigue life for all tempers. However, the notch sensitivity of the fatigue life was different for each temper.The fatigue crack growth rate of T73 and annealed temper was investigated, the results showed that T73 treated sample exhibits higher crack growth resistance. Paris` equation was derived for each temper Keywords : LCF. precipitation hardening. 7075 aluminum alloy. fatigue crack growth.