Gope, P.C.Joshi, Ayush2019-12-102019-12-102019-08http://krishikosh.egranth.ac.in/handle/1/5810137232Aluminum 7075-T651 is one of the widely used materials for various applications in industry, aerospace, utensils, etc. In the present investigation, fatigue crack growth experiments were performed on both friction stir welded CT specimen and base material CT specimen that are naturally aged, artificially aged at 1900C for 24 h (HT1) and 4230C for 12 h (HT2) with Pmax= 5 kN, Pmin= 0.5 kN and frequency of 6 Hz with R=0.1 under constant amplitude loading and under single overload with an overload ratio of 1.8. The experimental data obtained has been used to plot a-N and da/dN vs. 􀀧K curve and various fatigue crack growth parameters such as Paris crack growth constants, crack opening stress intensity factor, etc. are determined. The fatigue life is found to be 39000, 36500, 31000 and 41000, 37500, 34000 cycles, respectively for friction stir welded CT specimen and base material CT specimen that are naturally aged, HT1 and HT2.It is observed that there is a significant variation in the variances of crack length increment after the overload. The reduction of crack growth rate is noticed due to the application of overload with an overload ratio of 1.8.The fatigue life after the single overload is found to be 49000, 45000, 40000 and 53000, 46000,41000 cycles, respectively for friction stir welded CT specimen and base material CT specimen that are naturally aged, HT1 and HT2. The values of material constants C and m are calculated through single Paris Curve fit. Scanning electron microscope (SEM)study of fracture surface at different locations is carried out to investigate different modes of fracture occurred to present the effect of different heat treatments such as natural ageing, artificial ageing HT1 and HT2 under constant amplitude loading and due to single overload.ennullThesis