Effect of stress ratio on fatigue crack growth behaviour of friction stir welding between AA6061 and AA7075 alloys
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Date
2019-09
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
In the present work, fatigue crack growth in friction stir welded dissimilar AA6061 and AA7075 is performed under different stress ratio and maximum load condition. Crack is a damage that often occurs in members of structures and may cause sudden serious
failure of the structures. In a structure generally weld is the weakest section and therefore more prone to failure due to crack propagation. Therefore the study of mechanism of crack growth and its parameters is of paramount importance. The effects of presence of crack on fracture parameters like crack opening stress (Sop) and stress intensity factor (K) of specimen has been the subject of various investigations. However, the parametric studies like effect of stress ratio and amplitude; on the fracture parameters of specimen for friction stir welded joints has gaps in the literature and therefore needs further investigation.
Aluminium alloys AA6061 and AA7075 have been chosen for the present study as they are both used in conjunction in many areas of engineering such as marine and aircraft structures. The crack growth rate data for the weld shows that with the increase in stress
ratio, fatigue life of the joint decreases. The fatigue life obtained for constant maximum load and varying stress ratio condition shows that the highest Fatigue life is obtained for stress ratio R= -0.5 (48200 cycles) and lowest for R=0.8 (22200 cycles). The curve obtained using Newman equations is closer to plain strain condition. For the constant stress ratio and varying maximum load, it was observed that the fatigue life of joint decreases with the increase in applied maximum load (Pmax) with the highest fatigue life observed for Pmax=4kN (28908 cycles) and lowest for Pmax=6kN (21635 cycles).