Fatigue and fracture behaviour of Friction Stir Welded AA-2024-T351 joints

The presented paper deals with the mechanical properties of Friction Stir Welded (FSW) AA2024-T351-joints. The material's response to the static and fatigue strength (S-N curve) is summarised from previous work and referenced, while the testing methods and results for the fatigue and fracture mechanics' parameters regarding to the fatigue crack growth and occurrence of final fracture are discussed in the greater details and represent the main contribution of this work. The evaluation of the obtained experimental results was performed for three different welding speeds (v = 73, 116 and 150 mm/min), which enabled the determination of the most appropriate welding speed in regard to the fatigue and fracture behaviour of the analysed FSW-joint. The highest value of the threshold stress intensity factor range, Delta Kth, and, consequently, the highest resistance against crack extension, was obtained for the welding speed v = 116 mm/min. A similar conclusion was observed when determining the fracture toughness KJIc, where the highest value was obtained for the same welding speed. On the other hand, not significant differences in the slope m were obtained between the considered welding speeds when analysing the fatigue behaviour in the modified Paris diagram. In that respect, it can be concluded that the welding speed v = 116 mm/min is favourable in regard to the fatigue and fracture behaviour of the analysed FSW-joint.