The fatigue behaviour of 5 and 25 mm 5083 aluminium-alloy weldments

The fatigue behaviour of 5 mm and 25 mm aluminium-alloy butt weldments with full and incomplete penetration was investigated. Strain controlled fatigue tests of the 5083 aluminiu malloy base and 5183 weld metal were carried out to determine their cyclic material properties. Crack growth rate measurements were performed using center crack tension (CCT) specimens. The weldments with and without incomplete joint penetration (UP) were fatigue tested under constant amplitude axial loading for stress ratios of R = 0 and -1. For the same applied stress amplitude, it was found that the fatigue life of weldments under R = -1 is significant longer than under R = 0 due crack closure effects. The fatigue life of the weldments containing IJP was almost entirely devoted to crack gowth, while crack nucleation (and early growth) was found to be much more important for the butt weldments without IJP. It was found that the fatigue strength of the 5 mm weldments without IJP was not greater than that of t he 25 mm weldments without IJP as would have been expected for smaller size weldments. Estimates of angular distortions and calculations of induced bending stresses suggest that the performance of the 5 mm weldments is more affected by the bending stresses induced by weld distortions. The fatigue life of the tested specimens was predicted using an analytical model. A good agreement between the experimental and predicted fatigue lives was observed; and thus the analytical model was used to rationalize several experimental observations such as differing S-N diagram slopes for R = 0 and R = -1.