Fatigue Tests of Notched Specimens Made from Butt Joints at Steel

The weld toe as well as the weld root of joints acts as a geometrical notch, which decreases the fatigue strength of welded components. Local approaches used for fatigue assessment account for the local stress concentration when referring to the notch stress as a fatigue parameter. This applies also to the approaches based on the notch stress intensity factor like, for example, the averaged strain energy density, neglecting the actual notch radius and considering a sharp notch as a simplification. A uniform S-N curve valid for different types of welded joints and failure locations was derived from re-analyses of fatigue test results as documented in literature. The fatigue tests described in this paper aimed at validating that energy-based S-N curve by dedicated tests on artificially notched specimens. At first, four parameters were investigated in order to estimate their influence on the fatigue strength and to select appropriate notch geometries for the final step of the test campaign. The advantages of these tests are that both the exact notch geometry and the local stress range at the notch, including misalignment effects, were identified and considered in experimental data analysis. This paper presents the results of the rather comprehensive testing activities and comparisons with the design-S-N curve mentioned, yielding unexpected fatigue behaviour. This can be explained by the short crack propagation life