Issue 9

C. M. Sonsino, Frattura ed Integrità Strutturale, 9 (2009) 3-12; DOI: 10.3221/IGF-ESIS.09.01 10 Figure 15 : Application of the notch stress concept with r ref = 1.0 mm for the evaluation of welded K-nodes. The crack propagation lives, calculated as well as measured from a crack depth of a  1.00 mm to break-through, are presented in Fig. 16 . As the calculations were carried out with the Paris-Erdogan law for the probability of survival of P s = 50 %, Fig. 11, they are compared with the experimental mean curves. Here also, the calculations lie on the safe side. Besides this, they reveal that the cracks propagate slowly and permit their detection by inspections before break-through. Figure 16 : Comparison of experimental and calculated crack propagation lives. The accuracy of the concepts can be evaluated by the ratio between the calculated and experimental fatigue lives, Fig. 17 . On the basis of the assumptions and prerequisites described already, the hot-spot and crack-propagation concepts reveal the same accuracy. However, the notch stress concept with the reference radius r ref = 1.00 is more conservative. But this may result from the modelling of the weld. Also for the crack propagation concept, it has to be mentioned again that the crack propagation was calculated with R = 0 conservatively. Nevertheless, all three concepts do not exaggerate on the safe side and are reliable.