Issue 46

A. Deliou et alii, Frattura ed Integrità Strutturale, 46 (2018) 306-318; DOI: 10.3221/IGF-ESIS.46.28 312 Figure 9: Evolution of the crack length according to the number of cycles. In order to explore the field of medium and high cracking rates, we imposed a sinusoidal load of constant amplitude 7 P KN   for the duration of the test, with a load ratio 0.1 R  . The curves of evolution of the length of the crack “ a ” as a function of number of cycles of BM, WM and HAZ regions of welded joint are presented in Fig 9. The difference in advanced of the crack between these curves in higher as the number of cycles increases. These results influenced on the evolution of the nominal cracking rate versus plotted on a bi- logarithmic curve shown in Fig. 10. Values of da dN are between 10 -6 and 10 -2 mm/cycle and the values of K  values change from: - 13.8 to 36.9 MPa m in the heat affected zone. - 13.2 to 36.6 MPa m in the weld metal. - 11.7 to 35.4 MPa m in the base metal. The curves have an almost rectilinear look on a big part of the explorer domain, which can be presented a law of Paris of the form [46]:   m da C K dN   (4) The results of the fatigue tests obtained in the three zones recorded respectively in Tab. 6. Table 6: Paris law in the different zones studied. Regions Paris law BM   4.87   11 1.1  da E K dN    WM   4.55   11 5.2  da E K dN    HAZ   3.82   11 8.1  da E K dN   