Issue 13

F. Iacoviello et alii, Frattura ed Integrità Strutturale, 13 (2010) 3-16; DOI: 10.3221/IGF-ESIS.13.01 9 Ferrite and cementite lamellae are not necessarly a preferential propagation path for the fatigue crack (Fig. 24, 25, 26) , also if pearlite lamellae and crack path are almost paralel. Secondary cracks are less frequent if compared to ferritic DCI (Fig. 27), with a really reduced path. Nearby the fatigue crack, graphite nodules are characterized by the presence of secondary crack inside the nodule (Fig. 28). Ferritic-pearlitic DCI GJS500-7 crack paths are characterized by the presence of many secondary cracks that initiate from the main fatigue crack path (as in the ferritic DCI , Fig. 29) and by the presence of a “clean” graphite elements - matrix debonding (as in the pearlitic DCI, Fig 30, 31, 32). Figure 19 : Ferritic DCI (R = 0.5,  K = 13 MPa√m). Figure 20 : Ferritic DCI (R = 0.5,  K = 18 MPa√m). Figure 21 : Pearlitic DCI (R = 0.1,  K = 13 MPa√m). Figure 22 : Pearlitic DCI (R = 0.1,  K = 15 MPa√m). Figure 23: Pearlitic DCI (R = 0.5,  K = 10 MPa√m). Figure 24 : Pearlitic DCI (R = 0.75,  K = 7 MPa√m). Figure 25 : Pearlitic DCI (R = 0.1,  K = 12 MPa√m). Figure 26 : Pearlitic DCI (R = 0.75,  K = 8 MPa√m). Figure 27 : Pearlitic DCI (R = 0.1,  K = 11.5 MPa√m). Figure 28 : Pearlitic DCI (about 30  m from the crack). Figure 29 : Ferritic-pearlitic DCI GJS500-7 (R = 0.75,  K = 6 MPa√m). Figure 30 : Ferritic-pearlitic DCI GJS500-7 (R = 0.1,  K = 10 MPa√m). Figure 31 : Ferritic-pearlitic DCI GJS500-7 (R = 0. 5,  K = 8 MPa√m). Figure 32 : Ferritic-pearlitic DCI GJS500-7 (R = 0.75,  K = 8 MPa√m).