Issue 48

C. Santus, Frattura ed Integrità Strutturale, 48 (2019) 442-450; DOI: 10.3221/IGF-ESIS.48.42 448 maximum normal stress amplitude σ n,a orientation, confirming the tensile type of this crack. However, the SWT parameter vanishes, since for this angle the maximum normal stress is zero, as evident in Fig. 6 (c). Figure 6 : (a) Crack evidence and initial orientation predictions for the as is series. (b) Stress analysis at the hot-spot, and (c) with the no fixed position Point Method. Figure 7 : (a) Crack evidence and initial orientation prediction for the Lubrication series. (b) Stress analysis with the no fixed position Point Method. (c) Repeated analysis with a lower FS material parameter. Figure 8 : (a) Crack evidence and initial orientation predictions for the Deep Rolling series. (b) Stress analysis with the no fixed position Point Method. Very shallow cracks were found for the Lubrication series with a clear inward direction, and without any apparent stage I to stage II transition. Again, the SWT and FS at the hot-spot predicted outward directions by considering the critical plane orientations where these two parameters are maximum, shown in Fig. 7 (b), and a similar conclusion was obtained with the fixed position PM described in Fig. 5 (a). However, by considering the implementation of the PM with no fixed evaluation point, as in Fig. 5 (b), the shear stress amplitude is very high for negative angles, while the maximum FS is still approximately perpendicular to the actual direction of the crack, due to the tensile maximum normal stress. A good correlation can thus be found if a lower value of the FS material parameter is assumed, such as k = 0.40, instead of the