Issue 35

S. Xinhong et alii, Frattura ed Integrità Strutturale, 35 (2016) 441-448; DOI: 10.3221/IGF-ESIS.35.50 443 direction of the specimen and the direction normal to the crack initiation and early propagation plane is defined as critical plane orientation, φ , which is shown in Fig. 2, where the origin O of the coordinate system is at the surface of the minimum diameter dimension of specimen, the x direction is the longitudinal direction of the specimen and the y direction is the direction circumferential to the surface of the specimen. Figure 2 : Definition of the crack initiation and early propagation plane orientation  The crack path under different mean stress is shown in Fig.3. The position of the crack initiation and early propagation plane orientation is marked in the figure. (a) ,  x m =0MPa, ,  x a =185 MPa (b) ,  x m = 50MPa, ,  x a =185 MPa (c) ,  x m = 100MPa, ,  x a =180 MPa (d) ,  x m = 150MPa, ,  x a =140 MPa Figure 3 : crack path under different mean stress. X X X X