Issue 35

S. Xinhong et alii, Frattura ed Integrità Strutturale, 35 (2016) 441-448; DOI: 10.3221/IGF-ESIS.35.50 446 Orientation predictions of different approach The comparison of measured crack angle with the predictions based on the maximum shear stress amplitude[7], Findley parameter[8] and Fatemi-Socie parameter [9] for different mean stresses is shown in Fig.8. The abscissa represents the specimen, and vertical coordinates represent the value of measured angle. Black solid round dots are representative of measured angles. Hollow dots, triangles and squares are representative of the predicted angles based on the maximum shear stress amplitude, Findley parameter and Fatemi-Socie parameter, respectively. 、 (a) Tension-torsion fatigue for ,  x m =0MPa. (b) Tension-torsion fatigue for ,  x m =50MPa. (c) Tension-torsion fatigue for ,  x m =100MPa. (d) Tension-torsion fatigue for ,  x m =150MPa. Fig.8.Comparison of measured crack angle with the predictions for different mean stresses The measured angles and predicted angles based on three parameters under tension-torsion loading for ,  x m =0MPa are shown in Fig. 8(a). There are three groups of different axial amplitudes but the axial mean stress and torsion stress are all the same. Although there are two equal values of maximum shear stress amplitude planes and the normal mean stress on both planes is zero, all of the measured angles are in the side of the maximum shear stress plane, which direction is nearly 80 ° apart with the direction of specimen axial. Most of the measured angles are larger several degrees than the predictions made by the maximum shear stress amplitude. All the predictions made by Findley parameter and Fatemi-Socie parameter are smaller several degrees than the predicted value by the maximum shear stress amplitude. The measured angles and predicted angles based on three parameters under tension-torsion loading for ,  x m =50MPa are shown in Fig. 8(b). There is normal mean stress on both the maximum shear stress amplitude planes, and the value of normal mean stress is larger on the plane which direction is around -15°. But all of the measured angles are still in the side of the maximum shear stress plane with smaller normal mean stress. All the predictions made by Findley parameter and Fatemi-Socie parameter are in the side of the maximum shear stress plane with larger normal mean stress. And their values are nearly 5 ° smaller than the predictions made by the maximum shear stress amplitude. The measured angles and predicted angles based on three parameters under tension-torsion loading for ,  x m =100MPa are shown in Fig. 8(c). Most of the measured angles are in the side of the maximum shear stress amplitude plane with larger normal mean stress, which direction is close to perpendicular to the specimen axis. The difference between most of measured angles and hollow dots corresponding to the maximum shear stress amplitude is 5 ° or more. Only three