Issue 33

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 33 (2015) 335-344; DOI: 10.3221/IGF-ESIS.33.37 337 is introduced (Fig. 2). All tests are carried out with sinusoidal loading form, with load and torque moment control. For the simple cyclic tension fatigue tests, the specimens are tested with an applied maximum nominal stress equal to 80 MPa and with a frequency value 10 Hz. The combined tension/torsion tests are performed with the same stress ratio, applying synchronous and in-phase tensile and shear stresses whose maximum values are respectively equal to 75 and 59 MPa. Figure 2 : Test equipment for measuring COD and edge crack geometric parameters. a 0 /c 0 = 0.9 a 0 /c 0 = 0.37 a) b) c) Figure 3 : Aspect ratio versus crack depth under tension for different initial surface flaw geometries. a) b) c) Figure 4 : Surface crack paths under torsion for (a) transverse and (b,c) longitudinal initial notches .