Issue 33

F. Berto et alii, Frattura ed Integrità Strutturale, 33 (2015) 229-237; DOI: 10.3221/IGF-ESIS.33.29 235       1 3 2 2 2 2 3 1 1 3 2 1 2 1 1c 3c 2 1 nom W nom W W c un notched specimens pure tension E SED c un notched specimens pure torsion E c K K e e V notched specimens multiaxial loading E R R                                        (11) Fig. 3 shows the synthesis in terms of SED of all the fatigue strength data presented in this contribution is shown. Again two different control radii equal to R 1c = 0.051 mm and R 3c = 0.837 mm respectively have been adopted. The scatterband includes all the data from un-notched and V-notched specimens under pure tension, pure torsion and multiaxial loading, regardless of the load ratio and the phase angle. It is also characterized by an inverse slope k equal to 5.90, a scatter index T W = 2.5 and a value of the strain energy density at the reference number of cycles, N A = 2·10 6 , that equals 3.08 MJ/m 3 . The equivalent stress-based scatter index T  results to be 1.58, that is comparable with that observed in the Haibach scatterband (T   = 1.50). Figure 3 : Synthesis by means of local SED of un-notched and V-notched specimens data. C ONCLUSIONS large bulk of fatigue strength data referred to cylindrical V-notched specimens made of titanium grade 5 alloy (Ti-6Al-4V) and tested under combined tension and torsion loading, both in-phase and out-of-phase, have been analysed together with those obtained from un-notched and V-notched specimens under pure tension and pure torsion loading. A total of over 160 new fatigue data (15 Wöhler curves) have been summarised in the present work. All fatigue strength data from uniaxial and multiaxial tests have been presented first in terms of nominal stress amplitudes referred to the net area and then reanalysed in terms of the local strain energy density averaged over a control volume that embraces the V- notch tip. The dependence of the control radius by the loading mode is analysed showing the need to use, for the titanium alloy Ti-6Al-4V, a different size of the control volume under tension and under torsion. The synthesis based on the local strain energy density allows us to obtain a quite narrow scatter-band, which has a scatter index equal to 2.50, considering all the data from V-notched and smooth specimens under pure tension, pure torsion and multiaxial loading, independent of the load ratio and the phase angle. A