Issue 41

F. Berto et alii, Frattura ed Integrità Strutturale, 41 (2017) 79-89; DOI: 10.3221/IGF-ESIS.41.12 87 Fig. 5 reports the synthesis of all experimental fatigue results analysed in the present contribution by means of the averaged SED. The control radius R 1 = 0.051 mm has been adopted to evaluate the SED contribution due to tension loading, while the control radius R 3 = 0.837 mm has been employed for the SED contribution due to torsion loading. All fatigue strength results relevant to smooth and notched samples under pure tension, pure torsion and multiaxial loading conditions are included in the obtained scatter band, independently of the nominal load ratio and of the phase angle. The design scatter band is characterized by an inverse slope k of 5.90, by an energy-based scatter index T W = 2.50 and by a SED value at N A = 2·10 6 cycles equal to 3.08 MJ/m 3 . However, the equivalent stress-based scatter index, that is T  = (T W ) 0.5 , equals 1.58, which is very similar to that of the Haibach scatter band (T   = 1.50). Figure 5 : Local SED-based synthesis of experimental fatigue results relevant to smooth and sharply notched specimens. Almost 250 fatigue data are summarised in the scatter band. C ONCLUSIONS large bulk of experimental fatigue results relevant to axisymmetric notched samples subjected to multiaxial loadings, both proportional and non-proportional, have been re-analysed and compared with the fatigue strength data relevant to smooth and notched samples subjected to pure tension and pure torsion loadings. All specimens were made of titanium grade 5 alloy (Ti-6Al-4V). Altogether, more than 250 fatigue results, corresponding to 19 S-N curves, have been analysed in this contribution. First, the experimental results obtained from uniaxial and multiaxial fatigue tests have been examined on the basis of nominal stress amplitudes. Then, they have been re-analysed by means of the linear elastic strain energy density (SED) averaged over a control volume surrounding the notch root. The effect of the loading mode on the control volume size has been analysed in detail, showing that different control radii must be adopted under tension and torsion loading conditions, dealing with notched components made of Ti-6Al-4V titanium alloy. The averaged SED-based synthesis enables to obtain a quite narrow scatter band, characterized by an energy-based scatter index of 2.50. In particular, the fatigue design scatter band was derived by taking into account all experimental results 0.2 2 20 1.0E+04 1.0E+05 1.0E+06 1.0E+07 Strain energy density range,  W, [MJ/m 3 ] Number of cycles to failure, N Tension, R=-1 Tension, R=-1 Torsion, -3 ≤ R ≤ 0.5 Torsion, -1 ≤ R ≤ 0.5 Multiaxial, R=-1, in-phase Multiaxial, R=-1, in-phase Multiaxial, R=0, in-phase Multiaxial, R=-1, out-of-phase Multiaxial, R=-1, out-of-phase Multiaxial, R=0, in-phase Multiaxial, R=0, out-of-phase Multiaxial, R=0, out-of-phase Un-notched specimens k=5.90 SED range (2x10 6 , P.s. 50%)= 3.08 MJ/m 3 T W =2.5 Ti6Al4V 251 data R 1 = 0.051 mm R 3 = 0.837 mm V-notched specimens V-notched specimens  = 0.6  = 2.0 A