Issue 37

F. Berto et alii, Frattura ed Integrità Strutturale, 37 (2017) 69-79; DOI: 10.3221/IGF-ESIS.37.10 77 The parameter c w equals 1.0 in the case R = 0, while it results equal to 0.5 for R = -1. By adopting the coefficient c w , the closed-form expressions to evaluate the averaged SED, related to smooth samples (Eqs. (1, 2)) and to components weakened by sharp notches (Eq. (8)), become as follow:                                      loading multiaxial specimens notched V R K e R K e E c torsion pure specimens notched un E 1 c tension pure specimens notched un E2 c SED 3 1 12 3 2 3 3 12 1 2 1 1 W 2 nom W 2 nom W (11) 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). It should be noted that an extensive review of the considered experimental results will be carried out in the special issue dedicated to the 11th International Conference on Multiaxial Fatigue and Fracture (ICMFF11) [32]. 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. 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