Issue 33

A. Carpinteri et alii, Frattura ed Integrità Strutturale, 33 (2015) 376-381; DOI: 10.3221/IGF-ESIS.33.41 379 M M B  M T 8 90 30 R 45 12.7 30 Figure 1 : Fatigue tests on round specimens (10HNAP steel): torsion and bending. The 35 specimens tested under multiaxial loading are analysed in the following by employing the actual experimental loading histories, which are characterised by a sampling frequency of 266.67 Hz and a total duration of 184.32 s [12]. Then, the theoretical procedure presented in the previous Sections is applied to such experimental data, and the fatigue life cal T is computed. The comparisons between experimental data and theoretical evaluations are illustrated in Figs 2 and 3, where the solid line indicates cal T = T exp , the dashed lines correspond to / cal ex T T p equal to 0.5 and 2 , and the dash- dot lines correspond to / cal ex T T p equal to 0.3 and 3. A good agreement for the fatigue loading examined can be observed. T cal , [cycles] T exp , [cycles] 10 5 10 4 10 2 10 6 10 7 10 2 10 3 10 4 10 5 10 6  =   8 10 3 10 7 T cal , [cycles] T exp , [cycles] 10 5 10 4 10 2 10 6 10 7 10 2 10 3 10 4 10 5 10 6  =   4 10 3 10 7 Figure 2 : Comparison between experimental and theoretical fatigue lives ( / 8    ). Figure 3 : Comparison between experimental and theoretical fatigue lives ( / 4    ). The comparisons presented in Figs 2 and 3 seem to be quite satisfactory, with 63% of the fatigue life calculation results included into the scatter band with coefficient 2, whereas 66% of such results are included into the scatter band with coefficient 3. The theoretical results based on the frequency domain approach are also compared with those determined by the time- domain criterion proposed in Ref. [4] (Figs 4-5). Note that the results here presented based on the time-domain criterion (based on a non-linear damage accumulation rule) are slightly different from those shown in Ref. [4], due to the different value adopted for the normal stress fatigue limit (in Ref. [4], af  = 225.0 MPa related to push-pull loading was adopted).