Issue 31

J.A.F.O. Correia et alii, Frattura ed Integrità Strutturale, 31 (2015) 80-96; DOI: 10.3221/IGF-ESIS.31.07 87 presents the experimental fatigue crack propagation rates obtained for the S355 steel, where stress ratio effects on fatigue crack propagation rates are shown. An increase in fatigue crack propagation rates is clear, when the stress ratio changes from 0 to any positive stress ratios considered in the experimental program. Also, it is clear that all the positive stress ratios resulted in similar crack propagation rates. This behaviour is consistent with a crack closure effect that occurs between R σ =0.0 and R σ =0.25. For R σ =0.0 there is some crack closure, the applied stress intensity factor range being not fully effective. For R σ =0.25 and higher, there is no crack closure, the applied stress intensity factor range being fully effective. Details about the properties evaluation for the S355 steel can be found in reference [19]. E [GPa] f u [MPa] f y [MPa] K’ [MPa] n’ 211.60 744.80 422.00 595.85 0.0757 Table 1: Monotonic and cyclic elastoplastic properties of the S355 mid steel.  ’ f [MPa] b  ’ f c 952.20 -0.0890 0.7371 -06640 Table 2: Morrow constants of the S355 mid steel.  K  [N.mm ‐1.5 ] da/dN  [mm/cycle] P‐00‐01 (R=0.0) P‐00‐03 (R=0.0) P‐25‐01 (R=0.25) P‐25‐02 (R=0.25) P‐05‐01 (R=0.5) P‐05‐02 (R=0.5) 1.0E‐6 1.0E‐4 400 500 1500 1.0E‐5 1.0E‐3 1000 1.0E‐2 Figure 5: Experimental fatigue crack propagation data of the S355 steel for distinct stress ratios: experimental results. 1.0E‐04 1.0E‐03 1.0E‐02 1.0E‐01 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+0 Cycles to failure, N f  /2  [‐] p=1% p=5% p=50% p=95% p=99% Experimental Data Postulated Data B = ‐3.2593 C = ‐9.1053 β = 4.6952 λ = 36.6676   = 5.8941 0.1 1 10 100 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+0 Cycles to failure, N f S WT  [MPa] p=1% p=5%  p=50% p=95% p=99% Experimental Data Postulated Data B = ‐4.1079 C = ‐4.4317 β = 3.6226 λ = 53.8423  = 7.2698 Figure 6: p-ε-N field for the S355 steel. Figure 7: p-SWT-N field for the S355 steel. The p-ε-N and p-SWT-N fields of the S355 steel are presented in Figs. 6 and 7, respectively. The constants of the Weibull fields are also referred in the figures. The extrapolations using the Weibull field should be avoided for high- and low-cycle fatigue lives. Since the number of cycles to fail the representative volume element, in the crack propagation regime, may