Issue 31

J.A.F.O. Correia et alii, Frattura ed Integrità Strutturale, 31 (2015) 80-96; DOI: 10.3221/IGF-ESIS.31.07 94  K  [N.mm ‐3/2 ] da/dN  [mm/cycle] Experimental Data: R=0.0 P=0.01 P=0.05 P=0.50 P=0.95 P=0.99 1.0E‐6 1.0E‐3 1.0E‐2 200 1500 500 1.0E‐4 1.0E‐5 1000  K  [N.mm ‐3/2 ] da/dN  [mm/cycle] Experimental Data: R=0.25 P=0.01 P=0.05 P=0.50 P=0.95 P=0.99 1.0E‐6 1.0E‐3 1.0E‐2 200 1500 500 1.0E‐4 1.0E‐5 1000 a) b)  K  [N.mm ‐3/2 ] da/dN  [mm/cycle] Experimental Data: R=0.5 P=0.01 P=0.05 P=0.50 P=0.95 P=0.99 1.0E‐6 1.0E‐3 1.0E‐2 200 1500 500 1.0E‐4 1.0E‐5 1000 c) Figure 17: Probabilistic prediction of the fatigue crack propagation based the p-SWT-N field, for the S355 steel: a) R σ =0; b) R σ =0.25; c) R σ =0.5. C ONCLUSIONS n assessment of the UniGrow model was presented in this paper, based on available experimental data for the S355 mild steel. The UniGrow model was also extended to predict probabilistic fatigue crack propagation fields, replacing the deterministic SWT-N relation proposed in the UniGrow model by p-SWT-N or p-ε a -N fields. The p- SWT-N field was firstly proposed in the present paper, as a generalization of the p-ε a -N field, in order to take into account the mean stress effects. Elastoplastic finite element analysis was used to compute the residual stress field which is a more accurate than using the analytical elastoplastic formulae that does not account for stress redistribution due to yielding. The predicted p-da/dN-  K-R field for the S355 steel, based on the material p-SWT-N field, showed a satisfactory agreement with the available experimental data. The proposed p-da/dN-  K-R fields were able to model conveniently the stress R - ratio effects on crack propagation rates as well as to represent the scatter on these fatigue crack propagation rates. The elementary material block size found for the material is within the same order of magnitude for this parameter found by Noroozi et al. [10]. A CKNOWLEDGEMENTS he authors acknowledge the Portuguese Science Foundation (FCT) for the financial support through the doctoral grant SFRH/BD/66497/2009. A T