Issue 31

J.A.F.O. Correia et alii, Frattura ed Integrità Strutturale, 31 (2015) 80-96; DOI: 10.3221/IGF-ESIS.31.07 80 Modelling probabilistic fatigue crack propagation rates for a mild structural steel J.A.F.O. Correia, A.M.P. de Jesus University of Trás-os-Montes e Alto Douro, Vila Real, Portugal UCVE-IDMEC-LAETA, Porto, Portugal jcorreia@utad.pt, ajesus@utad.pt A. Fernández-Canteli University of Oviedo afc@uniovi.es R.A.B. Calçada Faculty of Engineering, University of Porto, Porto, Portugal ruiabc@fe.up.pt A BSTRACT . A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force assessment, allowing mean stresses and loading sequential effects to be modelled. An extension of the fatigue crack propagation model originally proposed by Noroozi et al. (2005) to derive probabilistic fatigue crack propagation data is proposed, in particular concerning the derivation of probabilistic da / dN - ΔK - R fields. The elastic-plastic stresses at the vicinity of the crack tip, computed using simplified formulae, are compared with the stresses computed using an elastic- plastic finite element analyses for specimens considered in the experimental program proposed to derive the fatigue crack propagation data. Using probabilistic strain-life data available for the S355 structural mild steel, probabilistic crack propagation fields are generated, for several stress ratios, and compared with experimental fatigue crack propagation data. A satisfactory agreement between the predicted probabilistic fields and experimental data is observed. K EYWORDS . Fatigue, Crack propagation, Fracture mechanics, Local approach, Probabilistic approach, Finite Element Modelling. I NTRODUCTION atigue of materials and structures has been investigated for more than 150 years [2]. Although it still attracts a lot of attention of engineers and scientists. Concerning the investigation of the fatigue crack propagation, significant developments were carried out since the original Paris et al. [3] milestone contribution. Paris et al. [3] was pioneer suggesting the stress intensity factor range as a crack driving force parameter. The so-called Paris’s law stated this relation F