Modelling probabilistic fatigue crack propagation rates for a mild structural steel

Abstract

ABSTRACT.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 elasticplastic 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.

Statistical analysis of fatigue crack propagation data of materials from ancient portuguese metallic bridges

“…Others authors have performed similar work for other centenary bridges [8,9]. Correia et al [6,10,11] and Bogdanov et al [12] have proposed probabilistic curves for the fatigue crack growth propagation curves for several materials. Correia et al [6,10,11] proposed the probabilistic fields for fatigue crack growth using the probabilistic fatigue local approaches using old materials from riveted steel bridges and current steels.…”

Probabilistic fatigue S-N curves derivation for notched components

“…The crack propagation will be performed using the so-called UniGrow model, using probabilistic fatigue damage fields. The value of the elementary material block size, ρ*=12×10 -4 m, was estimated in the reference [9], using fatigue crack propagation data from CT specimens.…”

“…3. A value of the elementary material block size, ρ*=12×10 -4 m, was previously estimated using an independent identification based on pure fatigue crack propagation data (see reference [9] for details). Finite element models of the detail were used to perform elastoplastic stress analyses aiming the computation of the residual stresses.…”

“…The resulting data shows a good linear correlation. The p-S-N p field of the structural detail was calculated for R=0 using the p-SWT-N field of the material from the Eiffel bridge together with the UniGrow model proposed by Noroozi et al [2], and assuming ρ*=12×10 -4 m (see reference [9]). The use of the p-SWT-N field of the material from the Eiffel bridge to model the fatigue crack propagation is justified by the fact that the material showed a crack propagation rate sensitivity to stress ratio effects as argued in Reference [9].…”

“…The fatigue crack propagation is considered a damaging process consisting on continuous crack initializations over adjacent material representative elements of a size, ρ*. Based on pure fatigue crack growth data, the material representative element size, ρ*, was previously estimated as can be consulted in references [5][6][7][8][9]. Probabilistic fatigue crack initiation fields (p-S-Ni fields) are determined using an elastoplastic approach together with the material p-SWT-N fields.…”