An Integral Probabilistic Approach for Fatigue Lifetime Prediction of Mechanical and Structural Components

iv in the proposed modelling is the replacement of the deterministic strain-life model by an existing probabilistic strain-life field based on Weibull distribution. The use of a fatigue damage parameter sensitive to mean stress allowed the formulation of the propagation model accounting for mean stress effects. The resulting probabilistic fatigue crack propagation model is demonstrated for two materials representative of old Portuguese metallic riveted bridges (Eiffel and Fão bridges), and for current steels, namely the S355 construction steel and the P355NL1 steel, covering distinct stress R−ratios. It is also proposed a unified local approach in order to model both crack initiation and crack propagation. In this thesis, two notched details, one made of P355NL1 steel and another made of puddle iron from the Eiffel bridge, are modelled in order to generate S-N curves for distinct stress R-ratios. The predictions are compared with available experimental data. The probabilistic S-N field is proposed for the notched details and a good correlation of the available experimental data is observed. This research finalizes with some probabilistic interpretations of fatigue damage accumulation under variable amplitude data, supported by the probabilistic Weibull field and its normalized variable V that is adopted as a damage measure. In particular, an approach is proposed to associate a cumulative distribution function to the classical Miner number without the need of performing extensive variable amplitude testing aiming. This approach is discussed and applied to smooth specimens made of P355NL1 steel and to a riveted joint made of a puddle iron original from the Fão bridge.