Experimental and analytical investigation of fatigue characteristics of 350WT steel under constant and variable amplitude loadings

Fatigue analysis is a complex and uncertain process. Various models have been proposed; however, no universal or all-encompassing model exists.A state-of-the-art literature review of available fatigue crack propagation models, both for constant and variable amplitude loadings, was conducted to identify their advantages and limitations. Emphasis was placed on models that were simple to evaluate and required few (if any) empirical curve-fitting parameters.An experimental fatigue program was conducted, consisting of constant and semi-random (variable) amplitude cyclic loadings on 350WT steel 40J at −40°C. The fatigue models examined in the literature review were then compared to results obtained from the experiments.Findings for the constant amplitude loading (CAL) fatigue baseline data obtained experimentally for 350WT steel are reported and evaluated against the predictions by various models. Results of an experimental investigation into fatigue crack propagation (FCP) response of the steel under variable amplitude loading (VAL), consisting of CAL with random overloads (OL) is also presented. This includes a summary of theoretical models applicable to VAL fatigue crack propagation, and comparison of the experimental results to the models.