Stress- and strain-based approaches for fatigue life evaluation of complex structural details

The present work starts from the idea to improve fatigue strength of an actual structural detail where welded joints are subject to proportional biaxial variable-amplitude loadings leading to elastic-plastic strains. After a brief discussion on how to manage low-cycle fatigue in ship structural design, the case study is presented. Basing on outcomes drawn from the analyses performed on the considered structural detail, a critical examination is carried out on the procedures applied to check fatigue strength. A comparison of fatigue damages obtained from application of linear elastic approach and elastic-plastic approach is outlined in order to analyze advantages and drawbacks of the two approaches and their potential to be implemented in a design-oriented practical assessment procedure. Investigations point out that nonlinear approach may be a valid alternative to linear one only if designer can control safety factors relating to fatigue capability and has available deeper information on material behaviour and load history experienced by the structure.